Water-Saving Agriculture and Sustainable Use of Water and Land Resources Edited by Shaozhong Kang, Ph. D., Professor Bill Davies, Ph. D., Professor Lun Shan, Ph. D., Professor Huanjie Cai, Ph. D., Professor
Shaanxi Science and Technology Press Xi
Foreword Shortage of water resources and deterioration in the quality and availability of agricultural land are worldwide problems. Water and land are critical resources and cannot be regarded as available in abundance. Degradation of land, reduction of river flow and the increasing frequency of severe dust storms have seriously damaged the natural environment and retarded economic development. These problems have reached dangerous levels in many countries. It is widely believed that an increase the efficiency with which water is used in agriculture is one key way to reduce many of these problems. For many countries, agriculture is the largest water user and to improve water use efficiency in agriculture would have a significant impact on sustainable development. It is not only important to ensure availability of water in the right quantity at the right time, but also important to ensure that water of an appropriate quality is used in agriculture. Therefore, research on water efficient agriculture, and on sustainable use of water and land resources in arid and semiarid areas has a high international priority. Water shortage in China, particularly in Northwest China is very serious. This region (including Shaanxi, Gansu, Ningxia, Qinghai, Xingjiang and Western Inner Mongolia) accounts for 1/3 of the area of China, but has only 8.3% of total national available water resources. While the water shortage in this region is serious, the waste of water resources and water pollution remain as major issues. Overall irrigation water use efficiency is approximately 40%, with atypical irrigation water productivity around 0.46 kg/m3. Excessive irrigation in Ningxia and Inner Mongolia have had a significant influence on Yellow River downstream water users. The frequency and severity of dust storms, sourced from the Northwestern China, have been increased every year. This is accompanied by an increase in the desertification of large areas of land. The importance of water-saving agriculture and sustainable use of water and land resources are increasingly being recognized by public and government authorities. To address many of the important issues raised above, the
plant improvement for water-saving in water-limited areas and dryland, irrigation technology and water management, sustainable use of water resources in arid and semiarid areas, agricultural water and land environment. The secretariat received more than 240 abstracts, all of them were edited, they and with the selected some full papers will be published in the special issue of Journal of Experimental Botany, and the other full papers, which the secretariat received, are published in this proceedings. We thank Du Taisheng, Martin Parkes, Jeff Gale, Rupert Knowles, Rachel Caiger,Wang Zhinong, Hu Xiaotao, Ma Xiaoyi and the anonymous reviewers who helped in checking papers and in preparing the conference.
Shaozhong Kang, Bill Davies, Lun Shan and Huanjie Cai August 16, 2003
CONTENTS Section I Biological Mechanisms of Water-saving Agriculture Biological water-saving approaches and future perspectives…………………………1001 Lun Shan, Xiping Deng, Suiqi Zhang and Shaozhong Kang Yield response to pre-planned water-deficit irrigation…………………………………1002 Cevat Kirda Remotely-sensed canopy temperatures used for irrigation timing linked to crop water stress index (CWSI)…………………………………………………………………………1003 Angela Anda Improving water use efficiency based on comparative sensitivity of soybean stomatal conductance and photosynthesis to soil drying…………………………………………1004 Fulai Liu, Mathias N. Andersen, Christian R. Jensen High wheat water use efficiency of limited water in semi-arid areas………………… 1005 Xiping Deng, Lun Shan, Shaozhong Kang, Inanaga Shinobu and M. Elfatih K.Ali Puddling depth and intensity effects in rice-wheat system on water use and crop performance in a sandy loam soil……………………………………………………… 1006 S.S. Kukal Water use efficiency of Oilseed Rape (Brassica Campestris) under even or patchy water supply…………………………………………………………………………………… 1007 Ling Wang, Hans de Kroon, Toine Smits Evaluating water-use efficiency of rainfed wheat using a simulation model…………1008 Senthold Asseng and Neil C. Turner The Andean grain crop quinoa (Chenopodium quinoa Willd.) aintains photosynthesis and increases water use efficiency during soil drying…………………………………1009 Sven-Erik Jacobsen, Fulai Liu, Christian Richardt Jensen Towards the improvement of drought resistance in lupin ……………………………………………………………………………………… 1010 Jairo A. Palta, Neil C. Turner, Robert J. French and Bevan J. Buirchell ……… 1011 Tiantian Hu, Shaozhong Kang, Mingxia Gao and Fucang Zhang ……………… 1012 Haibin Shi, Takeo Akae, Dong Kong, Lihui Zhang, Yaxin Chen, Zhanmin Wei, Yanlin Li and Yiqiang Zhang …………………………………………………………………………………… 1013 Wenjuan Shi, Shaozhong Kang and Xiaoyu Song
Crop yield and water use of spring wheat in arid area of China…………………… 1014 Zhanmin Wei, J.C. Van Dam, R.A. Feddes, Yaxin Chen1, Haibin Shi and Zhongyi Qu Effect of nitrogen and phosphorus-nutrition on maize root hydraulic conductivity under water deficiency………………………………………………………………………… 1015 Suiqi Zhang, Zixin Mu, Xiaoqing Yang, Zongsuo Liang and Lun Shan
Ⅰ
Biological water-saving approaches and future perspectives Lun Shan1, Xiping Deng 1, 2, Suiqi Zhang 1 and Shaozhong Kang 2 1
Institute of Soil and Water Conservation, Chinese Academy of Sciences, Shaanxi, 712100, China. Northwest Sci-Tech University of Agriculture and Forestry, Shaanxi, 712100,China.
2
Abstract Increasing the efficiency of water use by crops continues to escalate as a topic of concern because drought is an important environmental factor limiting crop productivity worldwide. Greater yield per unit rainfall is one of the most important challenges in water-limited agriculture. Besides water-saving irrigation and conservation tillage, a good understanding of factors limiting and/or regulating yield now provides us with an opportunity to identify and then select for physiological and genetic breeding traits that increase the efficiency of water use and drought tolerance under water limited conditions. Biological water-saving may be one means of achieving this goal. We propose the term biological water-saving to describe an increase in crop water use efficiency (WUE) and drought tolerance through genetic improvement and physiological regulation. The preponderance of biological water-saving measures in agriculture is discussed giving principles and potential of the technology.
Key words: Biological water-saving, water use efficiency, drought tolerance, physiological regulation, water-saving breeding.
E-mail:
[email protected].
1 Preponderance of biological water saving measures in agriculture About 40% of the land in the world is under arid and semiarid climatic conditions (Stewart, 1988; UNEP, 1997; Gamo, 1999). In China, water limited farm land occupied above 70% of total arable land, located mainly in Northern part of China,
in
particular
Loess
Plateau
and
surrounding area, which accounts for about 70%
1
drought tolerance and water efficient potentials
for sustainable water use, water saving concepts
from physiological and genetic approach are not
in irrigated agriculture has been proposed (Shan
yet achieved.
and Xu 1991, Deng et al. 1995, Shan 1998, Deng et al 2003).
Biological water-saving approach in our discussion includes some physiological adaptation and genetic traits that alters crop drought tolerance or/and water use efficiency (WUE). Physiological adaptability and genetic traits can affect water status within the plant, and the impact of these changes on plant response in terms of improved
plant
growth
or
yield
offers
opportunities to increase WUE by plant it self. This report will focus on biological water-saving principle and approaches to provide a strong foundation for
understanding the role of
physiological and genetic improvement on WUE. Water plays a vital role in meeting the demand for food of the growing population, indeed, irrigated agriculture is considered as the major user of water in the world. In some studies, they claim that the general trend to the use of water is increasing significantly.
This led to some
conclusions that water scarcity problem could be inevitable in the near future. In response to the call Water Efficient Agriculture System
Spatial and Temporal Adjust Water Resources
Effective Use Natural Rainfall
Rational Use Irrigation Water
Increase Plant Water Use Efficiency
2
Increase adaptability to water deficient
Raise the ratio of photosynthesis/transpiration
Select high WUE varieties
Adjust cropping system
Optimize irrigation system and reduce irrigation quorum
Improve irrigation method and reduce irrigation quorum
Reduce the loss of water transportation
Hold and store runoff for supplemental irrigation
Expand root system to use soil storage water efficiently
Rationalize tillage add mulch and reduce surface evaporation
Control soil and water loss promote rainwater permeation
Combine well and channel irrigation with effective use of surface and ground water
Construct reservoir to adjust water use yearly and seasonally
Transport water by project to adjust regionally
Figure 1. Components of water efficient agricultural system and its regulating elements
Water efficient agriculture refers to integrated farming practices which are able to sufficiently use of natural rainfall and irrigation facilities for improving water efficiency (Shan 2002). The core objectives in research and development of water efficient agriculture is to raise the water use rate
2 Fundamentals of biological water-saving
and efficiency and promote crop yield increase,
2.1 Effect of water deficit on several physio-
i.e. on irrigated land, to achieve a high crop yield
logical processes
and to save a massive quantity of water simultaneously, or on non-irrigated land, to control crop water requirement as much as possible with little influence on bumper harvest (Deng et al. 2002a). The scientific measures in water efficient agricultural system here we proposed includes spatial and temporal adjust water resources, effective use natural rainfall, rational use ～
irrigation water and increase plant WUE (Fig. 1). ～
In the agricultural practices, several considerations should be also take into account, which including the water-saving performance of farming areas, quantity, quality, spatial and temporal distribution of water resources. it is also important to establish cultivation norms in order to
reduce water
consumption and to reshape the existing farming structure and cropping system in line with the current distribution pattern of water resources. In another
aspect,
sufficient
manpower
and
equipment need to be mustered for the research, development, production, supply and maintenance of water-saving materials, spare parts, devices, instruments and facilitates. In the social security aspect, relevant laws and statutes concerning water management need to be enacted, formulated
3
～
～
simultaneously induced the midday depression in
1996). Reduced cell expansion carries a primary effect
photosynthesis, indicating that both stomatal and
on meristematic development of yield components,
non-stomatal limitations were responsible for
such as the inflorescence or the tiller initial in the
photosynthetic decline in spring wheat under the
cereals - leading to potentially small reproductive
semiarid environment.
organs and reduced yield. This is an irreversible
Shortage of assimilates and sometimes nitrogen
structural effect that is difficult to be amended by
availability is a major cause of arrested grain and
re-watering. It can however be amended to some
fruit growth during drought stress. Drought stress
extent by inter-organ compensation following
during cereal grain development reduces the
watering, such as tillering in the cereals. The
duration of grain filling. If the rate of grain filling
meristematic tissues are generally positioned
is not adjusted upward, final grain weight is
within the plant in a relatively protected
reduced. Increased grain growth rate under
environment as compared with that of a fully
drought stress depends on the supply of
expanded leaf and therefore it may take a sever
assimilates. This supply is becoming short due to
stress for meristem to loose its turgor.
the inhibition of current photosynthesis during
Under the water deficit conditions photosynthesis
stress. An alternative source of assimilates are
was variable under different drought patterns and
pre-anthesis stem reserves in the form of sugars,
drought speed (Deng et al. 1996). Under gradual
starch or fructans, depending on the species.
soil drying conditions, crop exhibited higher
These reserves are readily utilized for grain filling
photosynthetic rate than under fast soil drying
and their availability may become a critical factor
conditions. In the former, osmotic adjustment
in sustaining grain filling and grain yield under
increased to a certain extent while under the latter
drought stress.
process it remained constant. Osmotic adjustment
According to the available data, It is suggested
allows for maintenance of photosynthesis and
that the order in which crop physiological
growth by stomatal adjustment and photosynthetic
processes are serially affected by drought seems
adjustment (Turner 1986; Shangguan et al. 1999).
to be growth, stomatal movement, transpiration, photosynthesis and translocation (Shan and Chen
The reported evidence showed that under mild
1998; Deng et al. 1999; Deng et al. 2000b).
and/or moderate soil water deficit conditions, photosynthetic depression was caused by stomatal closure or stomatal limitation, but not by
2.2 Sensitivity to drought in different growth
biochemical reactions. However, under severe
stages
soil water deficit conditions, non-stomatal factors
Many studies (Mary et al. 2001; James et al.
including some limiting enzymes could have been
2001) have looked at the yield losses associated
responsible for the decline in photosynthetic
with drought at different stages of plant
capacity (Kalt-Torres et al. 1987; Du et al. 1996;
development. Villarreal et al. (1999) showed that
Du
in
crown root initiation and anthesis are the two
photosynthesis were mainly induced by severe
stages at which yield losses from drought stress
vapor pressure deficit, and stomatal limitation
can be most critical to wheat.
et
al.
1998).
Midday
declines
was suggested as a major cause (Schulze 1986;
Deng et al. (1995) showed that, in the Guyan
Xu and Shen 1997).
County of the Ningxia Uh Autonomous Region in
Under natural semiarid conditions, however,
China, where the annual precipitation was 450mm
this decline usually resulted from soil water
and the annual mean temperature was 6.5℃, a
deficit that induced a decrease in leaf water
single irrigation of 600 m3/ha applied at the
potential at midday. Deng et al. (2000a) reported
jointing, booting and grain filling stages,
that both soil water deficit and high VPD
respectively (equivalent to 30% of irrigated 4
＞
volume of water for a full cropping season with ＞
the highest yield) yields up to 75% of the highest yield were recorded only at the jointing stage. →
This amounted to a 2.8 kg increase in grain yield per cubic meter of water. Comparing with other stages, the optimum time for limited irritation in spring wheat was the jointing stage. The water deficit critical period and the optimum irrigation time in wheat, however, are not at the same growth stage. It seems essential to make a distinction between the critical growth stage at which yield is greatly reduced by drought from that one at which supplemental irrigation results in
2.3 Different varieties response to water deficit
2.4 Compensatory effects of crops adapted to drought
5
irrigation, crop water consumption, water use
compensatory
effect
that
could
reduce
efficiency and irrigation efficiency were much
transpiration and keep wheat growing and WUE
improved synchronously.
Limited irrigation
significantly increasing under drought conditions.
induced an obvious compensatory effect on wheat
According to our recent year research results, crop
WUE. Liang et al (2002) demonstrated that the
compensatory effect contributed to the biological
drying-rewatering alternation had a significant
water-saving is summarized in Figure 2.
Improve physiological functions including osmotic adjustment ability, stomatal regulation, ratio of photosynthesis to transpiration and reserve plant water status, plasma membrane stability, and antioxidation enzyme activities. Enhance leaf growth, leaf area, ratio of root/shoot, chlorophyll content, photosynthetic efficiency and dry matter accumulation.
Promote soluble carbohydrate retranslocation
Increase root system growth and extensity
Boost grain weight and harvest index
Enhance use of soil storage water
Increase yield and water use efficiency
Figure 2. Compensatory effects of crop plants adapted to moderate water deficit The nutrients that are found to be most limiting
of raise inorganic nutrition on the high efficient
in the loess hilly region of China are N and P
use of limited water in dry land wheat production.
(Shan and Chen 1993). The deficiency is really a problem of runoff (Wei et al. 2000). The yield and
3 Biological water-saving approaches
WUE increase from added N were observed in
3.1 Conventional breeding
several dryland areas where crops were grown on
The
biological
water-saving,
here
we
the same land for several years (Shan and Chen
proposed is that to increase crop WUE and
1993). Liu et al. (1998) indicated that maximum
drought tolerance by genetic improvement and
yield and highest WUE were achieved under the
physiological regulation, that is, to achieve high
optimum fertilizer input of 90 kg N and 135kg
efficient use of water by crop itself. Accordingly,
P2O5 per ha in the semiarid field conditions of
there is a need for accurately understanding that
loess hilly area in Ningxia. Increase Soil fertility
plant response to water deficit conditions on
was positively correlated with grain yield and
real-time. Therefore, better adaptation of crops
WUE of spring wheat, with a correlation
to limited water, are key issues for future
coefficient were 0.959 and 0.894. Increasing
research.
fertilizer level significantly increased fertile
At the whole-plant level, higher productivity
spikelets number, kernels per spike and kernel
will depend mainly on germ plasm improvements,
weight. Fertile spikelets number was sensitive to
such as stronger seedling establishment, increased
fertilization. Fertilization applied in spring wheat
rooting depth, increases in the harvest index (the
improved root system extension and especially
marketable part of the plant as part of its total
enhanced roots growth in the cultivated soil layer
biomass) and enhanced photosynthetic efficiency.
of 0-20 cm. Ameliorated root system was able to
Traditional breeding has already made progress in
improve crop water use and nutrient absorption
extending these achievements to other crops, and
and hence, crop yield and WUE was increased.
genetic engineering is expected to overcome
Their study highlighted the compensatory effects
long-standing obstacles to development of water
6
biomass growth (i.e., the water-use efficiency as
saving and drought-tolerant crop varieties. The agriculturally important crop species have
above-ground biomass/water use), and (iii) the
traditionally involved the use of selective
harvest index. Since these three components are
breeding to bring about an exchange of genetic
likely to be largely independent each other, then
material between two parent plants to produce
an improvement in any one of them should result
offspring having desired traits such as drought
in an increase in yield. Improvement of
tolerance and enhanced WUE. The exchange of
water-use efficiency of new wheat varieties of
genetic material through conventional breeding
particular
requires that the two plants being crossed are of
transpiration efficiency of the crop, (2) reducing
the same, or closely related species. Such active
wasteful tillers, and (3) longer coleoptiles so
plant breeding has led to the development of
crops can be sown at optimal sowing time even
superior plant varieties far more rapidly than
when moisture is deep. Deep root systems are
would have occurred in the wild due to random
able to uptake water from the soil and improve
mating. However, traditional methods of gene
crop water use under water-limited conditions.
exchange are limited to crosses between the
The simplest way to increase rooting depth and
same or very closely related species; it can take
root distribution of crops is to increase the
considerable time to achieve desired results and
duration of the vegetative period. This may be
frequently, characteristics of interest do not exist
achieved by sowing earlier or later flowering
in any related species. For example if one is
genotypes.
importance
are:
(1)
improving
interested in introducing drought tolerance in wheat, then it has to be crossed with a closely
3.2 Physiological approach
related species having strong drought tolerance.
Plants are grouped into three main biological
In many of such cases desirable germplasm is
classifications as far as carbon dioxide fixation is
not available.
concerned - C3, C4, and CAM. These are the
Genetic improvement for water-use efficiency
different types of bonding sites (receptor sites)
has been a major research thrust in most of the
for carbon dioxide. Thus both the CAM and C4
arable crops. The importance of genetic
pathways are mechanisms to increase WUE.
enhancement
Because C4 plants exhibit greater efficiency than
for
improved
adaptation
to
water-limited conditions and efficient water use
C3 species with respect to water, light, and
has been long recognized by International Crops
nitrogen use. Once the bonding process is
Research Institute for the Semi-Arid Tropics
complete a series of chemical reactions occur to
(ICRISAT) (Nigam et al. 2001). The groundnut
break down the carbon dioxide and water to
breeding grogram has adopted three major
create carbohydrates. An enriched carbon
strategic approaches to enhance adaptation of
dioxide atmosphere can give an increase in
groundnut to drought prone environments. (1)
photosynthesis of between 30 and 60%. In CAM
Development of short-duration genotypes that
pathway, initial nocturnal CO2 fixation by PEPC
can escape the end-of-season drought; (2)
occurs
Development of genotypes with superior yield
transpirational water losses are low. CO2 release
performance in drought prone regions following
during the day promotes stomatal closure and
conventional breeding approach; (3) Development of
concentrates CO2 around Rubisco, suppressing
drought resistant genotypes following physiological
its oxygenase activity, thereby minimizing
breeding approach. Passioura (1977) proposed
photorespiration.
that when water is limiting then grain yield is a
CO2-concentrating strategy is that CAM plants
function (i) the amount of water used by the crop,
exhibit WUE rates several fold higher than C3
(ii) how efficiently the crop uses this water for
and C4 plants under comparable conditions 7
when
stomata
The
net
are
open
effect
of
and
this
(Drennan and Nobel, 2000). Most notable
material relative to the value the same ratio in the
among these are commercially or horticulturally
air on which plants feed. Condon et al. (2002)
important plants such as pineapple (Ananas
showed that△13C is positively related to the ratio
comosus), agave (Agave subsp.), cacti (Cactaceae), and
of the intercellular CO2 concentration and the
orchids (Orchidaceae).
atmospheric CO2 concentration. Therefore △13C
Physiological approaches are used to (i)
correlates with WUE. Consequently, △13C, due to
identify indirect selection criteria for early
its convenience and relatively cheap cost, has
generation selection, (ii) exploit new sources of
become a useful indicator of differences in WUE.
genetic diversity from germplasm collections,
Recently this method has been used for high
(iii) understand physiological bases of improved
WUE breeding in wheat. Other techniques such as
drought tolerance and WUE in elite materials.
genome-wide tools and thermal or fluorescence
Under water deficit conditions, the crop is able to
imaging may allow the genotype
synthesize abscisic acid (ABA) by its root system. ABA is then transported through the xylem to leaves, causing regulation of several
3.3Plant genomes scan and molecular markers
ion channels in guard cells that trigger stomatal closure (Grill and Ziegler 1998; Pei et al. 1998). The plant hormone ABA plays a central role in the long distance drought signalling process to mitigate drought damage by regulating leaf transpiration in many plants. ABA is an effective stomatal regulating hormone, the relationships between stomatal conductance and xylem (ABA) generated from data collected in the field suggest that ABA can have a controlling influence and determine day to day variation in stomatal behavior as soil dries, as well as leaf to leaf variation in stomatal conductance when different cultural treatments are applied (Davies et al 2002). Dry et al. (1996) and Kang et al. (2000) demonstrated partial root zone drying is an irrigation technique that has been developed to allow exploitation of the plant’s long distance signalling system. When the system is optimized, stomatal behavior, shoot water status and leaf growth can be regulated so that WUE can be significantly increased. Due to crop responses to drought stress are complex, the functions of many other genes are still unknown. The new tools that operate at molecular, whole-plant and ecosystem levels are revolutionizing our understanding of plant response to drought, and our ability to monitor it. For example, Carbon isotope discrimination (△ 13
C) is a measure of the
13
C/12C ratio in plant 8
molecular basis of stress tolerance (Cattivelli et al. 2002). Responses to drought in barley were monitored by microarray hybridization of 1463
2
DNA elements derived from cDNA libraries of 6 and 10 h drought-stressed plants. Functional identities indicated that many cDNAs in these libraries were associated with drought stress. Hybridization experiments were analyzed for drought -regulated sequences, with significant changes defined as a deviation from the control exceeding 2.5-fold. Responses of transcripts showed stress-dependent expression patterns and time courses. Nearly 15% of all transcripts were either up- or down-regulated under drought stress.
Transcripts
that
showed
significant
up-regulation under drought stress are exemplified by
asmonate-responsive,
metallothionein-like
late-embryogenesis
3. 4 Transgenic approach
Lycopersicon esculentum L. pennellii
3
Moricandia
Themophila
3
4
4
Brassica
Brassica Moricandia
nitens 9
Brassica oleracea
napus
genetic map of M. nitens, based on RPLP loci, is being developed and used for comparative mapping of Brassica and Moricandia. This comparative mapping will allow the marker assisted interspecies transfer of the genes controlling C3C4intermediate metabolism. Garg
et
al.
(2002)
demonstrated
that
depending on growth conditions, the transgenic rice plants accumulate trehalose at levels 3
2
4
3
2
4
4 Future Perspectives
HVA1
LEA
HVA1
10
3
in plants to switch on an array of genes in
paradigm shift in research approach to a complex
response to dehydration. Some of these genes
trait such as drought tolerance.
code for proteins that help protect various parts of
Green Revolution wheat, rice and maize
the plant cell during water loss while others
varieties that are insensitive to day-length and of
detoxify harmful substances. (Singh et al 2002,
short to medium duration (90-120 days) have
Xiong et al. 2002) Understanding how it would be
proved successful in escaping late-season drought
best to utilize these genes is a lengthy process.
that adversely affects flowering and grain
CIMMYT researchers have initially focused on
development. As a result, modern rice varieties
incorporating a type of DREB gene (encoding a
are three times more productive, in terms of water
’dehydration-responsive element binding’ protein),
use,
which enables the wheat plants to withstand
breeding has already made progress in extending
extreme water loss. Unfortunately, when this gene
these achievements to other crops, and genetic
is continually "switched on", plants are smaller
engineering is expected to overcome long-
and produce much lower yields than unmodified
standing obstacles to development of higher-
varieties significant disadvantages when it comes
yielding, drought-tolerant crop varieties.
than
From
to plant breeding. But the scientists then found
traditional
the
varieties.
standpoint
of
Traditional
agricultural
that by fusing the DREB gene with the promoter
biotechnology, advances in genomics will lead to
region of another gene (rd29A), it is switched on
a rapid increase in the number of useful traits that
only under stress conditions of dehydration or
will be available to enhance crop drought
cold temperatures. The result is a plant that has a
tolerance and WUE in the future. Thus the plant
normal growth pattern and yield in good
breeders will have an unlimited access to the
conditions, but is also much more resistant to
gene pool of the entire living kingdom for
drought, freezing, and high salinity. More work is
incorporation of desired traits into the crop
now needed to fully characterize the function of
species. A better understanding of the integration
the additional gene, and to dissect the complex
of these plant traits and their genetic control will
process by which this gene is expressed.
provide opportunities for improving drought
Recent molecular biology research in drought
tolerance and WUE in modern crop plants, such
tolerance in plants has focused at the cellular and
as rice and tomato, and increased agricultural
biochemical levels on response to extreme or
production in the face of limiting water supplies
short-term shock treatments, seeking to identify
throughout the world. Considerable potential for
signaling or regulatory genes involved. However,
further improvement in crop productivity in
drought tolerance in economic terms requires
semiarid environments seems to depend on
crops that use water efficiently (for the
sufficient conservation of moisture and efficient
environments that they are in), have higher net
use of this limited water. Different crop, soil and
carbon gain and partition carbon to maximize
water management strategies should be adjusted
grain yield. Use a functional genomics approach
according to the conditions that prevail in the
that involves microarrays and physiological
various water limited areas. By combining soil
analysis at plant and crop levels. It will identify
and water conservation practices with adjusting
and functionally assay profiles of coordinately
the
expressed genes involved in plant developmental
drought-tolerant and water efficient varieties,
response to drought patterns experienced by crops
increases in crop productivity could be achieved.
in production environments. High throughput genomics and marker technologies, together with bioinformatics analyses of data generated in the lab and field, provide an opportunity for a 11
cropping
system
by
cultivating
Acknowledgements This paper was supported by The Major State Basic Research Development Program of
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15
Yield response to pre-planned water-deficit irrigation Cevat Kirda Cukurova University, Faculty of Agriculture, 01330 Adana, Turkey
Abstract Yield responses to pre-planned-deficit irrigation are reviewed for cotton, maize, potato, soybean, wheat, common bean, groundnut, sunflower and sugar cane. Crops including cotton, potato, maize, wheat, groundnut, common bean, sunflower, soybean, sugar beat and sugar cane are well suited to deficit irrigation practices if reduced evapotranspiration is imposed only during a certain growth stage or stages. Among these crops, cotton, groundnut and maize can withstand reduced evapotranspiration imposed throughout the whole growing season without significant yield reduction. Mechanisms contributing to crop tolerance to temporal water stress, developed during deficit irrigation, differ depending on crop species. Maize develops an adaptive strategy of extending rooting depth and extracting water from deeper soil while simultaneously reducing leaf area to decrease transpiration. Soybean reduces shoot and root growth, decreases leaf chlorophyll and shoot soluble sugars, but increases soluble sugar content of roots for lowering osmotic potential. Adaptation of cotton to deficit irrigation practice may be attributed to uninterrupted biosynthesis of fatty acids that strengthen cell membranes. The osmotic adjustment ability of wheat cultivars, largely controlled by leaf sugar and proline concentrations, is another complex mechanism of field crops, which makes deficit irrigation a feasible option to increase water-use efficiency.
Keywords: Deficit irrigation, drought stress, drought tolerance, evapotranspiration, irrigation scheduling, osmotic adjustment, water stress. E-mail:
[email protected]
1 Introduction Oceans and seas contain 97.3% (1.36x109 km3) of the global mass of water, while the remaining 2.7% of water (37.8x106 km3) is found on continents with only a minute amount of 0.001% (13x103 km3) in the atmosphere (Todd, 1970). About 77.2% of the fresh water associated with land (37.8x106 km3) is frozen and tied up in ice caps and glaciers, and about 22% is found in ground water, much of which is economically irretrievable (Tanji, 1990). This leaves only a small percentage (?1%) as an easily manageable fresh water resource to meet the increasing needs of industry, households and agriculture. Water allocation for municipal and industrial use has to be increased to meet the needs of ever increasing world population, so the share of water allocated for agricultural use has to be reduced from the present 62.7% (Kirda and Kanber, 1999) to lower values in future decades. Developing countries have added 22.2 Mha of new irrigated areas in the last 15 years to feed their increasing population, which has added an additional strain to the already limited supply of world water resources. The highest additional demand of 438 km3 has occurred in the most populated continent, Asia (Finkel, 1982). The continents experiencing
the strongest water scarcity are Asia and Africa. Over 300 million people in 26 countries are presently suffering from water shortage, and it is expected that this number will increase to over 400 million in the year 2010. Nine out of fourteen countries are already on the verge of alarming water shortages in the Middle East (Hamdy, 1995). Water pollution, excess irrigation and poor management of irrigation schemes have worsened the problem further and created water shortage even in countries with high rainfall. World population will stabilise around 10.5 billion, of which 87% will be living in the developing countries by the year 2100 (Sadik 1988). Among the challenges for sustaining adequate supply of food and fibre is to develop new innovations to increase effective use of continuously decreasing water supply for irrigated agriculture. In addition other measures are required like prevention of soil degradation in tropical and sub-tropical soil systems, developing environmentally friendly practices of fertiliser and pesticide use and searching for high yielding plant genotypes. Irrigated agriculture is practiced on 18% (220
provides more than one third (36%) of the
2.3 Soybean et al
2 Rationale of deficit irrigation practice 2.1 General
et al.
et al et al et al
2.2
Maize
2.4 Cotton
ability to maintain low leaf-water potential and to osmotically regulate leaf-turgor pressure, socalled conditioning. Thomas et al. (1976) found that plants suffering a gentle water stress during the vegetative period showed higher tolerance to water deficit imposed at a later growing stages as a result of adaptation to existing soil water status. In concert with this finding, Hearn and Constable (1984) recommended that the optimum practice was not to irrigate cotton until 60 days from sowing and until plant available water in the root zone reaches 50%. Grimes and Dickens (1977) reported that both early and late irrigations lowered cotton yields. However, water stress during vegetative growth, causing leaf water potentials less than a critical mid-day value of 1.6 MPa, adversely affected final yield (Grimes and Yamada, 1982). Pham Thi et al. (1985) showed that water stress provokes inhibition of fatty acid desaturation, resulting in a sharp decrease of linoleic and linolic acid biosynthesis in drought-sensitive cotton varieties; however, lipid and fatty acid metabolism of droughtresistant varieties shows less variation and greater stability. So it may be very likely that adaptation of cotton to temporal drought conditions of deficit irrigation practice may be attributed to uninterrupted biosynthesis of fatty acids, which strengthen cell membranes. The cotton capsule and fruits generally have higher water and osmotic potential. Their water status are less sensitive to drought than that of the subtending leaf and bracts; this attests to the phloem playing an important role in water transport to developing cotton fruits (Van Iersel and Oosterhuis, 1996). Hence yield benefit of irrigation at yield formation stage of cotton may only be marginal. An economic analysis carried out by English and Raja (1997) showed that irrigation deficits of between 15 to 59% for cotton would be economically acceptable. A wide range of variation in acceptable deficit irrigation depends on local circumstances such as cost of irrigation water, cotton price, irrigation method and the like. 2.5 Wheat Work by Day and Intalap (1970), Musick and Dusck (1980), Singh et al. (1984) and many others showed that deficit irrigation could also be acceptable practice for wheat irrigation without appreciable yield reduction. Zhang et al. (1998) demonstrated that wheat grain yield reduction would be limited to only 15% if a single irrigation, instead of the common practice of four irrigations, is used for wheat in north China. A single irrigation with 75% decrease in irrigation water requirement will ensure sustainable wheat cropping without depleting scarce underground water resource in the area. Mugabe and
Nyakatawa (2000) found that yield response of wheat to deficit irrigation showed genotypic variability. Bajji and Kinet (2001) showed that differences in osmotic adjustment ability of wheat cultivars, largely controlled by leaf sugar and proline concentrations, might be responsible mechanisms for genotypic variability. 2.6 Potato The effect of deficit irrigation at different growth stages on potato yield has also been studied ( Bartoszuk, 1987; Trebejo and Midmore, 1990; Minhas and Bansal, 1991; Shock et al., 1992). The results suggest that deficit irrigation of potatoes may be difficult to manage compared with crops showing some level of resistance to drought or avoiding water stress by deep rooting (Shock and Feibert, 2002). It should be noted that even a brief period of water stress following tuber set may cause reduction in tuber yield and quality (Shock et al., 1993; Elredge et al., 1992; Lynch et al., 1995). However, results of a field experiment reported by Fabeiro et al. (2001) showed that potato yield obtained under deficit irrigation imposed at early stage of growth (vegetative and tuber bulking) was nearly same as that of the control treatment receiving full irrigation. However, results of Iqbal et al. (1999) suggest that water deficit at early development stages causes greatest tuber yield reduction compared with stress developed later, during the ripening stage. Differences in yield response of potato to deficit irrigation may be attributed to varietal differences in tolerance to water stress (Miller and Martin, 1987; Lynch and Tai, 1989; Jefferies and MacKerron, 1993). So deficit irrigation practice should be re-examined with field tests for newly introduced potato cultivars before recommendations are made for the irrigation requirements. 2.7 Summary Similar work on cowpea (Ziska and Hall, 1983), sugar beet (Okman, 1973; Oylukan, 1973; Winter, 1980), sugarcane (Pene, 1994; Pene and Edi, 1999), sunflower (Jana et al., 1982; Rawson and Turner, 1983; Connor et al., 1985; Karaata, 1991), groundnut (Stirling et al., 1989; Ahmad, 1999) and on many other crops, have demonstrated that optimum crop yields may be obtained under deficit irrigation practices. A certain level of yield loss should be allowed for a given crop with higher returns gained from the diversion of irrigation water to other crops. If water scarcity exists at regional level, irrigation managers should adopt the same approach to sustain regional crop production, and thereby maximise income (Stegman et al., 1980). This new concept of irrigation scheduling is given different names, such as regulated deficit
irrigation, pre-planned deficit evapotranspiration and deficit irrigation (English et al., 1990).
on plant species, variety, irrigation method and management and growth stage when deficit irrigation is imposed (Kirda, 2002). The crop response factor gives an indication of whether the crop is tolerant of water stress. A response factor greater than unity indicates that the expected yield reduction for a given evapotranspiration deficit is greater than relative reduction in evapotranspiration. Otherwise, response factors that are less than unity represent situations where deficit irrigation practice should be a feasible option and promoted if water availability is a major constraint. As it can be seen in Figure 1, soybean and maize respond differently to deficit irrigation, depending on the time when the deficit irrigation or water stress is imposed. Waterdeficit scheduling for soybean must be during the early growth period from vegetation till early flowering; whereas, for maize it should be delayed until late tasselling and early yield formation stages to ensure that final yields are influenced least. 3333333333333333333333333
3 Deficit Irrigation scheduling 3.1 Response factors Deficit irrigation can either be practiced throughout the whole growing season. Alternatively it may be confined to a given growth period, depending on the crop species itself, to water allocation programs in an irrigation schemes or to a particular irrigation practice preferred by the individual farmer. Cropyield response to deficit irrigation can be described by a simple linear equation of the form (Stewart et al., 1977)
?
1 ? Y ?Ym? 1 ? k y 1 ? ET ?ETm? 1
?
which is used to estimate relative yield reduction. In the equation, Y and Ym are expected and maximum crop yields, corresponding to actual (ET) and maximum crop evapotranspiration (ETm), respectively. The coefficient ky is called a crop yield response factor that varies depending 1-E T.E Tm 0.5
0.4
0.3
-1
0.2
0.1
0.0 0.0
S OYBEAN
Stre ss a t Yie ld form a tion ky = 1.25
1-Y.Ym
0.2
-1
0.1
S tre ss a t V e g. & Flow e ring ky = 0.77
0.3 0.4 0.5 0
0.3 M AIZE
Stre ss a t Ve ge ta tion ky = 1.32
1-Y.Ym
0.2
-1
0.1
S tre ss a t Flow e ring & Yie ld form a tion ky = 0.82
0.4 0.5
Figure 1 Comparisons of relationships between relative yield decrease and relative evapotranspiration deficits for soybean and maize (Data is from Kirda et al., 1995)
If growers have prior knowledge of the cropyield response to deficit irrigation, significant savings in irrigation water requirements can be achieved with only marginal yield reduction. Tables 1 and 2 list crop response factors for
water deficits imposed during the whole season and during specific growth stages, respectively. Deficit irrigation will then be an acceptable practice for saving irrigation water. It should be noted that yield response factors are lower for
deficits confined to specific growth stages, compared with the deficits imposed during the whole season. In the latter case, success of deficit
irrigation depends largely on inherent ability of crops to tolerate drought. 2222222222222222222
Table 1. Crop response factors for major field crops, when yield reduction is proportionally less than relative evapotranspiration deficit, imposed throughout the whole season (Kirda, 2002) Crop
ky
Irrigation method
Common bean
0.99
Sprinkler
Cotton
0.86
Drip
Maize
0.74
Sprinkler
Sunflower
0.91
Furrow
Karaata (1991)
Sugar beet Potato
0.86 0.83
Furrow Drip
Bazza and Tayaa (1999) Kovacs et al. (1999)
Wheat
0.76 0.93
Sprinkler Basin
3.2 Irrigation timing Amount of irrigation water alone does not determine final crop yield. Timing of irrigation is even more important than over-all irrigation water applied to get the highest yield benefit from irrigation. Figure 2 demonstrates how strongly the final yield of soybean depends on the timing of irrigation. Soybean yield with 4 irrigations alone was nearly same as 5 irrigations,
Reference Calvache and Reichardt (1999) Yavuz (1993) Craciun and Craciun (1999)
Madanoglu (1977)
if the timing of irrigation could be synchronised with growth stages giving the highest yield response. Conversely, the yield might have been reduced if the proper timing was missed even if one would apply supposedly the same amount of irrigation. The soybean yield was reduced nearly 30% when irrigation at vegetation stage replaced irrigation at late flowering stage although in both situations 4 irrigations were applied (Figure 2).
-1
SOYBEAN YIELD, (t ha )
5 4 3 2
V(3) F(2,3) F(2,3) LSD 0.05 F(3) V(3) Y(1,2) V(3) Y(1,2) V(3) F(1,2) F(1) V(3) Y(1,2) F(1,2) Y(1,2) Y(2) F(1,2) Y(1,2)
1 0 DRY
2
(246)
(500-535)
3 (539-566)
4 (602-662)
5 (711-720)
FULL (785 mm)
IRRIGATION NUMBER Figure 2. Effects of deficit irrigation programs on soybean yield. Numbers in parenthesis show range of seasonal evapotranspiration. The letters V, F and Y designate growth stages of soybean when it is irrigated at vegetative, flowering and the yield formation stages, respectively. The numbers from 1 to 3, under a given growth stage, correspond to sub-stages from early to late. (Data is from Tulucu et al., 1991)
Table 2. Crop response factors for major field crops when yield reduction is proportionally less than relative evapotranspiration deficit, imposed during specific growth stages (Kirda, 2002)
ky
Irrigation method
Reference
0.57 0.87
Furrow
Calvache and Reichardt (1999)
0.99
Sprinkler
Bud formation; Flowering
0.75 0.48
Check Furrow
Prieto and Angueira (1999)
Boll formation; Flowering; Vegetation
0.46 0.67 0.88
Furrow
Anac et al. (1999)
Groundnut
Flowering
0.74
Furrow
Ahmad (1999)
Soybean
Vegetative
0.58
Furrow
Kirda et al. (1999)
Vegetative and yielding
0.83
Furrow
Karaata (1991)
Furrow
Bazza and Tayaa(1999)
Crop Common bean
Cotton
Sunflower
Sugar beet
Sugar cane
Growth stage when stress was imposed Vegetative; Yield formation Flowering and yield formation
Yield formation and ripening; Vegetative and yield formation
Bastug (1987)
0.74 0.64
Tillering
0.40
Furrow
Pene and Edi (1999)
Potato
Vegetative; Flowering; Tuber formation
0.40 0.33 0.46
Furrow
Iqbal et al. (1999)
Wheat
Flowering and grain filling
0.39
Basin
Waheed et al. (1999)
4 Conclusions Irrigated agriculture has to continue expanding to cope with increasing food and fiber
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Crop Yield Response to Deficit Irrigation
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Stegman, E.C., Schatz, B.G. and Gardner, J.C. 1990. Yield sensitivities of short season soybeans to irrigation management. Irrigation Science 11: 111-119. Stirling, C.M., Ong, C.K., Black, C.R. 1989. The response of groundnut (Arachis hypogaea L.) to timing of irrigation. Journal of Experimental Botany 40: 1145-1153. Tanji, K. K.1990 (ed.) Agricultural Salinity Assessment and Management. ASCE Manuals and Reports on Engineering Practice No. 71, New York, N.Y. pp 619. Thomas, J.C., Brown, K.W. and Jordan, J.R. 1976. Stomatal response to leaf water potential as affected by preconditioning water stress in the field. Agronomy Journal 68: 706-708. Todd, D.E. 1970. The Water Encyclopedia. Water Information Centre, Port Washington, N.Y. pp 559. Trebejo, I. and Midmore, D.J. 1990.Effects of water stress on potato growth, yield and water use in a hot and cool tropical climate. Journal of Agricultural Science 114: 321-334. Tulucu, K., Kirda, C., Kumova, Y. 1991. Water production function of soybean under limited water supply conditions. Doga-Tr. J. Agriculture and Forestry, 15: 814-826. Van Iersel, M.W., Oosterhuis, M.D. 1996. Drought effects on water relations of cotton fruits, bracts, and leaves during ontogeny. Environmental and Experimental Botany 36: 51-59. Waheed, R.A., Naqvi, H.H., Tahir, G.R. and Naqvi, S.H.M. 1999. Some studies on preplanned controlled soil moisture irrigation scheduling of field crops. In: Crop Yield Response to Deficit Irrigation, C. Kirda, P. Moutonnet, C. Hera, D.R. Nielsen (eds.). Kluwer Academic Publishers, Dordrecht, The Netherlands. Winter, S.R. 1980. Suitability of sugar beets for limited irrigation in semi-arid climate. Agronomy Journal 72: 649-653. Yavuz, M.Y. 1993. Farkli Sulama Yontemlerinin Pamukta Verim ve su Kullanimina Etkileri (Ph.D. Thesis, Turkish). Cukurova University, Faculty of Agriculture, Adana, Turkey. Zhang, J., Sui, X., Li, B., Su, B., Li, J., Zhou, D. 1998. An improved water-use efficiency for winter wheat grown under reduced irrigation. Field Crops Res. 59: 91-98. Ziska, L.H. and Hall, A.E. 1983. Seed yields and water use of cowpeas (Vigna unguiculata L. Walp.) subjected to planned water deficit irrigation. Irrigation Science 3: 237-245.
Remotely-sensed canopy temperatures used for irrigation timing linked to crop water stress index (CWSI) Angela Anda
Abstract We used the canopy and air temperature differential to calculate the Crop Water Stress Index (CWSI) of maize at Keszthely, Hungary over the past fourteen years. Our objective was twofold. First, we wanted to determine if the CWSI could be used to determine when irrigation water should be applied to maize under Hungarian weather conditions. Second, we wanted to know what influence N had on the CWSI. The experiment included two levels of N fertilization and three water treatments: fully watered treatment, irrigated treatment, and non-irrigated control. Canopy temperatures were measured using an infrared thermometer. Relevant meteorological and plant data were also collected. We concluded that during humid years, there is no need to irrigate maize in Hungary. In hot, dry years the CWSI is a useful tool for determining irrigation timing. The amount of applied nitrogen seemed to be a basic determinant of canopy temperature. Additional research needs to be done to learn more about the effect of stressors such as disease or plant nutrition on the CWSI.
Key words: CWSI; maize; canopy temperatures; nitrogen E-mail:
[email protected]
1
Introduction
Two different types of stress indices have been used to quantify plant-water relations over the past several decades. The first type of stress index is based on the combined energy balanceaerodynamic relation (Penman 1948) re-written with surface temperature as a function of net radiation and vapour pressure deficit ( 1981). The second category of stress index comprises the empirical approach of . (1981). These methods have been examined in detail by many authors. Both approaches emphasize the canopy and air temperature differential as a measure of plant water stress. Canopy temperature should be a useful factor in irrigation timing, because meteorological and soil factors indicate when plants may be stressed (Jackson, 1982). A number of researchers have reported on difficulties of CWSI use in humid and semi-humid climates such as changeable radiation and variation 1991; Wanjura and in wind speed (Svendsen Upjohn, 1997; Kumar et al , 1999; Anda, 2001a). To improve the application of the canopy temperature based indices under humid conditions, Jones (1999) suggested adding the leaf conductance of a reference surface. He found the wet leaves to be particularly convenient for this purpose. The CWSI is a commonly applied tool in 1981; irrigation timing for maize (Gardner Clawson and Blad, 1982; Keener and Kirchner,
. 1990; Pennington and 1983; Jensen . 2000; Anda, Heatherly, 1989; Abraham 2001b; Anda, 2002). However, few studies have included the influence of factors such as nutrition or abundant soil water. The aim of this study was to investigate the use of the CWSI for irrigation timing under Hungarian weather conditions at two levels of nitrogen fertilization and three levels of water additions. This paper is a summary of the results. A more detailed description of the experiment can be obtained from the cited papers.
2
Materials and methods
2.1 Theoretical consideration of the CWSI after Jackson (1982) The basic energy balance for plants is:
Rn ? H ? ? E ? G ,
?W m ? ?2
?1?
where Rn: net radiation [W m ], H and ? E: sensible and latent heat fluxes [W m-2], ? : is the latent heat of vaporisation of water [J kg-1 water], E: transpiration intensity [J s-1 m-2], G: heat flux into the ground [W m-2]. Though soil heat flux is judged negligible, being less than 10 % of total net radiation, and is frequently omitted. Monteith (1973) described each component of Equation (1) and its corresponding assumptions in detail. At non-limiting water levels, plants will transpire at the potential rate (potential evapotranspiration, PET). When water in the soil is inadequate, the transpiration decreases below the potential rate (actual evapotranspiration, ET). A -2
measure of the ratio of actual to potential evapotranspiration results in an index (CWSI) that reflects plant water status. Expressing the components of Equation (1), and solving for ? E yields the well-known Penman-Monteith equation for ET, in terms of canopy (rc, s m-1) and aerodynamic (ra, s m-1) resistances:
? Rn ? ? c p ?es ?Tc ?? e? / ra
?E ?
? ? ? ?1 ? rc / ra ?
Idso et al Idso et al c
a
?2?
,
where es(Tc) difference in saturation and actual vapour concentrations of the air [hPa], ? : psychrometric constant [hPa K-1], cp: heat capacity of air [J kg-1 K-1], ? : air density [kg m-3], ? : slope of saturated vapour pressure-temperature -1
rc
?E
? Ep
rc
ET ? ?? ? PET ? ? ? ?1 ? rc / ra ?
CWSI ? 1 ?
rc
rcp
Figure 1 Relationship between canopy and air temperature difference (Tc-Ta) vs. vapor pressure deficit (VPD) showing how to calculate the CWSI after Idso et al. (1981).
?3?
ET ? ?1 ? rc / ra ?? ? * ? PET ? ? ? ?1 ? rc / ra ?
?4?
r ? r R / ?? c ?? ?T ? T ??? ? ? ?? ?e ?T ?? e ? ? r ? ?T ? T ?? r R / ?? c ?
?
c
? = ?*
?5?
?
a
rc
? * ? ? ?1 ? rcp / ra ?
rc ? ?
?6?
2.2 Brief description of the experiment
ra,H
ra,W
ra
? ? -1
? E ? ?ra , w ? rc ? ? H ra
?7?
2
ra,W: and the available water capacity was 210 mm m . A drought tolerant, commercially grown dent variety
of maize (Norma SC (FAO 380)) was grown. Standard agronomic practices for optimum maize production in the local area were followed. In most years, the maize was planted at the end of April or in early May. After emergence, plant density was hand-thinned to 7.0 plants m . In the experiment, we simulated three different watering levels: 1) unlimited water supply provided from the bottom by the lysimeter, 2) rain-fed plants (control), 3) irrigation water added by drip irrigation when the CWSI exceeded the limiting value of 0.25 (Anda, 2002). The original value of 0.2 was determined empirically by Jackson (1982). We corrected it by measurements carried out locally. The amount of water applied per irrigation was between 20 and 40 mm. The experiment also included two different N levels: 1) 0 N (control) and 2) 100 kg N ha . Meteorological elements were collected at a nearby weather station (QLC-50). After canopy closure, plant surface temperatures for CWSI determinations were measured with an infrared thermometer (RAYNGER II) ?
3 Results and discussion 3.1 Results in humid seasons and influence of nitrogen on CWSI
1997
1997 6 5 4 3 2 1 0
CWSIx10
5 4 3 2
Month.day P
8.28
8.18
8.8
7.29
0 7.19
8-28
8-18
8-8
7-29
1
7-19
CWSIx10
6
Month.day
PC
Figure 2 Seasonal variation of tenfold CWSI values at two nitrogen levels during the humid season of 1997. PC treatment without sign, and P with nitrogen fertilization
ET N
PN
Figure 3 Yearly change in CWSI measured in lysimeter growing chambers (ET) and for rain-fed conditions (P)
Even in humid seasons, N-shortage increased the values of CWSI significantly. The stress on plots with N-fertilizer (P) additions was approximately half of that for plots that did not receive N fertilizer (PC). The effect of N on CWSI was higher in the second half of the growing season (Figure 2). These results indicate that several factors affect the CWSI of plants growing in the field. The summer of 1997 was wet, especially in June and July, when the amount of rainfall was 28% higher than the norm. The CWSI of rainfed plots never reached the limiting value of 0.25 as shown in Figure 3, when the nitrogen supply was close to optimum level (100 kg N ha-1) in both water treatments. In contrast, we observed that CWSI values were relatively high in the lysimeters. At the beginning of the season, this occurred on days just following precipitation, but later it occurred continuously. Probably the water inside the closed chambers ousted the air from the soil and the plants developed stress because of water-logged conditions.
3.2 Results during arid seasons In general, arid years were characterized by both a shortage of rainfall and relatively high air temperatures. This resulted in an increase in CWSI values compared to humid years. Lack of N increased the seasonal mean of the CWSI by 116% in rain-fed plots in arid years compared to humid years. The typical variation in CWSI during an arid year is presented using data from 1998 (Figure 4). Surprisingly, the CWSI was similar for both levels of N in the rain-fed plots. The stress index in these two fertilizer treatments might have been influenced by the close connection between watering and nutrition level of plants. In order to simplify the figure, only indices determined for rain-fed plots are presented. In 1998, irrigation decreased the yearly mean of CWSI by 131% compared to the CWSI of non-irrigated control plots. Irrigation also increased yield by 14.5% during this dry and warm year.
20
2
10
0
0
Prec.
PC
PN
24.aug
4
14.aug
30
04.aug
6
25 july
40
15 july
8
5 july
50
25 jun
10
Precipitation, mm
CWSIX10
1998
PNI
Figure 4 CWSI for maize during an arid summer of 1998. Abbreviation C and N shows the lack and 100 kg N ha-1 nitrogen, respectively. The watering levels were as follows: irrigated plots PNI, non-irrigated plots: PN. The arrows indicate the time of irrigation
3.3 Canopy temperature observations The governing factors of the CWSI, the canopy and air temperature differentials, and canopy temperature alone were also studied. In the non-irrigated control, the canopy and air temperature difference reached a maximum of 9-
4 Conclusions
variations in the most important plant parameters including LAI and yield. The results indicate that the CWSI may be a useful tool for determining irrigation timing under Hungarian climatic conditions, but only when the weather is hot dry and during temperate humid summers there is no need for irrigation. In semi-humid weather the yield surplus of maize produced by irrigation is not enough to cover the extra costs of watering. In arid
seasons, the use of the CWSI provided a way to maximize economic return by applying only the amount of water that was actually needed by the crop. We conclude that attention should be paid to the effect of non-water related stressors such as plant diseases and inadequate nutrition on CWSI. Neglecting these factors may lead to the over-application irrigation water.
Table 1. Standard deviations of canopy temperature for different N and irrigation levels (1997 and 1998)
Rain-fed
plots
Irrigated
plots
Maize
N use
n
Control
N
N use
n
Control
N
1997
0.182
48
0.278
48
0.139
20
0.382
20
1998
0.300
49
0.410
49
0.208
21
0.398
21
LSD5%: 0.11 Table 2. CWSI values for maize at the Keszthely Agrometeorological Research Station under different weather conditions between 1989 and 2002
Weather conditions Number of the seasons
ARID 6 Deviation
HUMID 3 from the climatic
? Irrigation necessity
SEMI-HUMID 5 normal
Yes
? No
? Yes ?
10
No
?5
CWSI Change in yield (%)
Acknowledgements
106
References 64 45
74,
(ZEA MAYS L.) 46 73,
24, 12,
water stress indicator. Water Resour. Res. 17, 1133-1138. Jensen, H.E., Svendsen, H, Jensen, S.E., Mogensen, V.O. 1990. Canopy-air temperature of crops grown under different irrigation regimes in a temperature humid climate, Irrig Sci, 11, 181-188. Jones, H.G. 1999. Use of infrared thermometry for estimation of stomatal conductance as a possible aid to irrigation scheduling. Agric. and Forest Meteorol., 95 (3), 139-149. Keener, M.E and Kirchner, P.L. 1983. The use of canopy temperature as an indicator of drought stress in humid regions, Agric. Meteorol. 28, 339-349. Kumar, V.P., Ramakrishna, Y.S., Ramana Rao, B.V., Khandgonda, I.R., Victor, U.S., Srivastava, N.N. and Rao, G.G.S.N. 1999. Assessment of plant-extractable soil water in castor beans (Ricinus communis L.) using infrared thermometry, Agric. Water Management. 39 (1), 69-83.
Monteith, J.L. 1973. Principles of Environmental Physics. Edward Arnold Publishers, London. Penman, H. L., 1948. Natural evaporation from open water, bare soil and grass. Proc. of the Royal Soc. A, 193, 120-145. Pennington, D.A. and Heatherly L. 1989. Effects of changing solar radiation on canopy-air temperature of cotton and soybean. Agric. Forest Meteorol. 46, 1-14. Svendsen, H., Jensen, H.E., Jensen, S.E., Mogensen, V.O. 1991. Crop Canopy Temperature and Meteorological Conditions. Proc. From the Workshop on Remote Sensing. (Thomson, A.-Jensen, A.-Jensen, H. E. eds.), Sastrup Castle, Grena, May 6-7, Denmark. Wanjura, D. F. and Upchurch, D. R. 1997. Accounting for humidity in canopy-temperature-controlled irrigation scheduling, Agric. Water Management. 34 (3), 217-231.
Improving water use efficiency based on comparative sensitivity of soybean stomatal conductance and photosynthesis to soil drying Fulai Liu 1, Mathias N. Andersen2 and Christian R. Jensen1 1
The Royal Veterinary and Agricultural University, Department of Agricultural Sciences, Laboratory for
2
Abstract The sensitivity of stomatal conductance and photosynthesis to stress was examined for soybean L. Merr.) during progressive soil drying, to suggest improvement to water use efficiency. ( Soybeans were grown in pots in a climate-controlled greenhouse. Stomatal conductance ( s), photosynthetic rate ( max), photosynthetic water use efficiency (WUEAmax/gs), root water potential (? r), xylem sap ABA concentration ([ABA]xylem), and leaf turgor (? pl) were determined in well-watered and drought-stressed plants. Measures of these biophysical parameters for drought-stressed plants were expressed relative to those of the fully watered controls. As soil dried, relative s, relative max, and relative ? pl were about 1.0 until the fraction of transpirable soil water (FTSW) decreased to 0.64 ? 0.04, 0.51 ? 0.03, and 0.25 ? 0.03, respectively. Relative [ABA]xylem started to increase at FTSW = 0.65 and increased linearly with decreasing ? r. Relative s decreased linearly from FTSW = 1.0 to about 0.30 with increasing relative [ABA]xylem; when FTSW < 0.30, it decreased further to 0.10 and was linearly correlated with decreasing relative ? pl. The relationship between relative s and relative 2 = 0.98). Relative WUEAmax/gs was around 1.0 max was well represented by a logarithmic function ( for FTSW > 0.60-0.65, thereafter it increased exponentially and reached a peak at FTSW = 0.25-0.30. As FTSW approached zero then WUEAmax/gs declined linearly to less than 1.0. The results indicate that at mild soil water deficits, s is controlled primarily by root-originated ABA; and ? pl significantly affects s only at severe soil water deficits. As a result of greater maintenance of max than s during soil drying, WUEAmax/gs is improved in a range of soil water deficits (FTSW from 0.64 to 0.10). Key words: Soybean; soil water deficits; stomatal conductance; photosynthesis; water use efficiency
Email:
[email protected] sending chemical signals to the shoot to elicit several adaptive responses, including decrease in leaf expansion growth and stomatal closure, and this can occur without any change in shoot water relations could be detected (Davies and Zhang, 1991; Jackson, 1993). Accumulated evidence suggests that drought-induced increase in [ABA]xylem acts as a major signaling molecule involving in the response of plants to drought stress (Davies and Zhang, 1991; Tardieu and Davies, 1993). A common functional mode of ABA signaling in drought-stressed plants has been proposed: as the soil dries, ABA is produced in the root tips and is transported into the xylem via the transpiration stream reaching to the leaf where it reduces stomatal conductance (Dodd and Davies, , 1998; Bahrun , 2002; Liu 1996; Ali , 2003). As a consequence, the stomatal aperture can be regulated so that a partial closure of stomata at a certain level of soil water deficit may lead to an increase in WUEAmax/gs. To take advantage of this kind of plant response, irrigation techniques aimed to improve plant water use efficiency, such
1 Introduction Water scarcity is a major factor limiting agricultural production all over the world (e.g. Turner, 1986). For sustainable agricultural development, irrigation practices must become more efficient (Turner, 1997). During the last two decades, a great deal of work has been done to try to improve plant water use efficiency (Turner, 1997). A lot of research attention has focused on stomata because they occupy a central position in the pathways for both the loss of water from plants and the intake of CO2. Photosynthetic water use efficiency (WUEAmax/gs) can be defined as the ratio between the rate of photosynthesis ( max) and the rate of stomatal conductance for water vapour ( s). Theoretically, WUEAmax/gs may be improved by partial closure of stomata so that the internal CO2 concentration ( i) is just sufficient for saturation of photosynthesis while the rate of water loss had been significantly lowered. It is well recognized that plants can sense the water availability around the roots and respond by 1
et al.
n
f
n f
1.0
2 Materials and methods
0.8 FTSW
2.1 Plant material and growing conditions 0.6 0.4
Glycine max 0.2
Well-watered Droughted
0.0 0
3
6
9
12
15
18
21
24
Days after imposition of stress
?
?
?
-2
Figure 1 Development of the fraction of transpirable soil water (FTSW) over time for well-watered and drought-stressed pots in which soybeans were grown. FTSW was calculated using Eqn 1. Error bars reprent standard error of the means (s.e.m.) (n = 8)
-1
Bradyrhizobium japonicum
2.3 Leaf gas exchange and leaf turgor measurements
2.2 Water treatments
2
?
2
?
Inc., Logan, UT, USA) connected to a datalogger (CR7X, Campbell Scientific, Logan, Utah) interfaced to a computer. The system allowed graphic readout of the 20 min interval measurements to ascertain that water vapour equilibrium was reached before the final reading was taken (2 h equilibrium time). Leaf turgor was calculated as the difference between water potential and osmotic potential.
A Ci
A
Ci r2
2.4 Root water potential determination and collection of xylem sap Xylem sap was collected by pressurizing the potted plant in a Scholander type pressure chamber. The entire pot was sealed in the pressure chamber and the shoot was de-topped 15-20 cm from the stem base. With the stem stump protruding outside the chamber, pressure was applied until the root water potential was equalised. The cut surface was cleaned with pure water and dried with blotting paper. A piece of silicon tube was then placed on the stump so that the epidermis was not damaged and no leaking occurred. The top of the silicon tube was connected to the capillary top of an Eppendorf glass pipette. A small diameter silicon tube collected the sap through the capillary let into an Eppendorf-vial wrapped with aluminum foil. Afterwards, the pressure of the chamber was increased gradually until it equalled the leaf water potential of the plant, 0.5-1.0 mL of sap was collected over 5-10 min in well-watered and 20-30 min in drought-stressed plants. The sap was ? immediately stored at
t
3 Results 3.1 Development of biophysical parameters in well-watered and droughted plants gs Amax Amax/gs ? r ?? pl xylem -2 -1 -2 -1 ? -1 ? 2 2 -1
gs
Amax
Amax/gs
?r
2.5 Abscisic acid assay
?? pl
?? pl
?r
xylem
et al. 3.2 Relationships between the relative values of biophysical parameters and FTSW gs Amax ?? pl
2.6 Data analysis and statistics Amax
Amax/gs
?r
xylem
?r
? pl
gs gs Amax
xylem
?? pl
Amax/gs
gs Amax
?? pl
Amax/gs
Ci ? A?
?
Amax/gs
Ci
? Ci
3
?r
xylem
0.50, when FTSW < 0.50, it increased exponentially (Figure 3d, e). The relationship between relative gs and relative Amax was well represented by a logarithmic function (r2 = 0.98) (Figure 4).
Table 1 Soil-water thresholds (Ci) for stomatal conductance (gs), photosynthetic rate (Amax), and leaf turgor ?? pl) of soybean grown in a climate-regulated glasshouse. Ci were expressed as the fraction of transpirable soil water (FTSW) at which the relative values of the biophysical parameters started to decline from 1
3.3 Root and shoot factors in the control of stomatal conductance
There was a clear linear relationship between [ABA]xylem and ? r (Figure 5). Relative gs decreased linearly from 1.0 to about 0.30 with increasing relative [ABA]xylem (Figure 6a); for drier conditions, it decreased further to about 0.10 and was linearly correlated with decreasing relative ? pl (Figure 6b).
Ci ? s.e.m.
r2
Stomatal conductance (gs)
0.64 ? 0.04
0.96
Photosynthetic rate (Amax)
0.51 ? 0.03
0.95
Leaf turgor ?? pl)
0.25 ? 0.03
0.87
0.5
a
Well-watered Droughted
d
0.0
0.6
-0.5
(MPa)
g (mol m
s )
0.8
Biophysical parameters
0.4
-1.0 -1.5
0.2
-2.0 -2.5
(pmol ml )
b
10 0
[ABA]
( mol m
20
A
30
( ? mol CO mol H O )
6000 4000 2000 0
c
f
0.8
90 60
0.6 0.4
30
WUE
e
8000
(MPa)
s )
0.0
0.2
0
0.0
0
3
6 9 12 15 18 21 Days after imposition of stress
24
0
3
6 9 12 15 18 21 Days after imposition of stress
24
Figure 2 Development of stomatal conductance (gs) (a), photosynthetic rate (Amax) (b), photosynthetic water use efficiency (WUEAmax/gs) (c), root water potential (? r) (d), xylem sap ABA concentration ([ABA]xylem) (e), and leaf turgor ? pl) (f) of well-watered and drought-stressed soybeans during the experimental period. Bars indicate s.e.m. (n = 4)
4
4
1993), maize cultivars (0.39-0.60, Ray and Sinclair 1997), chickpea (0.34, Soltani et al. 2000) and vegetable amaranth (0.35-0.60, Liu and
Discussion and Conclusions
This study was initiated to investigate the physiological mechanisms that may be involved in the control of stomatal aperture of soybean during soil drying, and to test the hypothesis that water use efficiency of soybean could be improved under certain levels of drought stress. We quantified the responses of several plant processes to soil drying on a common base, viz. FTSW in the pots where plants were grown. The sensitivity of gs, Amax, and ? pl to soil drying was investigated by comparing their soil-water thresholds; and the regulatory pattern of chemical and hydraulic signals on stomatal conductance was suggested. The soil-water threshold for g s (0.64 ? 0.04; Figure 3a; Table 1) in soybean observed herein was greater than the values reported for other crops, e.g., sunflower (0.40, Tardieu and Davies
gs
300
a
1.0
250
0.8
200
0.6 0.4 0.2 0.0
100
e
50
Relative [ABA]
Relative A
d
150
0
b
0.8 0.6 0.4 0.2
40 30 20 10 0
c
f
1.0
2.0
0.8
1.5
Relative
Relative WUE
A max
50
1.0
0.0
Amax
et al.
Relative
Relative g
1.2
?
1.0 0.5
0.6 0.4 0.2
0.0
0.0
1.0
0.8
0.6 0.4 FTSW
0.2
0.0
1.0
0.8
0.6 0.4 FTSW
0.2
0.0
Figure 3 Relationships between relative stomatal conductance (relative gs) (a), relative photosynthetic rate (relative Amax) (b), relative photosynthetic water use efficiency (relative WUEAmax/gs) (c), relative root water potential (relative ? r) (d), relative xylem sap ABA concentration (relative [ABA]xylem) (e), relative leaf turgot (relative ? pl) (f) and the fraction of transpirable soil water (FTSW) for soybean grown in a climiate-controlled glasshouse. Each point represents the ratio between the mean of drought-stressed plants and the mean of wellwatered plants. Bars indicate s.e.m. (n = 4). Curves in a, b, f are fitted by linear-plateau functions (Eqn 2); the curve in d and e fitted by a linear function for the first four points (from left to right) and an exponential function for the last five points. Curve in c is drawn by hand
5
et al. gs Amax
gs Amax gs
Amax
?r
xylem
et al.
gs
Amax
?r
Amax/gs
?r
xylem
?r
Amax/gs
et al. gs
? pl
et al.
et al.
gs
? pl
(pmol ml )
10000 8000
gs
6000
[ABA]
4000
Y = -3.72X - 0.43 r = 0.93**
2000
?r
0
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
gs et al. gs
?r
-3.0
? (MPa)
et al.
Figure 4 Linear relationship between root water potential (? r) and xylem sap ABA concentration ([ABA]xylem) in soybeans grown in a drying soil. Bars indicate s.e.m. (n = 4)
?r
Amax/gs
Amax
1.2 1.0
Relative A
0.8
Amax
0.6 0.4
Y = 0.38Ln(X) + 0.97
0.2
r = 0.98**
gs Amax/gs
gs
0.0
1.2
1.0
0.8 0.6 0.4 Relative g
0.2
0.0
gs
Amax/gs
Figure 5 Logarithmic relationship between relative gs and relative Amax in soybean grown in a drying soil. Bars indicate s.e.m. (n = 4)
6
Amax
?? pl gs
1.2 a
b
1.0
Y 2 = 0.27X + 0.06
Y1 = -0.20X + 1.23
r 2 = 0.92***
Relative g s
2
r = 0.96**
0.8 0.6 0.4 0.2 0.0 0.0
1.0
2.0
3.0
4.0
5.0
1.2
1.0
0.8
0.6
Relative ?
Relative [ABA] xy lem
0.4
0.2
0.0
pl
Figure 6 Relative stomatal conductance (gs) expressed as a linear function of relative xylem sap ABA concentration ([ABA]xylem) (a) and of relative leaf turgor (? pl) (b) of soybeans grown under a drying soil. Bars indicate s.e.m. (n = 4)
J. Exp. Bot.
Acknowledgements
53,
We give thanks to: Dr Tommy Carter, North Carolina State University, USDA, ARS, for the soybean seeds and Dr Steven Quarrie, John Innes Centre, UK, for the antibody to ABA. The technical assistance of Britta Skov
Ann. Rev. Plant Physiol. Plant Mol. Biol. 42,
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Kochler, M. 2000. Analyse und Modellierung der Anpassungsreaktionen von Blumenkohl (Brassica oleracea L. botrytis) an eine limitierte Wasserversorgung. PhD thesis. Department of Horticulture, University of Hannover. Liu, F., Jensen, C.R., Andersen, M.N. 2003. Hydraulic and chemical signals in the control of leaf expansion and stomatal conductance in soybean exposed to drought stress. Funct. Plant Biol. 30, 65-73.
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Adv. Agron. 58,
8
High wheat water use efficiency of limited water in semi-arid areas Xiping Deng 1, 2, Lun Shan 1, Shaozhong Kang 2, Inanaga Shinobu3 and M. Elfatih K.Ali3,4 1
Institute of Soil and Water Conservation, Chinese Academy of Sciences, Shaanxi 712100, China 2Northwest Sci-Tech University of Agriculture and Forestry, Shaanxi 712100, China 3 Arid Land Research Center, Tottori University, Hamasaka 1390, Tottori 680, Japan 4 El-Obeid Research Station, Agricultural Research Corporation, P.O. Box 429, El-Obeid, Sudan
Abstract A review is presented of crop physiological adaptation and benefits associated with deficit and variable water conditions. It is widely accepted that ABA mediates general adaptive responses to drought. However, there is evidence suggesting that additional signals are involved in this process. Breeding of drought resistance shows that a high yield potential is negatively associated with certain drought adaptive traits in wheat. Such a negative association may put a limit on raising potential yield as means for improving actual yield under semiarid conditions. For a relatively determinate target stress environment and with stable genotype×environment interaction, the probability for achieving progress is high. This approach will be possible only after we learn more about the physiology and genetics of wheat plant responses to water stress and their interactions. The difficulties encountered by molecular biologists in attempting to improve crop drought resistance are due to our ignorance in agronomy and crop physiology and not to lack of knowledge or technical expertise in molecular biology.
Key words: Semiarid conditions, wheat origination, physiological adaptation, yield improvement E-mail:
[email protected].
1 Introduction 1.1 General Drought is a worldwide problem and water shortage is now becoming the number one ecological predicament facing humans. About 40% of the land surface in the world is arid and semiarid. This includes USA, Canada, former Soviet Union, India, Australia, China, Middle East and some African countries, which are characterized as having limited water for conventional rain fed agriculture (Stewart, 1988; Parr et al., 1990; UNEP, 1997; Gamo, 1999). Because of drought, average crop yields throughout the world annually approach only 30% of maximum attainable yields. Water stress is the major factor preventing realization of maximum yields, with water-deficits causing the greatest reductions (Brengle, 1982; Schillinger et al., 1999). Yet, in the world, millions of people live in such regions, and if current trends in population increase continue, there will soon be millions more. These people must eat, and the wisest course for them is to produce their own food (Dennis and Fry, 1992).
Periods of drought alternating with short periods of wet conditions are common to many semiarid areas of the world (Richards et al. 2002, Shan 2002). Wheat plant response to this water deficit and variable environments is complex, including variable frequency of droughts and wet periods; variable degrees of drought; speed of onset of drought conditions; and varying patterns of soil water deficit and/or atmospheric water deficit (Deng et al. 2003). In many cases the most suitable technologies for a particular region may be that already developed by the local farmers. In some cases it will be difficult to improve on local technologies, but at times even simple and inexpensive innovations may be almost revolutionary. This technical note suggests that one must begin to improve traditional agriculture in arid and semiarid zones by learning what is already there. 1.2 Farming practices in semiarid area Dryland farming is the profitable production of useful crops, without irrigation, on lands that receive annual rainfall of 500 mm or less. When
annual precipitation is below 500 mm, the methods of dryland farming are usually indispensable (Monteith, 1990). In these regions a major challenge is to manage water appropriately. The purpose of such management is to obtain water, conserve it, use it efficiently, while avoiding damage to crops (Deng et al, 2002a). Farm practices must conserve and use available rainfall efficiently. To obtain maximum storage under any rainfall condition, soil must absorb as much water as possible when it rains and losses due to evaporation or transpiration must be kept to a minimum. 1.2.1 Tillage All tillage and plantings run across the slope. Such ridges impede downward movement of water. Water in the soil exists as a continuous film surrounding each grain. Tillage creates a rough cloddy surface that lengthens the time necessary for rain to break down clods and seal the surface. For seed bed preparation in general, small seeds require a finer bed than large seeds (Unger, 1992). After harvest, a stubble mulch is created on the soil surface. Such material not only prevents raindrops from directly striking the soil, but also impedes the flow of water down the slope, increasing the absorption time (Moldenhauer, 1959; Yadav, 1974; Ross et al., 1985; Jama and Nair, 1996). In semiarid regions, after harvest time the soil is generally too dry for plowing. Yet if the field is left uncultivated, this dry condition may become even worse and weeds will also grow and produce seeds. So fields should be harrowed or chiseled and crop residues left to form a stubble mulch to absorb/retain moisture (Gregory et al., 2000). 1.2.2 Mulch Water easily enters porous soil and, as it seeps downward, becomes absorbed as films of water around the soil particles. This film of water in the soil is known as capillary water and it is the source of water for the plants (Moldenhauer, 1959). Stubble mulching aims at disrupting the soil drying process by protecting the soil surface at all times either with a growing crop or with crop residues left on the surface during fallow. The first benefit of a stubble mulch is that wind speed is reduced at the surface by up to 99%, losses due to evaporation significantly reducing (Yadav, 1974). In addition, crop and weed residues can improve water penetration and decrease water runoff losses 2 - 6 fold and reduce wind and water erosion 4 - 8 fold relative to a bare fallow field. To obtain the benefit of mulching on soil structure without causing temporary de-nitrification, mulch can be
composted before adding it to the soil. Rapid bacterial action in the tropics makes composting less beneficial than in temperate climates but may still be worthwhile (Mandal and Ghosh, 1984; Ross et al., 1985; Barros and Hanks, 1993; Jama and Nair, 1996). Stubble should not be immediately covered and incorporated into soil unless rodent or insect infestation is heavy (and even then burning should be considered). It has been well demonstrated that it is normally impossible to raise the soil organic matter content in areas where temperatures are high for long periods. When moisture is present, the rates of oxidation are extremely high and incorporated organic matter is quickly lost. The benefits of decomposition, as experienced in more temperate
1.2.3 Planting Density
1.2.4 Crop Rotation
1.2.5 Moisture Conservation
with moisture requirements as the main consideration. For a given set of climatic conditions, a crop may be described as either moisture dissipating or conserving. After harvest of a moisture-conserving crop, the soil contains more moisture than at planting. This conserved moisture can help guarantee the success of the succeeding crop. Crops which are sown in rows so that intertillage and dirt mulching can be practiced tend to be moisture conserving. Under sowing may also assist in conservation. Moisture may be insufficient to grow a crop and conserve enough water for the succeeding crop. In such a case, it is necessary to use a dirt and stubble mulched fallow in the rotation. If annual rainfall is 10 to 15 inches (250 to 375 mm), this practice will be needed at least every other year; and if rainfall is 15 to 20 inches (375-500 mm), it will be needed at least once in every three years. A dense ground cover tends to resist erosion much better than crops which are intertilled or tend to be moisture conserving. Loss of soil due to erosion is a significant dry farming problem and erosion controlling crops should be included in a rotation, preferably in a strip cropping mode (Williams et al., 1983). 1.2.6 Soil Nutrients and Structure When related crops are successively planted specific soil minerals and nutrients are withdrawn faster than they can be replaced by microbial action or weathering. This selective depletion causes a soil to be "worn out" quickly. Simple rotation of crops makes depletion more uniform so that soils "wear out" more slowly. Planting of legumes (such as gram or groundnut or alfalfa) with their nitrogen fixing capabilities tends to restore soil fertility. Use of green manure (plowing under of a green crop, such as alfalfa, rather than harvesting) can also improve soil fertility and texture but benefits may be short lived in the tropics and difficult for Third World farmers. Planting of any deep or extensively rooted plants (such as grasses, alfalfa.) tends to improve soil structure and draw subsoil nutrients to the surface like a natural fallow and can increase pasturage during dry periods. Crops like cassava, which require relatively little soil nutrients, may also be grown in rotation or when soil is almost worn out. In general, the rainfall amounts required at higher altitudes can be slightly lower than expected. The potential evapotranspiration does not change much during the rainy seasons for tropics and subtropics. After a dry season, sowing starts when accumulated rainfall exceeds 60 mm in less than 30 days. The maximum moisture
storage within a soil at field capacity is approximately 100-150 mm. When a crop is sown in a soil at field capacity, much less rainfall is required during the growing season. Necessary rainfall in the month of flowering is for the 30-day period from 20 days before 50% flowering to 10 days after 50% flowering. If the crop is to be harvested by a combine, rainfall during harvest should be less than 120 mm/month (and much less than that if there are rains in the late morning).
2 Environmental limitations on wheat yield 2.1 Wheat origin from semiarid area Wheat is a common name for cereal grasses of a genus of the grass family, cultivated for food since prehistoric times by the peoples of the temperate zones and now the most important grain crop of those regions. Wheat is a tall, annual plant attaining an average height of 1.2 m. The leaves, which resemble those of other grasses, appear early and are followed by slender stalks terminating in spikes, or so-called ears, of grain. Species of wheat are classified according to the number of chromosomes found in the vegetative cell. They are divided into three series: the diploid, or einkorn, containing 14 chromosomes; the tetraploid, or emmer, containing 28 chromosomes; and the hexaploid, containing 42 chromosomes (Gill et al., 1991). Wheat species crossbreed relatively frequently in nature (Harris, 1990). Selection of the best varieties for domestication took place over many centuries in many regions (Li, 1970; Harlan, 1987). Today, only varieties of common, club, and durum wheats are of commercial importance, but other species are still grown to suit local conditions and provide essential stock for formal breeding programs (Talbert et al., 1991). Remains of both emmer and einkorn wheats have been found by archaeologists working on sites in the Middle East dating from the 7th millennium BC. Emmer was grown in predynastic Egypt; in prehistoric Europe it was grown in association with barley and einkorn and club wheats. Bread wheat was identified at a 6th-millennium BC site in southern Turkestan, and a hexaploid wheat was found at Knossos in Crete (Harlan, 1987). 2.2 Wheat distribution and domestication in water limited areas According to the regions in which they are grown, certain types of wheat are chosen for their adaptability to altitude, climate, and yield. The
common wheats grown in China, United States, and Canada are spring and winter wheat, planted either in the spring for summer harvest or in the fall for spring harvest. The color of the grain varies from one type to another; white grains are mostly winter wheats, while red ones are spring wheats. Closely related to the common wheats are the club wheats, which have especially compact spikes, and spelta, in which the glumes (reduced, scale-like leaves) tightly enclose the grains. Durum wheat (Latin durum) is so called because of the hardness of the grain. It is grown in north-central regions of the United States. Compared with rice, all kings of wheat seem distributed in the water limited area. The domestication of wheat occurred in the hilly region of southwestern Asia bordered on one side of the Tigris-Euphrates basin (ancient Mesopotamia) and on the other by the mountains of Iran, Turkey, Syria, and Jordan (Li 1970). This
T. turgidum
℃
Triticum monococcum dicoccoides 2.3 Wheat production in the world
T. sphaerococcum,
aesttivum
℃
manipulated, yield improvement is associated with adaptation to high plant density (Reynolds et al., 1999). Studies have confirmed that the juvenile spike growth phase is critical in determining both grain number and kernel weight (sink) potential. Improving assimilate availability during this stage, perhaps by lengthening its relative duration, may be one way to improve yield potential. Traits that could potentially be exploited for improving assimilate (source) capacity include early vigor, stay-green, leaf-angle and remobilization of stem reserves. Use of alien chromatin is a successful approach for introducing yield-enhancing genes into elite genetic backgrounds. Examples include the 1B/1R chromosome translocation from rye (Secale cereale L.) and more recently the LR19 segment from tall wheatgrass [Agropyron elongatum (Host) P. Beauv.]. Improving the efficiency of early-generation selection may be another strategy for raising yield potential by increasing the probability of identifying physiologically superior lines by techniques such as infrared thermometry and spectral reflectance. 2.4 Wheat adaptability to drought conditions The evaluation of crop genotypes for their adaptability is often performed by means of regression techniques of yields against some environmental index acting as an independent variable. The weakness of these techniques lies in the lack of a direct assessment of a given environment by specific environmental factors. Karamanos and Papatheohari (1999) suggested a new index, the water potential index (WPI), as a measure of the total water stress experienced by any crop in a given environment for a specific time interval. Their results showed that the index is derived from the integral of the course of leaf water potential over time. Its usefulness is demonstrated in evaluations of field-grown bread wheat and faba bean genotypes of contrasting characteristics by yield vs. WPI linear regression analysis. In these
3 Water deficit effects on wheat production 3.1 Drought stress
having its own unique consequences for the growth and yield potential of the stand. Once these stages and influence of the environment on them are understood, informed management and breeding strategies are possible. The following are some of the important developmental
stages
in
winter
wheat
and
the
consequences for yield losses associated with severely limited soil water supplies.
Table 1. Effect of drought stress on wheat growth and yield consequences* Stage of Development Seed Seedling Tillering, Spike Initiation Stem Elongation & Spike Growth Anthesis (flowering) Maturity
Effect of Drought Germination reduced & delayed Increased tiller
Yield Consequences Altered yield components. Reduced yield if less than ca. 1000 plants/m2. Reduced spikes/m2 and yield
Reduced N uptake
Accelerated senescence.
Death of young florets
Reduced grain set and yield
Greater accumulation of soluble stem stem carbohydrates, partially buffers plant against loss of photosynthesis during grain filling. Accelerated senescence Reduced mean grain size Reduced elongation
*After Lafond and Baker, 1986; Navari-Izzo et al., 1989; Pecetti et al., 1992; Deng et al., 2002b. In the past, wheat yield increase has invariably resulted from increased kernel number per unit area with little change in kernel weight (Feil, 1992). Fischer (1985) proposed that kernel number is the resultant of spike dry weight at anthesis (g per unit area), which has increased through breeding, and kernels per unit spike weight, which is unchanged. Spike weight in turn is the product of duration of spike growth phase, crop growth rate and partitioning of dry matter into spike during this phase. Another way to view the effects of water stress on wheat yield potential is to understand yield as a function of its yield components (Table 2)
Table 3. Some plant drought-resistant traits
Table 2. Effect of water stress on wheat yield components
Yield Component Spike Number No. of Grains/ Spike Grain Weight
Important Developmental Stages Seed - Tillering Tillering - Early Grain Filling Anthesis
3.2
Physiological adaptations to water stress
2
2
acceptor in photosynthesis. In the presence of light, Photosystem I (PSI) continues to operate resulting in the production of the reducing compound NADPH. Plants have a very limited capacity to store NADPH. The light reactions involve the splitting of water to produce protons and oxygen free radicals (O2?), hydroxyl radicals (OH?) and singlet oxygen, highly reactive, unstable molecules with unpaired electrons in the outer shell. These can destroy membrane lipids, chlorophyll and proteins unless a receptor (NADP+) for the increased reducing power is present. Evans (1993) noted that photorespiration may be adaptive for plants growing under water stress by regulating reductant and avoiding photochemical damage. Thus efforts to improve crops by eliminating photorespiration might make them less tolerant to water stress and, hence, less adapted to dry regions. Polyamine metabolic level also was linked with water stress (Reggiani et al., 1993).
available. Thus such adaptations would not be beneficial for wheat selected for high yields in more favorable environments (Blum, 1985). It is often suggested that the yields of conventional wheat in dry areas can be improved by introducing "genes for drought tolerance" from its relative species. Crop characteristics like droughttolerance are a likely focus of the new technologies. The adaptations that allow some plants to lose very little water through their leaves in transpiration, transferred to more widely grown crops, could reduce irrigation needs. This strategy of bioengineering drought tolerance into wheat is likely to fail if the trade-offs inherent in many adaptations to drought are not taken into account.
4 Water stress physiology and molecular biology on wheat Wheat plants respond to drought through morphological, physiological, and metabolic
3.3 Morphological Adaptations to Water Stress To cope with prolonged stomatal closure, many wheat varieties have adaptations that function to reduce R(n), the amount of absorbed radiation reaching the photosynthetic tissues, thus alleviating the problems of heat load and the adverse affects of photochemical damage. Interception of solar radiation is reduced by several drought adaptations. Increasing reflectance by the presence of a dense covering of light-colored trichomes (hairs) on the leaf surface, resinous coatings on the foliage, or thick waxy cuticles. A thick cuticle has added advantages, it absorbs ultraviolet radiation, greatly reduces cuticular transpiration and increases disease resistance (by imposing a barrier to fungal and bacterial pathogens). Evans (1993) noted that increased glaucousness (waxy surface) in wheat and barley can increase yields in dryland environments by lowering leaf temperatures and improving water-use efficiency. Some wheat varieties have a high leaf density resulting from production of fibers, sclerenchyma, thick cell walls or the accumulation of silica. Such drought inducible traits is helpful for protecting insects (Philippe et al., 2000). These adaptations favor survival of plants during drought but are associated with reduced photosynthetic rates (Fischer and Turner, 1978; Fitter and Hay, 1987). These morphological adaptations to dry conditions clearly involve tradeoffs. That is, increased light reflectance and increased resistance to H2O diffusion become constraints to photosynthesis and growth when water is readily
modifications occurring in all plant organs. At the cellular level, plant responses to water deficit may result from cell damage, whereas other responses may correspond to adaptive processes. Greater osmotic adjustment may also result in more root growth and an ability to extract additional soil water (Morgan, 1995). However, selection for osmotic adjustment is not easy at the present time, although a novel method to select in the wheat haploid stage has recently been demonstrated (Morgan, 2000). Despite a large number of drought-induced genes being identified in a wide range of wheat varieties, a molecular basis for wheat plant tolerance to water stress remains far from being completely understood (Ingram and Bartels, 1996). Rapid translocation of ABA in shoots via xylem flux and the increase of ABA concentration in wheat plant organs correlates with the major physiological changes that occur during plant response to drought (Zeevaart and Creelman, 1988). It is widely accepted that ABA mediates general adaptive responses to drought. However, there is evidence suggesting that additional signals be involved in this process (Munns and King, 1988; Davies and Zhang, 1991; Munns et al., 1993; Griffiths and Bray, 1996). Six cDNAs corresponding to transcripts up-regulated by water stress were isolated
previously from a drought-tolerant sunflower (Helianthus annuus L.) line, R1 (Ouvrard et al., 1996). Comparison of the steady-state level of transcripts between the R1 line and a closely related drought-sensitive line, S1 has shown that three of those transcripts (HaElip1, HaDhn1 and HaDhn2) were accumulated differently, in tolerant compared with sensitive plants, during water deficit. In response to exogenous ABA in leaves of the R1 genotype, HaDhn1 and HaDhn2 transcripts were up-regulated and the steady-state level of HaElip1 transcripts was not modified (Ouvrard et al., 1996). HaDhn1- and HaDhn2-deduced proteins belong to the dehydrin family, and HaElip1 is a related homolog of early-light-induced protein (ELIP). Among the water-stress-induced proteins so far identified, dehydrins and the D-11 subgroup of late-embryogenesis-abundant (LEA) proteins (Dure et al., 1989) are frequently observed, and more than 65 plant dehydrin sequences are available (Close, 1997). Dehydrins are highly abundant in desiccation- tolerant seed embryos and accumulate during periods of water deficit in vegetative tissues. These proteins display particular structural features such as the highly conserved Lys-rich domain predicted to be involved in hydrophobic interaction leading to macromolecule stabilization (Close, 1996). Very little is known about dehydrin functions in plant. Studies have established correlations between drought adaptation and dehydrin accumulation in wheat and poplar (Labhilili et al., 1995; Pelah et al., 1997). Positive correlations were also reported for species tolerant to stresses that have a dehydrative component such as salt stress (Galvez et al., 1993; Moons et al., 1995) and freezing and cold stress (Arora and Wisniewski, 1994; Close, 1996; Artlip et al., 1997). Physiological observations associated with the varietal difference in tolerance have been reported (Moons et al., 1995; Pelah et al., 1997). In most of the published studies, gene expression was described as a function of time after the stress was applied, rather than as a function of parameters describing the plant’s water status. So, it is difficult to determine from these data precise relationships between plant physiological responses to drought and drought-induced gene expression.
5 Wheat yield improvement in the semiarid area Evidence in drought resistance breeding showed that a high yield potential is negatively
associated with certain drought adaptive traits in wheat (Blum, 1993). Such a negative association may put a limit on raising potential yield as means for improving actual yield under semiarid conditions. For a relatively determinate target stress environment and with stable genotype environment interaction, the probability of achieving progress is high. This approach will be possible only after we learn more about the physiology and genetics of wheat plant responses to water stress and their interactions. The difficulties encountered by molecular biologists in attempting to improve crop drought resistance are due to our ignorance in agronomy and crop physiology and not to lack of knowledge or technical expertise in molecular biology. Recent advances in crop management have enabled the production of winter wheat in most of the Canadian (Entz and Fowler, 1991). They comparatively studied the agronomic performance of dominant hard red winter and high-quality hard red spring wheat cultivars in semiarid and dry subhumid regions of Saskatchewan. Their results showed that in 15 trials, winter wheat (WW) over yielded spring wheat (SW) by an average of 36%; and in three trials, ’Norstar’ WW yielded 26% higher than the high-yielding semidwarf SW, ’RY 320.’ Protein yield was higher for WW in two of 15 trials and protein concentration was always higher for SW. Higher grain yield of WW was attributed mainly to the production of a higher kernel number per square meter (KNO). Crop development rate, aerial dry matter production, evapotranspiration (ET), and water use efficiency (WUE), were measured for Norstar WW and ’Katepwa’ SW in six trials grown between 1986 and 1988. The period between Zadoks growth stage (ZGS) 21 and 65 was 4 to 14 d longer for Norstar than for Katepwa. Average daily air temperature between ZGS 21 and
The WUE for dry matter production, grain yield and grain protein yield was consistently higher for Norstar. Long-term N fertilizer trials for dryland wheat are frequently confounded by large year-to-year variability in yields resulting from moisture stress fluctuations. To account for this variability, Korentajer and Berliner (1988) conducted a N fertilizer study in which the magnitude of moisture stress was monitored. Their experiment was carried out on a loamy fine sand soil, with wheat (cv. Betta), using a completely randomized block design with four replicates and five of N fertilizer levels: 0, 30, 60, 90, and 120 kg N ha-1. The seasonal moisture stress index, S, was estimated from a weighted product of ET/ET(p) ratios (actual to potential evapotranspiration) obtained for the different phenological wheat growing periods. The ET was estimated from soil moisture (monitored by means of a neutron moisture meter), whereas ET(p) was calculated from meteorological measurements using Penman’s equation. The response to N in both relatively dry and wet years was significant with mean yields of 3.18 and 1.7 ton ha-1, respectively. The data were statistically analyzed by means of a postulated multiple regression model with N and S levels as the explanatory variables. The model was validated using yield and meteorological data from several other 2-yr N response studies. A good correlation (R2 = 0.63, standard error of the estimate = 0.27 ton ha-1) was obtained between the predicted and the observed yields. Their results highlight the need for moisture stress measurements to be included in fertilizer trials conducted in areas of large seasonal rainfall variability. In the molecular physiology aspects, Loggini et al. (1999) analyzed antioxidative defenses, photosynthesis, and pigments (especially xanthophyll-cycle components) in two wheat (Triticum durum Desf.) cultivars, Adamello and Ofanto, during dehydration and rehydration. They wished to determine the difference in their sensitivities to drought and to elucidate the role of different protective mechanisms against oxidative stress. Drought caused a more pronounced inhibition in growth and photosynthetic rates of the more sensitive cv Adamello compared with the relatively tolerant cv Ofanto. During dehydration the glutathione content decreased in both wheat cultivars, but only cv Adamello showed a significant increase in glutathione reductase and hydrogen peroxide-glutathione peroxidase activities. The activation states of two sulfhydryl-containing chloroplast enzymes,
NADP+-dependent glyceraldehyde-3-phosphate dehydrogenase and fructose-1,6-bisphosphatase, were maintained at control levels during dehydration and rehydration in both cultivars. This indicates that the defense systems involved are efficient in the protection of sulfhydryl groups against oxidation. Drought did not cause significant effects on lipid peroxidation. Upon dehydration, a decline in chlorophyll a, lutein, neoxanthin, and -carotene contents, and an increase in the pool of de-epoxidized xanthophyll-cycle components (i.e. zeaxanthin and antheraxanthin), were evident only in cv Adamello. Accordingly, after exposure to drought, cv Adamello showed a larger reduction in the actual photosystem II photochemical efficiency and a higher increase in nonradiative energy dissipation than cv Ofanto. Although differences in zeaxanthin content were not sufficient to explain the difference in drought tolerance between the two cultivars, zeaxanthin formation may be relevant in avoiding irreversible damage to photosystem II in the more sensitive cultivar.
6 Conclusions It is clear that the greatest fear of global climate changes is drought. Even today, water is the most important factor influencing crop growth. In the world, 61% of the country receives a rainfall of less than 500mm annually, which is considered the minimum for successful dryland farming, but more highly populated, industrial and mining centers of the country. This is rapidly becoming less feasible, however, and greater attention should be paid to the management of demand and more efficient use of water. Undertaking dryland cropping in areas of the country where the long term annual rainfall is equal to or less than the minimum required to successfully sustain such activities will inevitably lead to drought, and this is more an indication of unwise farming rather than unusual weather. The agricultural industry often equates conservation programs with arable land reductions and increased production costs. Conservation production represents a opportunity to combine both increased agricultural productivity and resource conservation. Conservation production embraces the philosophies of profitable conservation farming by providing the opportunity for:
Improved control of soil erosion. More efficient crop moisture utilization. Higher crop productivity. Longer crop rotations no summer fallow. Reduced tillage. Improved water use efficiency. The domestication of wheat occurred in the semiarid region of southwestern Asia bordered on one side by the Tigris-Euphrates basin (ancient Mesopotamia) and on the other by the mountains of Iran, Turkey, Syria, and Jordan. This region is
Triticum monococcum dicoccoides
turgidum
T. sphaerococcum
aesttivum
2
2
processes underlying plant response to water deficit, at the molecular and whole-plant levels, has rapidly progressed. Knowledge of these processes is essential for a holistic understanding of crop resistance to water stress, which is needed to improve crop management and breeding techniques. Hundreds of genes that are induced under drought have been identified (Chaves et al., 2003). Due to crop responses to drought stress are complex, the functions of many other genes are still unknown. The new tools that operate at molecular, whole-plant and ecosystem levels are revolutionizing our understanding of plant response to drought, and our ability to monitor it. For example, Carbon isotope discrimination (△13C) is a measure of the 13C/12C ratio in plant material relative to the value the same ratio in the air on which plants feed. Farquhar (2002) showed that△ 13 C is positively related to the ratio of the intercellular CO2 concentration and the atmospheric CO2 concentration. Therefore △13C correlates with WUE. Consequently, △13C, due to its convenience and relatively cheap cost, has become a useful indicator of differences in WUE. Recently this method has been used for high WUE breeding in wheat (Condon et al., 2002). Other techniques such as genome-wide tools and thermal or fluorescence imaging may allow the genotype
105
Prunus persica Biology 33
Plant Molecular
Agronomy Journal 85 Critical
Reviews
in
Plant
Sciences 2, In
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Experimental agriculture 29
30
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42
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Puddling depth and intensity effects in rice-wheat system on water use and crop performance in a sandy loam soil S. S. Kukal Department of Soils, Punjab Agricultural University, Ludhiana-141 004, India.
Abstract A three year field experiment was conducted on a sandy loam soil to study the effect of puddling intensity and puddling depth on irrigation water use in rice (Oryza sativa) and the performance of rice and wheat (Triticum aestivum) crops. The treatments in main plots included (i) unpuddled plots, (ii) and (iii) medium puddling-2 passes of tractor-drawn cultivator followed by leveling with a wooden plank and (iv) and (v) intensive puddling-4 passes of tractor-drawn cultivator followed by leveling with a wooden plank, each at shallow (5-6 cm) and normal (10-12 cm) depths. Percolation losses decreased by 14-16% with increase in puddling intensity from medium to high, whereas irrigation water applied decreased by 10-25%. Intensive puddling intensity resulted in higher root mass density in 0-5 cm and 5-10 cm soil layers. Root mass density in shallow-puddled plots was 17% more in 0-5 cm soil layer than in normal-puddled plots. Puddling treatments had no effect on total dry matter and grain yield of Rice during all three years of study. Root mass density of Wheat in 0-15 cm soil layer increased from 301.9 ? g cm-3 in 1994-95 to 318.7 ? g cm-3 in 1996-97 whereas in 15-30 cm soil layer it decreased from 85.1 to 47.1 ? g cm-3. High puddling increased canopy temperature of wheat by 0.5-1.7oC and decreased xylem water potential by 4-7%. Total dry matter and grain yield of wheat was 19 and 8% more respectively in shallow-puddled plots than in normal-puddled plots during 1996-97. Key words: Puddling intensity; puddling depth; water use; rice-wheat cropping system; root mass density. E-mail:
[email protected]
1 Introduction Rice-wheat is the most popular cropping sequence of north-west India. The area under irrigated rice in Punjab State has increased from 0.29 million ha in 1965-66 to 2.2 million ha in 1997-98 due to an assured market and higher economic returns. The shift, mainly under coarse-textured soils, however, has resulted in increased demands on irrigation water as water requirements of low-land rice on coarse textured soils are very high (Aujla et al., 1984; Aggarwal et al., 1995). Puddling has been the most commonly used practice under transplanted rice culture, as apart from reducing percolation losses, it helps to control weeds and creates a soft medium for easy transplantation of rice seedlings (De Datta et al., 1979). The extent of reduction in the percolation losses depends on puddling intensity. High puddling intensity however, enhances the development of a hard pan and has detrimental effects on the growth and yield of succeeding wheat crops (Aggarwal et al., 1995). Apart from this, there has been a deterioration in soil physical conditions (Aggarwal et al., 1995; Kukal and Aggarwal, 2002) and resultant reductions in wheat yields following rice (Sur et al., 1981; Gill and
Aulakh, 1990; Aggarwal et al., 1995). This decrease in wheat yield may be due to the reduction in root growth and distribution under poor soil physical environment (Oussible et al., 1992; Hassan and Gregory, 1999; Ishaq et al., 2001). Several researchers (Lal, 1996; Flowers and Lal, 1998) have examined the effect of uniform soil surface compaction on crop root growth. Willatt (1986) observed that root length density in the upper 0.30 m of soil root depth decreased as the number of tractor passes increased from zero to six. Adverse effects of increased puddling intensity on plant root growth and yields have been recognized for many years (Etana and Hakansson, 1994; Jorajuria et al., 1997). Reduced root growth limits water uptake and consequently plants may experience water stress and thus lower crop yields. While deep tillage before sowing ameliorates the adverse effect of a compact layer on wheat growth, it is a difficult practice for most of the farmers due to lack of high-powered tractors and special implements like chisel ploughs. Puddling at shallow depth results in development of subsurface compaction at a shallower depth, which may be loosened during normal cultivation for wheat seedbed preparation (Kukal and Aggarwal, 2002). Thus shallow puddling may be a practical way of
2 reducing the water requirements of rice without having an adverse effect on yields of rice and the following wheat crop. The present study was planned with the objective of studying effects of puddling intensity and puddling depth on water use, growth and yield of rice and succeeding wheat crop.
2 Materials and methods A field experiment was initiated at Ludhiana (30? ?
-1 4
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3
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3 Results and discussion 3.1 Water use in rice
th
Table 1. Effect of puddling depth and puddling intensity on average percolation rate and irrigation water applied to rice Year
Puddling intensity Medium Percolation rate (mm day )* 1994 13.8 1995 13.4 1996 13.5 Mean 13.2 Irrigated water (mm)** 1994 499 1995 538 1996 641 Mean 559
Intensive
LSD
Puddling depth Shallow
Normal
LSD
11.6 11.5 11.6 11.9
0.09 0.04 0.01
12.1 12.8 12.8 12.6
13.4 12.2 12.2 12.6
NS NS NS
375 489 497 454
42 48 40
428 504 584 505
447 472 554 491
NS NS NS
Puddling depth x puddling intensity interaction was not significant (NS)
Medium puddling resulted in a decrease of percolation losses by 120-130% from that in unpuddled plots over different years (Table 1). Increasing puddling intensity from medium to intensive did not decrease the percolation rate of water significantly during all the years of study. Puddling of soil results in disruption of soil aggregates and creation of a soil-water suspension. The differential settling of soil particles results in sealing of the puddled surface with clay particles, thereby reducing the percolation losses of water. Aggarwal et al (1995) observed the percolation rate of water to be 4, 12 and 10 mm day-1 under low, medium and high puddling intensity, respectively. The reduction in percolation losses lowered the irrigation water requirement of rice (Table 1). Mean irrigation water applied to rice decreased by 25% in 1994, 10% in 1995 and 22% in 1996 when puddling intensity increased from medium to intensive. Puddling depth, however, had no significant effect on percolation losses and amount of irrigation water applied. Interactive effects of puddling depth and puddling intensity on percolation rate and irrigation water applied were not significant. 3.2 Rice root growth Root mass density (RMD) at the reproductive stage of rice significantly increased with puddling intensity in 0-5 and 5-10 cm soil layers (Table 2). It was higher by 5% in 0-5 cm and 15% in 5-10 cm soil layers with intensive puddling compared to that with medium puddling intensity. In all other layers, the difference was non-significant. High puddling has been reported to increase root proliferation due to better softness of puddling (Singh et al 1995). Puddling depth had significant effect on root mass density (RMD) of 0-20 cm soil layer. In 0-5 cm soil layer, RMD of rice was 17% higher in shallow-puddled soils than in normal-
puddled soils. It could be due to the shallow depth of puddling (5-6 cm) in shallow-puddled plots, which resulted in concentration of higher root mass in this surface layer. The root mass density was lower in 510 and 10-15 cm soil layers of shallow-puddled plots. It could be again due to more depth of puddled layer in normal-puddled plots, which resulted in penetration of roots into lower layers. However, in 15-20 cm soil layers, the RMD was higher in shallow-puddled soils. This may be due to the presence of a compact layer in normal-puddled soils, which hindered the penetration of roots in this layer. No significant differences were observed in 20-25 and 25-30 cm soil layers. Kundu et al (1996) observed that depth of tillage treatments significantly influenced root mass distribution of rice in different soil layers. Increasing the puddling depth increases the depth of soil disturbance and creates deeper soft medium in normal depth of puddling than in the shallow puddling depth. Thanagaraj et al (1990) observed decreased root growth with increasing soil mechanical impedance. 3.3 Rice growth and yield Puddling treatments did not affect total dry matter and grain yield of rice significantly (Table 3). The yields were low during 1994, owing to the attack of stem borer. The average (1994-96) rice grain yield under medium and intensive puddling was 5.96 and 6.09 t ha-1, respectively. The depth of puddling had no effect on the yield of rice as the water and nutrient availability to rice were not limiting. Moreover, rice has a shallow root system with about 90% of the total root length of transplanted rice being in the top 20 cm of soil (Sharma et al., 1987). The variation in root mass density in this zone was not reflected in rice growth and yield due to sufficiency of nutrients and water in the surface layers of shallow puddle. Similar results have been reported by Aggarwal et al (1995).
Table 2. Effect of puddling depth and puddling intensity on root mass density (kg m )of rice at reproductive stage during third year of study* Soil depth(cm) Shallow 2.21 1.02 0.22 0.19 0.09 0.04
0-5 5-10 10-15 15-20 20-25 25-30
Puddling depth Normal 1.83 1.23 0.73 0.03 0.05 0.05
Puddling intensity Medium 1.98 1.05 0.49 0.23 0.08 0.07
LSD 0.04 0.03 0.14 0.01 NS NS
Intensive 2.07 1.21 0.46 0.29 0.08 0.05
LSD 0.03 0.04 NS NS NS NS
Puddling depth x puddling intensity interaction was not significant (NS)
Table 3. Total dry matter and grain yield of rice in relation to puddling depth and puddling intensity Year
Puddling depth Shallow
Normal
1994
11.6
11.0
1995
22.9
23.1
1996
17.2
18.8
Mean
17.2
17.6
Puddling intensity
LSD Medium Total dry matter yield (Mg ha ) NS 11.8
Intensive
LSD
10.8
NS
NS
22.8
23.3
NS
NS
17.3
18.7
NS
17.3
17.6
4.41 6.98 6.21 5.87
4.55 7.17 6.81 6.18
Grain yield (Mg ha ) 1994 1995 1996 Mean
4.37 7.06 6.44 5.96
5.59 7.09 6.60 6.09
NS NS NS
3.4 Wheat root growth Root mass, leaf yellowing and plant N content of wheat after first irrigation (30 days after sowing) in relation to puddling treatments are presented in table 4. Root mass of wheat in the 0-20 cm soil layer was not significantly different for the medium and high puddling intensities during all the three years of study. The yellowing of leaves with symptoms of N deficiency were observed in wheat crop during 199495 due to rains just 3 days after the first irrigation. However, there was no significant difference between treatments. However, during 1996-97, the number of yellow leaves was 13.4% more in soils with intensive puddling intensity compared to that with medium puddling intensity. The N content was significantly less in plants grown on intensively puddled soils than that in medium puddled soils. High puddling thus proved detrimental during the third year of wheat cropping. Puddling depth significantly affected root mass of the 0-20 cm soil layer during 1995-96 and 1996-97. The increase was 36% in 1995-96 and 121% in 199697 in shallow-puddled plots compared with normalpuddled plots. It could be due to high bulk density of 14-20 cm soil layer in normal-puddled soils (Kukal and Aggarwal, 2002). Soil penetration resistance of more than the critical value of 3 MPa adversely affects the wheat root growth (Coelho et al., 2000).
NS NS NS
Leaf yellowing was 108% more in normal-puddled soils than in shallow-puddled soils. This in turn resulted in a higher N content of plants in shallowpuddled soils than in soils puddled to normal depth. Ishaq et al (2001) reported a reduction of 12-35% in N uptake by wheat due to subsoil compaction. At the reproductive stage during 1996-97, root mass density of wheat was significantly different amongst the various puddling treatments (Table 5). Puddling resulted in higher RMD of wheat in the 0-15 cm soil layer than in unpuddled plots, whereas in lower layers the RMD was higher in unpuddled plots. Thus with puddling more roots were concentrated in the upper (0-15 cm) soil layer. This concentration increased with increase in puddling intensity from medium to intensive. However, the reverse was true in lower layers. The RMD of 0-15 cm soil layer was 2.5% more in intensive-puddled soils than in mediumpuddled soils whereas in 15-30, 30-60 and 60-90 cm soil layers, the RMD was significantly higher by 16.8, 23.1 and 48.6% respectively in medium-puddeled plots than in intensive-puddled plots. It could be due to more subsurface compaction with intensive puddling intensity than with medium puddling intensity (Kukal and Aggarwal, 2002). A similar trend was observed with puddling depth treatments. RMD in 0-15 cm soil layer was 6.7% more in normalpuddled plots than in shallow-puddled plots. However,
5 soils. The high bulk density layer at 14-20 cm soil depth (Kukal and Aggarwal, 2002) in normal puddled soils might have restricted the downward movement of roots in lower layers, thereby concentrating these in the 0-15 cm soil layer. Adverse effects of subsoil compaction on plant root growth have been reported (Unger and Kaspar 1994; Jorajuria et al., 1997).
in lower layers the opposite was the case. The RMD was 68.2, 50.5, 11.1 and 29.1% less in 15-30, 30-60, 60-90 and 90-120 cm soil layers respectively, in normal-puddled plots compared to that in shallowpuddled plots. This was due to higher mechanical impedance in normal-puddled plots than in shallowpuddled plots associated with a compact zone at 14-20 cm soil depth (Kukal and Aggarwal, 2002). Ishaq et al (2001) reported a decrease in root length density of wheat below 0-15 cm depth measured at flowering stage due to subsoil compaction and found that it was significantly and negatively correlated with soil bulk density. Average RMD in the 0-15 cm soil layer increased with time (Table 6). It was 304.3 ? g cm-3 in 1994-95, 316.7 ? g cm-3 in 1995-96 and 318.8 ? g cm-3 in 199697. But in the 15-30 cm soil layer, RMD decreased by 24% during 1995-96 and 45% during 1996-97 from that in 1994-95. In the 0-15 cm soil layer, there was no significant difference in RMD due to puddling depth during 1994-95, but during 1995-96 and 199697, it was 10 and 15% more in normal puddled soils than in shallow puddled soils. However, RMD of the 15-30 cm soil layer decreased by 38.4 and 68.2% during 1995-96 and 1996-97, respectively in normalpuddled soils compared to that in shallow-puddled
3.5 Wheat plant water status Canopy temperature and xylem water potential of wheat at different growth stages were not affected by puddling treatments in rice during 1994-95 and 199596. However, during 1996-97, intensive-puddled plots had significantly higher canopy temperatures compared to medium-puddled plots (Table 7). The
Table 4. Extent of leaf yellowing, N plant content and root mass (0-20cm soil layer) of wheat at 30 DAS as affected by puddling treatments in preceding rice Year
Puddling depth Shallow
1994-95
13.0
1995-96
-
1996-97
17.8
1994-95 1995-96 1996-97
3.11 3.17 3.12
1994-95 1995-96 1996-97
0.31 0.34 0.31
Normal 13.0
Puddling intensity
LSD Medium Leaf yellowing (No.m-row ) NS 13.0
High
LSD
13.0
NS
-
-
-
-
-
37.0
1.4
25.4
28.8
1.4
3.12 3.15 3.08
3.11 3.14 3.04
NS NS 0.01
0.30 0.32 0.23
0.29 0.29 0.24
NS NS NS
Plant N content(%)
Soil depth(cm)
3.11 3.12 2.99 0.28 0.25 0.14
NS NS 0.01 Root mass (g) NS 0.03 0.04
Puddling depth
0-5 15-30 30-60
Shallow 308.0 71.4 31.3
60-90
14.4
90-120
11.0
Normal 328.7 22.7 15.5
Puddling intensity
LSD 2.2 3.1 3.0
Medium 314.1 50.7 23.9
High 322.6 43.4 19.5
LSD 2.2 3.0 2.9
12.8
1.4
16.2
10.9
1.3
7.8
2.3
10.5
8.2
NS
6
Table 6. Root mass density of wheat in 0-15 and 15-30cm soil layer in relation to puddling treatments in preceding rice crop Year
Puddling depth
Shallow 0-
Normal
Mean
Table 7. Canopy temperature and xylem water potential of wheat at different growth stages as affected by puddling treatments in preceding rice during third year of study
3.6 Wheat growth and yield Grain yield of wheat was not significantly affected by puddling intensity (Table 8). However, puddling depth significantly affected grain yield. In 1996-97, plots puddled at normal depth yielded 8% less than those puddled at shallow depth. This reduction in yield could be attributed to subsurface compaction (Oussible et al., 1992) in plots puddled to normal depth. Average grain yield (irrespective of puddling treatments) decreased over different years (Table 9), but the decrease was significant during the third year of study (1996-97). The grain yield during 1996-97 was 5% less than that during 1995-96. Puddling intensity did not interact with time to affect grain yield. However, puddling depth interacted
significantly with time to affect grain yield. The difference in grain yield under shallow and normal puddling depths was 1% in 1994-95 whereas it increased to 8% in 1996-97. Xylem water potential of wheat at 105 and 120 DAS during 1996-97 was significantly affected by puddling intensity and puddling depth (Table 7). High puddling decreased xylem water potential by 7 and 4% from that with medium puddling at 105 and 120 DAS respectively. Shallow-puddled plots had 17 and 15% more xylem water potential at 105 and 120 DAS respectively. The differences could again be attributed to restricted root growth in normal-puddled plots compared to that in shallow-puddled plots.1111111111111111111111111
Table 8. Interactive effect of puddling intensity and puddling depth in preceding rice on grain yield of wheat (Mg ha-1) over different years
4. Conclusions Increasing puddling intensity from medium to intensive decreased percolation rate by 14-16% and applied irrigation water by 10-25%, whereas puddling depth did not affect these parameters. Root mass densilty of rice in 0-5 and 5-10 cm soil layers increased with increase in puddling intensity. It was significantly affected by puddling depth. Rice yields were not affected by puddling treatments during all the three years of study. Increased puddling intensity proved to be detrimental to the wheat crop during the third year of study. Intensive puddling intensity increased RMD of wheat in the 0-15 cm soil layer whereas it decreased RMD in lower layers. RMD in the 0-15 cm soil layer of normal-puddled plots was more than that in shallow-puddled plots, whereas in lower layers it was less by 11-68%. Intensive puddling intensity resulted in higher values of canopy temperature and xylem water potential. Dry matter and grain yield of wheat were 19 and 8% more in shallow-puddled plots, respectively, compared to those in normal-puddled plots. This shows that puddling, if done at shallow depth, creates a better environment for crop growth especially wheat than when it is done at normal depth, without affecting percolation losses and water requirements during rice cropping.
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18
16
60
41
60
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References Aggarwal, G.C., Sidhu, A.S., Sekhon, N.K., Sandhu, K.S., Sur, H.S., 1995. Puddling and N management effects on crop response in a ricewheat cropping system. Soil Till. Res. 36, 129-139. Aujla, T.S., Singh, B., Khera, K.L, Sandhu, B.S., 1984. Response of rice to differential irrigations at growth stages on a sandy loam soil in Punjab. Indian J. Ecol. 11, 71-76. Barraclough, P.B., Weir, A.H., 1988. Effects of a compacted subsoil layer on root and shoot growth, water use and nutrient uptake of winter wheat. J. Agric. Sci. Camb. 110, 207-216. Coelho, M.B., Mateos, L, Villalobos, F.J., 2000. Influence of a compacted loam subsoil layer on growth and yield of irrigated cotton in Southern Spain. Soil Till. Res. 57, 129-142. DeDatta, S.K., Morris, R.A., Barker, R., 1979. Land preparation and crop establishment for rainfed lowland rice.
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7
Water use efficiency of Oilseed Rape (Brassica Campestris) under even or patchy water supply Ling Wang 1,3, Hans de Kroon2, Toine Smits3 1
College of Water Resources and Environment, Hohai Uniiversity, Nanjing, 210098,China
2
Faculty of Ecology, University of Nijmegen, The Netherlands
3
Department of Environmental Science, University of Nijmegen, The Netherlands
Abstract Investigations were conducted into optimal water supply regimes, which encourage full use of the water provided. These were undertaken in a greenhouse experiment at the University of Nijmegen. The aim was to improve understanding of how root foraging characteristics respond to different water application patterns. Measurements were made for Oil Seed Rape (Brassica campestris), which is already widely cultivated in China. Four water supply patterns were implemented, namely fixed patch (T1), alternate patch (T2), or even water supply with same amount of water. Alternate wetting produced the highest WUE, though there were only small differences between values for T1, T2 and T3. Key words: Water Use Efficiency; Root foraging; partial soil wetting; drip irrigation; Brassica campestris E-mail:
[email protected]
1 Introduction Irrigated agriculture is facing competition for low-cost, high-quality water (Howell 2001). WUE is a simple concept to link water use to yield. Research is urgently needed towards complete understanding of the underlying mechanisms to bring higher WUE and provide higher yield to match the requirements of the growing population. Research on how to improve WUE through plant physiological approaches will improve our understanding of how crop response precisely to water application and will offer the opportunity to drastically increase WUE. Under natural conditions, natural resources are heterogeneously distributed both in space and time. Within a modular pattern of production, development of plants can be highly variability. Due to this highly flexible morphological plasticity, plants can alter their features to effectively respond to varied environment and can reach resource-rich patches to obtain necessary resources (Hutchings et al. 1994). Such a selective foraging-acquiring structure is an adaptation to varied environmental factors. This foraging behavior guarantees that plants obtain resources in a non-random way from micro-sites where enough essential resources located. It enhances the probability and efficiency of obtaining resources from favorable resources-rich patches and has significant practical implications. A better understanding is required of
selective root growth and consequent responses to localized water pools, to prompt optimal use of limited water resources. In recently years, plant physiology research has provided a large amount of evidence about high nutrient uptake efficiency when nutrients were applied unevenly. So now interests has been aroused over how a root foraging system will behave under the heterogeneous water supply pattern created by drip irrigation system? Will the heterogeneity of water environment bring high biomass production or crop production? Hopefully, complete knowledge of root system response to partial soil wetting created by a drip irrigation system will assist scientific farm management. A greenhouse experiment, at the University of Nijmegen, was conducted to explore whether or not an optimal pattern could be identified for making available amounts of water. It should improve our understanding of how root foraging characteristics respond to different water applying patterns. Oilseed rape (Brassica campestris) is the experimental crop species in the current study. To identify an optimal supply approach, we hypothesized that supplying water in a concentrated way would create more biomass production than spraying water in a uniform way. The following objectives are explored to check the possibility of defining an optimal water supply pattern for a fixed amount of water. Does applying water in a patchy way indeed bring about high
1
Figure 1. Fixed (T1) and alternate (T2)
patchy watering treatments
biomass production or higher WUE? What is the resulting root foraging behavior under different water supply pattern? Leaf extension is a sensitive indicator of response to water deficit (Sadras, et al. 1996). But how is leaf development and root morphology affected under different irrigation regimes and what are the consequences for biomass production?
2 Materials and methods Three water supply treatments were established namely fixed patchy drip irrigation (T1), alternate watered patchy drip irrigation (T2), and a uniform water supply pattern (T3) for pot-grown crops. Table 1 is a summary of the treatments, where T4 is a control having no water stress. Figure 1 illustrates T1 and T2. Table 1. Water supply treatments Treatment
Description
T1
fixed drip irrigation
T2
alternate drip irrigation
T3
evenly water supply
Control
well-watered
applied every two days to the three treatments, while 2 or 4-fold amounts of water were provided to the control to ensure that it remained well-watered, while avoiding drainage. Amounts of water were changed according to the different stages of crop growth while keeping in mind that drainage from the fixed drip irrigation treatment should avoided. A syringe was used to apply water uniformly to treatment T3. Four 600W high-pressure sodium lamps provided extra energy to the plants, from 6:00 ~ 22:00. The average humidity was around 65%, with temperature in the range 18 to 25?C, during the course of the experiment. Weeds were removed by hand during the course of the experiment. To identify the actual size of the enriched water patch, some extra pots without crops were also watered to track the wetted soil volume. Water supply during the course of the experiment was carefully recorded for the three treatments namely fixed patch water supply, alternate patch water supply and uniform water supply treatment, and for the control. Records were also maintained of initial soil water content. Crop development was measured in terms of leaf number, with leaf length and width of the 3rd, 6th, 9th true leaves being recorded weekly. At 63 days after sowing, root biomass was measured for the 4 quadrants of each treatment. For treatment 1, 2 cores were taken from quadrant 1 corresponding to the emitter placement and from quadrant 3, opposite to quadrant 1. Soil water content was also determined for the 2 cores. In addition, records were made of shoot biomass and leaf water content of the 9th leaf, being the latest fully expanded leaf of the control. The final soil water contents were also measured. Biomass were put into an oven and dried for 48 hours, keeping the temperature at 70oC.
3 Results and discussion Seeds were sown on 19th September, 2002 and 15 days after sowing, similar seedlings were transplanted into pots at the 2 true leaves stage. Ten seedlings were harvested to record the initial growth information. For each treatment 20 replicates were planted in pots, with both diameter and depth being 18 cm. The pots were filled with air-dried soil combination of potting soil and clay soil sieved with 4 mm filter and packed to a bulk density of 1.1gcm-1. The soil surface was covered with black plastic beads to prevent evaporation. Plants were placed in a completely randomized fashion. Time Domain Reflectometry (TDR) was used to monitor change of soil water content of the four quadrants of each of the three treatments, to confirm the patchy or uniform soil water distribution in pots during the drying period after water supply. The same amounts of water were
3.1 Water supply and soil water content Cumulative water supply for each of the three treatments is shown in Figure 2. TDR values for quadrant 1 of the three treatments (T1, T2 and T3) are presented in Figure 3. 3.2 Leaf growth Figure 4 shows the leaf development of the four treatments. At the beginning of the experiment, a water patch or water deficit had little influence on leaf number. As the experiment progressed and water deficit became obvious, then the control had about 2 more leaves than other treatments. 3.3 Total biomass and root biomass for different quadrants of pots
Total biomass data were analyzed using analysis of variance (ANOVA) in STATISTICA. Data was transformed by taking natural logarithms before
2
performing the analysis. One-way ANOVA analysis then carried out on the transformed data and Figure 5 shows the results. From this, both fixed and alternate drip supplies are seen to yield more biomass than the even water supply pattern. Hence the two localized supplies had higher levels of WUE. While the control yielded more biomass, by referring to Figure 2 it can be seen that the control used an almost three-fold amount of water so the WUE is not high compared to the treatments.
Figure 4. Leaf number Table 2 Biomass and water use efficiency data Total root biomass Treatment WUE (g/m3) (g) T1
1.532
4.5
T2
1.539
4.6
T3
1.297
4.1
Control
3.177
2.9
Figure 2. Water supply for treatments and control
c
b
b a
Figure 3. TDR measurement of the three deficit water supply treatments
It can be concluded that biomass was affected by soil water distribution patterns and total water supply. Table 2 presents biomass amounts and WUE values compared to the control. WUEs were calculated using the ratio of total biomass to water supply during the course of experiment. Quadrants 2 and 4 were assumed to have the same biomass, then mean root biomass was determined and results displayed in Figure 6. For the watered quadrant of the fixed drip water supply, the degree of root proliferation was similar to that
Figure 5. Water supply pattern effects on total biomass (P ?r 0.8. WUEAmax/gs increased by 50% with soil drying to FTSW 0.7 ?l ?l
?l
Amax
Key words: E-mail:
1 Introduction Chenopodium quinoa
1
Increasing soil moisture deficit may be accompanied by relative changes in ? r and ? l, xylem nitrate concentration, and xylem pH (Bahrun et al., 2002a). The reduction in the delivery of nitrate to shoots can regulate leaf processes independently from a variation in plant water (Dodd et al., 2002; Shaner and Boyer, 1976). When nitrate supply is limiting, regardless of soil water availability, stomata close and leaves grow more slowly, whereas root growth is maintained, often characterized by greater lateral root proliferation (Wilkinson and Davies, 2002). These symptoms of N deficiency are also symptoms of drought stress, so that the soil drying response may at least in part be a response to a limitation in N supply. One explanation for this is that when N is limiting there is a decrease in the supply of amino acids and structural proteins necessary for leaf growth. However, there is now evidence that a response to N deprivation is governed instead by fast root-shoot chemical signals (Wilkinson and Davies, 2002). The objective of this study was to investigate the sensitivity of gs and Amax of quinoa to progressive soil drying and its implication in altering water use efficiency. Additional characteristics affected by drought in other species were also studied, such as ? r and ? l, pH and conductivity of xylem sap, leaf and plant growth, nitrogen and carbon content of leaves, and dry matter accumulation.
the bud formation period (developmental stage 3-
n
f
2.3 Measurement of leaf water status, leaf expansion rate and stomatal conductance (gs)
2 Materials and methods
Amax
s
2.1 Plant material and growing conditions A pot experiment was conducted at the experimental station of the Royal Veterinary and Agricultural University (KVL), Taastrup, Denmark in 2002. Quinoa (Chenopodium quinoa Willd.), cv. INIA-Illpa from Puno, Peru (3825 masl, 16oS, 70oW) was grown in pots (15-cm diameter by 50-cm tall). The pots contained 1.0 kg cultural substrate (GB-Pindstrup Substrates No.1, pH = 6.0) and were housed in a controlled environment greenhouse [day/night air temperature 20/14 ? 2?C; 60% relative humidity; 12 h photoperiod at 600 ? mol m-2 s-1 PAR supplied by metal-halide lamps]. Four seeds per pot were sown on 28 June, 2002. When the first two leaves had emerged, thinning was carried out to one plant per pot. Pots were randomly arranged in the greenhouse.
2
1
1
2 1
2
1
?l
2.2 Water treatments Initially, the plants were irrigated daily with nutrient solution (Pioneer NPK Macro 14-3-23 + Mg combined with Pioneer Micro; pH = 5.5; EC = 1.3) to maintain full water holding capacity (WHC). Later, drought stress was imposed by withholding water and nutrients from pots during two alternative treatments. The first was during
??
2
?
?
2
equilibrium was reached before the final reading was taken (2 h equilibrium time). Leaf turgor (? p) was calculated as the difference between ? l and osmotic potential ? p = ? ? - ? l. In addition, number of leaves, plant height, stem diameter, fresh and dry weight (leaf, stem, inflorescence) were also measured.
A
Ci r2
2.4 Collection of xylem sap Xylem sap was collected by pressurizing the potted plant in a Scholander pressure chamber. The entire pot was sealed into the pressure chamber and the shoot was de-topped at 15-20 cm from the stem base. With the stem stump protruding outside the chamber, pressure was applied. The pressure of the chamber was increased gradually until it equalled the ? l of the plant. The cut surface was cleaned with pure water and dried with blotting paper. A piece of silicon tube was then placed on the stump so that the epidermis was not damaged and no leaking occurred. The top of the silicon tube was connected to the capillary top of an Eppendorf glass pipette. A small diameter silicon tube connected the capillary top with an Eppendorfvial wrapped in aluminum foil. A 0.5-1.0 ml of sample of the sap was collected over 5-10 min. in well-watered and 20-30 min. in drought-stressed ? plants. The sap was immediately stored at
3 Results 3.1 Soil water status
3.2 Gas exchange
2.5 Measurement of xylem pH and nitrate
-2
2
2.6 Data analysis and statistics max
Ci ?
=
A?
? Ci
Amax
-1
-2
-1
2
-1
gs Amax s
s
Amax ? Ci
A Ci ? l, ? r
3
-1
gs
1.2 1.0
b
1.2
0.6
FTSW
1.0
0.8 FTSW
1.4
a
Droughted
0.4
Control
0.2
0.8 0.6 0.4 0.2
0.0 0
5
10
15
0.0
20
0
Days after drought
5
10
15
20
Days after drought
Figure 1. Water use, measured as FTSW, during drying at a) bud formation and b) anthesis 3
3
b
2
Stomatal cond., mol m s
Stomatal cond., mol m s
a
D C
1
2
1
0
0 0
5
10
15
0
20
5
10
15
20
Days after drought
Days after drought
Figure 2. Stomatal conductance (gs) at a) bud formation and b) anthesis 30
a
25 20 15
Photosynthesis, mol m s
Photosynthesis, mol m s
30
D
10
C
5 0
b
25 20 15 10 5 0
0
5
10
15
0
20
5
10 Days after drought
Days after drought
Figure 3. Photosynthesis (Amax) at a) bud formation, and b) anthesis
4
15
20
0
Leaf and root water potential
0
5
10
15
0
20
Leaf and root water potential
0
a
-1
-2
-3
LWP
5
10
15
20
b
-1
-2
-3
RWP
-4
-4
Days after drought
Days after drought
Figure 4. Development of leaf (? l) and root water (? r) potential at a) bud formation, and b) anthesis 1500
1500
b
1000
LER, mm d plant
LER, mm d pl.
a
Droughted Control
500
0
1000
500
0
0
5
10
15
20
0
5
10
15
20
Days after drought
Days after drought
Figure 5. Leaf expansion rate (LER) at a) bud formation, and b) anthesis
3.3 Leaf and root water potential The ? r of drought-stressed plants at bud formation decreased after nine days (Figure 4a), however, ? l was maintained above -1 MPa. This was not the case for plants at anthesis, where ? l decreased below r
1000
y = 376.75Ln(x) + 735.57 R = 0.7917
b
Leaf area, cm
800
3.4 Xylem sap pH and conductivity
600
D C
400
y = 197.67Ln(x) + 616.55 R = 0.5464
200
-1
0
0.0
0.5
1.0
1.5
2.0
Stem dryweight, g
Figure 6. Leaf area as a function of stem dry weight
3.5 Leaf expansion rate
2 2
-1
-1
5
-1
-1
weight, the fully watered plants developed more leaf area for a certain level of stem weight than the drought-stressed plants (Figure 6).
3.7 Relationships between the relative values of biophysical parameters and FTSW or ? r 3.7.1 Soil water status At both bud formation and anthesis, whole plant transpiration was maintained until a threshold value of FTSW 0.6 was reached (Figure 7a,b). 3.7.2 Gas exchange We used linear-plateau functions to compare gs and Amax of droughtstressed plants relative to well-watered plants as a function of FTSW (Equation 3) (Figure 8). When FTSW decreased beyond the threshold, the values of relative gs and Amax declined linearly in plants at bud formation. In plants at anthesis, gs decreased more quickly, whereas Amax was maintained.
3.6 N and C The N content of leaves remained at 5-6%, with no difference between drought-stressed and control plants, or between the two phenological phases. In contrast, the C content of leaves was higher in the well-watered treatment (38%) compared to than drought-stressed treatment (34%) for plants at bud formation. At anthesis, the C content of leaves was 38-40% for both treatments. In the drought-stressed treatment, the C/N ratio was about 7 for plants at bud formation and about 6 for plants at anthesis. 1.4
1.4 a Relative transpiration
Relative transpiration
1.2 1.0 0.8 0.6 0.4 0.2
b
1.2 1.0 0.8 0.6 0.4 0.2
0.0
0.0 1.4
1.2 1.0
0.8
0.6
0.4 0.2
0.0
1.4 1.2 1.0 0.8 0.6 0.4 0.2
FTSW
0.0
FTSW
Figure 7. Relationship between relative values of transpiration and FTSW at a) bud formation and b) anthesis
Relative Amax in plants at bud formation decreased only slightly until 0.8, with a decrease in relative ? r, much less than gs. The curvilinear function between relative Amax and relative gs indicated an efficient Amax (Figure 9a,b), which was confirmed by the increase in relative WUE with soil drying (Figure 10a,b). 3.7.3 Leaf and root water potentia From the onset of drought, relative ? r decreased linearly to 0 for plants at both phenological stages. The ? l for plants at bud formation was maintained above 0.8 (Figure 11a), but for plants at anthesis, ? l decreased with soil drying (Figure 11b). 3.7.4 LER For plants at bud formation, LER decreased rapidly after the imposition of drought until FTSW reached 0.8, then LER became nearly constant (Figure 12a). For plants at anthesis, the effect of drought on LER became progressively more serious with increasing drought (Figure 12b). Leaf growth, indicated by the relative values of LER and leaf area (drought-stressed relative to
well-watered plants as a function of FTSW), showed immediate sensitivity to drought, stabilizing when reaching FTSW=0.7 (data not shown). Daily LER, measured on single leaves, decreased just after the onset of drought relative leaf expansion rate decreased. LER reached a plateau from FTSW 0.7 to 0.3 LER, and declined thereafter until the end of sampling. The decrease in leaf growth was similar between leaf length and width. Relative leaf area decreased linearly with relative ? r. Relative LER/d decreased to a stable, relatively high level. Relative height and total dry weight also decreased with ? r. 3.7.5 N and C Relative N and C of leaves decreased slightly with increased drought, but the C/N ratio remained constant. 3.7.6 Dry matter content DM, on the other hand, increased linearly above the threshold value, for plants at both bud formation and anthesis. Individual plant parts also changed similarly. Height was maintained until FTSW 0.48.
6
1.2
1.2 Relative photosynthesis
1.4
1.0 0.8 0.6 0.4
0.8 0.6 0.4 0.2
0.0
0.0
1.2
1.2
1.0 0.8 0.6 0.4
FTSW
1.0 0.8 0.6 0.4
0.2
0.2
0.0
0.0
6
6
5
5 4
PWUE
PWUE
1.0
0.2
Relative stomatal cond.
Relative photosynthesis Relative conductance
1.4
3 2
4 3 2
1
1
0
0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.4
1.2
1.0
FTSW
a) bud formation
0.8
0.6
0.4
0.2
0.0
FTSW
b) anthesis
Figure 8. Relative photosynthesis (Amax), stomatal conductance (gs) and photosynthetic WUE as influenced by soil drying at a) bud formation b) anthesis 1.2
y = 0.5314Ln(x) + 0.9651 R = 0.7871
1.0
Relative photosynthesis
Relative photosynthesis
1.2
a
0.8 0.6 0.4 0.2 0.0
b
1.0 0.8 0.6 0.4
y = 0.3012Ln(x) + 1.0348 R = 0.7997
0.2 0.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
Relative conductance
1.0
0.8
0.6
0.4
0.2
0.0
Relative conductance
Figure 9. Relationship between relative photosynthesis (Amax) and relative stomatal conductance (gs) at a) bud formation and b) anthesis
7
15
15
b
Relative WUE
Relative WUE
a 10
5
0
10
5
0 1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
0.8
FTSW
0.6
0.4
0.2
0.0
FTSW
Figure 10. Relative WUE under drought at a) bud formation and b) anthesis 1.4
1.4
Relative LER
1.0 Relative LER
1.2
a
1.2
0.8 0.6 0.4
b
1.0 0.8 0.6 0.4 0.2
0.2 0.0
0.0
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
FTSW
FTSW
Figure 11. ? l and ? r under drought at a) bud formation and b) anthesis 1.2
1.2
b
a
0.8 0.6 0.4
1.0
Relative potential
Relative potential
1.0
y = 0.2191x + 0.8491 R = 0.1074
y = 1.0982x - 0.0721 R = 0.929
LWP
0.2
y = 0.5516x + 0.3587 R = 0.9238
0.8 0.6 0.4
y = 0.8053x - 0.037 R = 0.7921
0.2
LWP
RWP
RWP
0.0
0.0 1.2
1.0
0.8
0.6
0.4
0.2
1.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
FTSW
FTSW
Figure 12 Relative LER under drought at a) bud formation, and b) anthesis
4
Brassica Lupinus
Discussion napus angustifolius
4.1 Stomatal closure Previous researchers found that the stomatal response of quinoa was insensitive to soil drying, as stomatal closure did not occur before ? l was below
Triticum aestivum
?
8
gs Amax
at 1, until the FTSW dropped to 0.33 ? 0.061. The relationship between relative gs and relative Amax was represented by a logarithmic function (r2 = 0.79), which resulted in a WUEAmax/gs of 1 when FTSW > 0.8. WUEAmax/gs increased by 50% at FTSW 0.7 gs Amax
gs gs Amax ? r Amax
gs gs 4.2 Xylem pH and conductivity
Amax +
gs Amax gs
r
gs gs Glycine max Helianthus annuus
+
Zea mays Cicer arietinum
gs
Amax 4.3 Water potential ?r
?l
Hordeum vulgare gs
?r
?l ?l ?l
?l ?l
?l
?l
?l ?l ?l
9
?r
was shown that the N content in quinoa decreased from 5 to 3% under drought, because of limited uptake of N from the drying soil (Jensen et al., 2000). This corresponds to the rapid decline in LER following withdrawal of nitrate from the roots (McDonald and Davies, 1996). The difference may be due to difference in the soil material used in our experiment compared to the field soil of the lysimeter of Jensen et al. (2000).
4.4 Leaf expansion LER of well-watered plants measured for quinoa was higher (up to 500 and 1500 cm2 d-1 plant-1 at bud formation and anthesis, respectively), than for soybeans, grown under the same conditions with respect to soil type and pot size (max 270 cm2 d-1 plant-1) (Liu et al., 2003). LER began to decrease just after the onset of drought, which was before the threshold value for gs, indicating a significant effect of drought on leaf expansion. This is similar to observations in other crops where leaf expansion is more sensitive to soil water deficits than gs (Boyer, 1970; Saab and Sharp, 1989; Sadras and Milroy, 1996). The soil-water threshold for leaf area expansion has shown to be 0.29 for soybean (Liu et al., 2003), chickpea 0.48 (Soltani et al., 2000), and field pea 0.40 (Lecoeur and Sinclair, 1996). For quinoa, the threshold value could not be calculated, but it was estimated to be close to 1. LER was measured here both as the elongation rate of individual leaves, and as a general leaf area expansion rate of the whole plant. Plant leaf area is determined by both the area of individual leaves and the number of leaves, and drought may affect both. We observed that reduction in single leaf expansion and whole plant leaf area occurred at a similar soil-water status. The linear relationship of the relative leaf area to the relative ? r, and the relationship between relative ? l and relative ? r (data not shown) indicate that ? r is probably involved in the control of leaf expansion of quinoa under drought conditions. 4.5 Nitrogen and carbon The interaction between carbon dioxide and nitrate assimilation is of key importance for crop production. In particular, an adequate supply of nitrate for assimilation to amino acids, together with photosynthesized carbon compounds, and their availability for protein synthesis, is essential for metabolism. The supply of nitrate is crucial for leaf growth because of the role of proteins in the growth of cell walls and the cytoskeleton, and hence in cell expansion (Lawlor et al., 1988). Ndeprivation was shown to decrease shoot water potential in barley (Dodd et al., 2002). An increased C-assimilation per unit N would increase biomass and C/N (Lawlor, 2002). We found a high nitrogen content of 5-6%, corresponding to c. 35% protein of newly developed leaves in quinoa. Total N, which was not influenced by drought, was even higher than normally found in the N-fixating legumes. The carbon content was significantly higher in the control plants than in drought-stressed at bud formation, but not at anthesis, and lower than normal for plant material. Also the C/N ratio of 67 was lower than the 14-25 ratio normally reported for plant material on dry weight basis. Under field conditions with slow soil drying it
5
Conclusions
We conclude that during soil drying, quinoa plants at both bud formation and anthesis have a sensitive stomatal closure by which the plants are able to maintain ? l and Amax. This results in an increase of WUE in plants at both bud formation and anthesis. The linear relationship of the relative leaf area to the relative ? r, and the relationship between relative LER and relative ? r indicate that ? r is probably involved in the control of leaf expansion of quinoa under drought conditions. In this study there was no Ndeficiency in the plants, even after a period of severe drought; therefore it is concluded that the effects on leaf behaviour, such as growth and stomata opening, were caused by drought. Soil-water thresholds for gs were significantly lower than that for Amax. Both Amax and gs were affected by a decreasing ? r, Amax less than gs.
Acknowledgements This study was financed by the Danish Agricultural and Veterinary Research Council (SJVF).
References Ali, M., C.R. Jensen and V.O. Mogensen. 1998. Early signals in field grown wheat in response to soil drying. Australian Journal of Plant Physiology, 25, 871-882. Bahrun, A., C.R. Jensen, F. Asch and V.O. Mogensen. 2002. Drought-induced changes in xylem pH, ionic composition and ABA concentration act as early signals in field grown maize (Zea mays L.). Journal of Experimental Botany, 53, 1-13. Boyer, J.S. 1970. Leaf enlargement and metabolic rates in corn, soybean, and sunflower at various leaf water potentials. Plant Physiology 46, 233-235. Clarkson, D.T., L. Williams and J.B. Hanson. 1984. Perfusion of onion root xylem vessels: a method and some evidence of control of the pH of the xylem sap. Planta 162, 361-369 Dodd, I.C., R. Munns and J.B. Passioura. 2002. Does shoot water status limit leaf expansion of nitrogen-deprived barley? J. Exp. Bot. 53, 1765-1770
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Freeden, A.L., Gamon, J.A., Field, C.B., 1991. Resonses of Amax and carbohydrate partitioning to limitations in nitrogen and water availability in field grown sunflower. Plant, Cell and Environ. 14, 963-970. Fromard, L., V. Babib, P. Fleurat-Lessard, J.-C. Fromont, R. Serrano and J.-L. Bonnemain. 1995. Control of vascular sap pH by the vessel-associated cells in woody species. Plant Physiology 108, 913-918 Garcia, M., J.J. Vacher and J. Hidalgo. 1991. Estudio comparativo del comportamiento hidrico de dos variedades de quinua en el altiplano central. In, Actas del VII Congreso Internacional sobre Cultivos Andinos. IBTAOrstom-CIID. La Paz, Bolivia, 57-62 Garcia, M., D. Raes and S.-E. Jacobsen. 2003. Evapotranspiration analysis and irrigation requirements of quinoa (Chenopodium quinoa) in the Bolivian highlands. Agricultural Water Management 60, 119-134. Hartung, W. and J.W. Radin. 1989. Abscisic acid in the mesophyll apoplast and in the root xylem sap of water-stressed plants: the significance of pH gradients. Current Topics in Plant Biochemistry and Physiology 8, 110124 Hartung, W., A. Sauter and E. Hose. 2002. Abscisic acid in the xylem: where does it come from, where does it go to? Journal of Experimental Botany 53, No. 366, 27-32. Henson, I.E., C.R. Jensen and N.C. Turner. 1989. Leaf gas exchange and water relations of lupins and wheat. III. Abscisic acid and drought-induced stomatal closure. Australian J. Plant Phys. 16, 429-442 Jacobsen, S.-E. and A. Mujica. 2001. Quinua:
Lupinus angustifolius 25
Chenopodium quinoa 13
53
39
36
gs 30
3
Chenopodium quinoa
2 Chenopodium Chenopodium quinoa
quinoa 19
Brassica napus
23
37
11
inhibition of leaf elongation but not stomatal conductance. Planta 179, 466-474. Sadras, V.O. and S.P. Milroy. 1996. Soil-water thresholds for the responses of leaf expansion and gas exchange: A review. Field Crops Research 47, 253-266.
68
16 Chenopodium quinoa Solanum juzepczukii
Zea mays 58
68
25
12
Towards the improvement of drought resistance in lupin Jairo A. Palta1,2, Neil C. Turner1,2, Robert J. French2,3 and Bevan J. Buirchell2,4 1
CSIRO Plant Industry, Centre for Environmental and Life Sciences, Private Bag, No. 5 Wembley, WA 6913 Australia. 2 Centre for Legumes in Mediterranean Agriculture, University of Western Australia, Crawley, WA 6009 3 Western Australia Department of Agriculture, Dryland Research Institute, PO Box 432, Merredin, WA 6415, Australia. 4 Western Australia, Department of Agriculture, Locked Bag 4, Bentley, WA 6983, Australia.
Abstract Extent of early flowering and podding, high pod retention, rate of seed filling and degree of assimilate transfer from stem and leaves to seed were determined for 12 lupin genotypes, across three seasons with different intensity of development of terminal drought. Measurements of flowering and podding dates, pod retention, seed growth rate, plant water status, seed yield and its components were made. The timing and intensity of development of the terminal drought was average in 1998 and 1999 and extreme in 2000. In each year, the seed yield under terminal drought showed genotypic differences, which appeared consistent with the timing and intensity of the development of the terminal drought. Early flowering and podding were significantly correlated with seed yield. Pod retention was highly correlated with yield in seasons in which the intensity of development of terminal drought was average, but not under extreme conditions of terminal drought. This was because the seed number per pod was markedly reduced to compensate for the high number of pods retained. The degree of assimilate transfer from stem and leaves to the seed was not correlated with seed yield, suggesting that this parameter is not practical in screening for high yield under terminal drought. Fast rates of seed growth were significantly correlated with high yields regardless of the intensity of development of terminal drought. Measurements of the rates of seed growth were time consuming and only few varieties were able to be examined at one time. Further studies on pod and seed development conducted in 2001 and 2002 showed that across genotypes pods changed their colour from green to khaki 1317 days before the end of the linear phase of seed growth. This allowed concise and easier measurements of the rate of seed growth so that a large number of genotypes were able to be evaluated. Rates of seed growth were also significantly correlated with the length of the pods, suggesting that maximum pod length can be used to select for faster rates of seed filling under terminal drought.
Key words: Lupinus angustifolius; Lupinus luteus; terminal drought; yield; pod retention; seed filling; early flowering; harvest index
E-mail:
[email protected]
1 Introduction Narrow-leafed lupin (Lupinus angustifolius L.) is the most important grain legume crop grown on the acid sandy soils of the Mediterranean climatic region of southern Australia. During the past six years, narrow-leafed lupin was planted on more than 1.0 million ha in Western Australia and annual production exceeded 1.2 million tonnes. Lupin crops are grown during the cool wet winter months and mature during the spring as temperatures and evaporation rates rise and rainfall decreases (Fitzpatrick, 1970; Reader et al., 1995). Consequently, the reproductive growth of the crop is shortened by terminal drought resulting in a reduction in yield (Palta and Dracup, 1994; Dracup et al., 1998; Palta and Plaut ,1999).
Selection has ensured early flowering in narrowleafed lupin (Gladstones, 1994). However, the subsequent vegetative growth of the apical branches often delays the start of pod filling until terminal drought develops (Greenwood et al., 1975; Pate et al., 1980). Pod filling is almost entirely dependent on current assimilation (Pate et al., 1980) and photosynthesis in narrow-leafed lupin is very sensitive to water deficits (Turner and Henson 1989). Thus, pod filling is reduced by a reduction in the availability of current assimilate (Palta and Ludwig, 1996; 2000), that induces pod and seed abortion and reduces seed yield and harvest index. Early flowering and podding, pod retention, seed survival, fast seed filling and high transfer of assimilate to the seed have been considered as some of the key charactetistics for improved yield and
yield maintenace in lupin under terminal drought (Palta et al., 2000). In the present study, these characteristics were studied on 12 genotypes of lupin grown on a fine-textured, acid to neutral soil in the Mediterrnaean climatic region of Western Australia. The aim of the study was to identify and evaluate the morphological and physiological characteristics of lupin that may affect seed yield in these low rainfall environments. After initial results indicated that fast seed growth was a key characteristic for obtaining high yield, we conducted a second study to determine variation among genotypes for this character trait and to develop simple techniques that allow lupin breeders to select for faster rates of seed filling under terminal drought.
2
-1
Materials and methods
2.1 Experimental site
2.2
Experiments were conducted over the growing seasons (May-November) of 1998, 1999 and 2000 at Merredin in the eastern wheatbelt of Western Australia (31o 30’S, 118o
angustifolius Lupinus luteus
Plant material Lupinus
Table 1. List of genotypes grown at Merredin, Western Australia in 1998, 1999 and 2000 under rainfed conditions. All genotypes were Lupinus angustifolius except Wodjil that is of Lupinus luteus Genotype
Category and release date
Merrit
Cultivar-1991
Mayllie Kalya Belara
Cultivar-1995 Cultivar-1996 Cultivar-1997
Tallerack Wodjil
Cultivar-1997 Cultivar-1997
Tanjil Quilinock WALAN 2049 WALAN 2053 WALAN 2072 WALAN 2026
Cultivar-1998 Cultivar-1999 Advanced line Advanced line Advanced line Advanced line
Phomopsis resistant and high yielding, in main lupin growing areas of Western Australia. Moderately resistant to Brown spot. Moderate resistance to anthracnose and later maturing. High yielding, large-seeded and 3-5 days earlier flowering than Merrit. Restricted branching and yield comparable to Merrit. Yellow lupin well adapted to very acid soils. Later flowering than narrow-leafed lupins. Resistant to anthracnose, high yielding. Large-seeded and high yielding. Thin seed coat and high yielding. Restricted branching. High yielding in medium to low rainfall areas. Moderate resistance to anthracnose.
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June in plots 1.44m wide (eight rows, 0.18m apart) and 10m long. The genotypes included the cultivars Belara, Quilinock, Tanjil, Kalya and Merrit (Table 1). At the University of Western Australia Research Station at Shenton Park, six narrow-leafed lupin genotypes putatively differing in seed growth rates were sown on 16 June 2001 in plots 1.44m wide (eight rows, 0.18m apart) and 30m long. The lupin genotypes included the current cultivars Merrit, Belara, Quilinock, Tanjil, Kalya and the advanced breeding line WALAN 2053.
1998 and 94 DAS in 1999) to final harvest (188 DAS in 1998 and 168 DAS in 1999) in order to measure seed development. Seeds from the 3 middle pods on the mainstem were taken each time from 6 plants per plot and after the pods were threshed by hand the seeds and pod shells were redried and weighed. An analysis of seed growth was made with the logistic function using the equation: SDW = A / (1+e (B-Ct) )
(1)
where SDW is the seed weight at t days after 50% flowering whilst the parameters A, B and C define the particular shape of a symmetric function of sigmoidal form. The parameter A, defines final seed dry weight and (ln B)/C) time after flowering that maximum seed growth rate of CA/4 occurs. Duration of seed growth (B+2.944)/C was defined as time required for each seed to reach 95% of its final dry weight. Parameter estimates were obtained using the non-linear regression procedure in Genstat 5 (Payne et al., 1987). Plant samples were also harvested at Merredin in 1999 at weekly intervals from the beginning of pod set (94 DAS) to maturity (168 DAS) for measurements of remobilisation of dry matter to the seeds. Ten plants per plot, including leaf material on the ground, were sampled each time and separated in to leaves, stems, pods, walls and seeds for dry weight determination. All plant parts were oven dried to constant weight and weighed. Dry matter per unit area was calculated from measured dry matter per plant and measured plant density for the corresponding plot. Additionally, all pods set from 10 plants per plot were tagged and counted weekly until final harvest for measurement of pod retention. Means and standard errors were calculated with the Genstat means program and tests for differences among genotypes and treatments were performed using a one- and a two-way ANOVA, respectively. Significant differences (P=0.05) were identified with the l.s.d. test. At the University of Western Australia Research Station in 2001, harvests of seeds from pods on mainstem and first order apical branches were taken from 6 plants per plot at weekly intervals from commencement of podding to final harvest. Rates of seed growth, seed number per pod and seed size was measured as described above. Beginning and end of the linear phase of seed growth was measured for each genotype and morphological characteristics, such as pod length, pod swelling and pod colour were measured to identify easily observable characteristics associated with these stages of the linear phase of seed growth.
2.3 Measurements Rainfall was recorded daily at each experimental site. In addition, daily records of wet and dry bulb air temperature, windspeed and class-A pan evaporation were obtained from an automatic weather station located within 200 m of the experimental plots. The dates of the developmental stages (phenostages) of first flowering, 50% flowering (plants had at least one fully opened flower with visible corolla coloration), first podding, 50% podding (plants had at least one pod projected beyond the petals about 8 mm long) and physiological maturity (95% of leaves and pods had turned yellow) were observed directly in the field on 10 plants per plot. Leaf water potential (? leaf) was measured each year at Merredin near midday (1200-1400 h) on 6 well-illuminated leaves from randomly selected plants from each plot. The measurements were made on clear sunny days at approximately weekly intervals between 105 and 154 DAS in 1998, 90 and 146 DAS in 1999 and 96 to 137 DAS in 2000. Measurements were made using a pressure chamber following the precautions of Turner (1988). Each leaf was excised after covering with a polyethylene bag and was equilibrated in the pressure chamber within 1 min. Replicate analyses agreed within 0.05 MPa. At Merredin each year and at the University of Western Australia Research Station in 2001, harvests of above ground biomass were taken at first podding and at final harvest from a 1 m2 quadrat from each plot. On each occasion, sampling sites were assigned randomly and plant material was cut at the soil surface, dried in a fan-forced oven at 70oC and weighed. Where appropriate pods were counted, threshed by hand, seed and pod shells redried, and weighed. Seed number was counted and 1000-seed weight was determined for each sample. At least 1 m length of crop was left between sampling areas to minimize edge effects on the adjacent sampling area. At Merredin in 1998 and 1999, additional harvests of seeds were taken at weekly intervals from the commencement of podding (97 DAS in
3 Results Meteorological data are presented for each year at Merredin in Figure 1. Over the three years genotypes matured in the period 146-188 DAS. The total
3
Rainfall (m m )
Rainfall (m m )
Evaporation Tem perature (C) (m m )
Rainfall (m m )
Evaporation Tem perature (C) (m m )
Evaporation Tem perature (C) (m m )
rainfall during the growing season was 217 mm in 1998, 160 mm in 1999 and 110 mm in 2000. From the time that plants were at 50% flowering until they reached maturity, rainfall was 57 mm in 1998, excluded from the crops by the use of a rainout shelter in 1999 and less than 1 mm in 2000. At the same time, pan evaporation increased to 6 mm day-1 in 1998, 6.5 mm day-1in 1999 and 7 mm day-1in 2000. There were some periods when minimum temperatures fell 0oC. For instance in 1999 there were seven occasions, five of them around flowering, and in 2000 there were four occasions during vegetative growth. The genotypes flowered and filled their seeds under drier and hotter conditions in 2000 compared to 1998 and 1999. Fifty percent flowering on the mainstem occurred as early as 84 DAS or 1100 Co d in Belara in 1999 and as late as 104 DAS or 1360 Co d in Wodjil in 1998 (Table 2). Flowering in Belara and Quilinock was earlier than in the other genotypes in each year. Belara and Quilinock flowered 5-6 days ahead of Merrit in 1998 and 2000, and 10 days ahead in 1999. Wodjil flowered 7 days later than Merrit in 1998, but at the same time as Merrit in 1999. In each year 50% podding on the mainstem occurred 8-9 days after 50% flowering in most of the genotypes except in Wodjil and WALAN 2053, in which it occurred 12-15 days after 50% flowering. ? leaf in Wodjil was higher than in the other genotypes (Figure 2a and b). At podding in 1998, ? leaf in Wodjil was ? ?
Tim e ofthe year
Figure 1 Maximum (
and evaporation ( at Merredin, Western Australia during the growing seasons of (a, b) 1998, (c, d) 1999 and (e, f) 2000. The time of 50% flowering on the mainstem is indicated by the vertical arrow.
Table 2. Days after sowing (DAS) for 50% flowering and 50% podding on the mainstem for lupin genotypes grown at Merredin, Western Australia in 1998, 1999 and 2000 1998
Genotypes
Merrit Belara Tallerack WALAN 2049 Mayllie Wodjil Quilinock Kalya Tanjil WALAN 2053 WALAN 2072 WALAN 2026 l.s.d (P< 0.05)
Flowering (DAS) 97 92 99 97 96 104 4
Podding (DAS) 105 101 107 105 105 119 2
1999 Flowering (DAS) 94 84 93 84 90 91 89 89 90 4
2000 Podding (DAS) 102 91 107 92 99 100 101 99 99 3
At podding in 1999, ? leaf in all the genotypes was about -1
?
4
Flowering (DAS) 91 85 86 90 91 3
Podding (DAS) 99 93 94 98 99 4
HI than Merrit (Table 3). The greater seed yield of Belara, Tallerack and WALAN 2049 was associated with faster rates of seed growth, which in Belara and WALAN 2049 resulted in larger seeds than Merrit. In contrast, seed size in Tallerack was similar to Merrit.
In 1999 the final biomass was higher than in 1998, but seed yields were similar. The biomass was significantly higher in Tanjil, Quilinock, Belara and WALAN 2053 than in Merrit (Table 4) while the biomass of the other five genotypes was not significantly different from Merrit. The seed yield of cultivars Belara, Quilinock and Tanjil were 30%, 34% and 48%, higher, respectively, than that of Merrit. None of the ad-vanced breeding lines had seed yields that exceeded the yields of Belara, Quilinock and Tanjil. The HI of all genotypes was similar to that of Merrit, except for Wodjil, which had a lower HI. The cultivar Quilinock and Tanjil had a maximum pod retention of 80%. All the advanced breeding lines had low pod retention
D a ys a fte r so w in g
-0 .0
90
105
120
135
150
165
a)
-0 .5 -1 .0 -1 .5 -2 .0 -2 .5
Leafw aterpotential(M Pa)
-0 .0
d)
1999
Genotype
-0 .5 -1 .0 -1 .5 -2 .0
Biomass (t/ha)
Merrit
Seed Yield (t/ha) 1.5
5.5
28
Tanjil
2.3
8.4
28
80
Quilinock
2.0
7.5
28
80
67
HI (%)
Pod retention (%) 62
Belara
2.0
7.4
28
-2 .5
WALAN2053
1.9
7.3
27
69
- 0 .0
Kalya
1.8
6.5
28
75
WALAN2026
1.7
6.4
28
63
WALAN2072
1.7
6.5
27
66
Wodjil
1.3
6.2
21
32
l.s.d(P
