(Ritchie, Hanway, Thompson, & Benson, 1994; Smit, 2000:9). ...... without causing important reductions in grain yield (Strydom, Bennie, van Rensburg.
EFFECTS OF SOIL WATER AVAILABILITY AND PLANTING DENSITY ON THE GRAIN YIELD OF SOYA BEANS [Glycine max (L.) Merrill]
by
ERIC NEMAKHAVHANI NDOU
Submitted in partial fulfillment of the requirements for the degree
MAGISTER TECHNOLOGIAE: AGRICULTURE
in the
Department of Crop Sciences
FACULTY OF SCIENCE TSHWANE UNIVERSITY OF TECHNOLOGY
Supervisor: Prof W Van Averbeke
November 2006
DECLARATION
“I hereby declare that the dissertation submitted for the degree M Tech: Agriculture, at the Tshwane University of Technology, is my original work and has not been previously submitted to any other institution of higher education. I further declare that all sources cited or quoted are indicated and acknowledged by means of a comprehensive list of references”.
E.N. Ndou
Student number: 99005149
Copyright© Tshwane University of Technology 2006 i
DEDICATION
This manuscript is dedicated to my beloved mother, Mmbadi Thivhonali Gladys, who passed away before its completion. Ndi a livhuwa u aluswa, u dzheniswa tshikilo, ţhuţhuwedzo na lufuno lwevha sumbedza sa mubebi. Ndi do vha elewa misi yoţhe.
ii
ACKNOWLEDGEMENTS
I thank God, the Almighty, for the strength and protection he provided me with throughout the study.
I would like to express my sincere gratitude to Prof W Van Averbeke for his keen supervision, suggestions and support throughout the study and to Prof PJ Jansen van Vuuren, the Head of the Department of Crop Sciences, for providing me with facilities, research equipment and implements on the Research Farm.
I am also grateful to The National Research Foundation, the Research Committee of the Faculty of Agricultural Sciences and the Tshwane Nutrition Project for their financial support towards my work and to the Monsanto (Sensako) Seed Company for supplying and delivering, free of charge, the SNK 500 seed that was used in the 2002/03 experiment.
My thanks are also due to Dr B Eisenberg for providing me with advice and assistance during the statistical analysis of my data, Mrs F Mahlangu for her assistance in accessing information in the TUT library and Mr G de Nysschen of the ARC-ISCW for his assistance with the climatic data.
iii
I acknowledge Mr FK Khangale, Mr AI Ntho, Mr P Moila, Mr MN Fihla, Mr A Nyamela and Ms L Sibeko and particularly Mr ZM Sosibo, who all helped me at one stage or another with the work in the field or in the laboratory.
I also wish to thank Mr D Mfolo and the staff at the TUT Research Farm for their assistance with field preparation.
My appreciation also goes to Dr MA Smit of the SA Sugar Research Institute and to Mr AJ de Lange, Dr AJ Liebenberg and Mr GP de Beer of the ARC-Grain Crops Institute for their valuable advice during the course of this study. I would also like to thank my friends whose love, encouragement and support gave me the inspiration until the end of my study.
Last but not least, I am indebted to my parents (Mmbangiseni and the late Thivhonali) for their words of encouragement and support.
iv
ABSTRACT
The current study investigated interaction effects between soil water availability and planting density on the grain yield of soya beans [Glycine max (L.) Merrill] for the purpose of refining the existing planting density recommendations for local use. A factorial experiment involving a split-plot design with soil water availability as main plot treatment and planting density as split-plot treatment was conducted during the 2002/03 and 2003/04 summers. Three soil water availability treatments and planting densities ranging from 5 plants m-2 to 80 plants m-2 were employed. Overall, the study confirmed existing theory that describes soil water availability and planting density relationships in soya beans. In the 2002/03 experiment, which was defoliated by a hail storm, only planting density had a statistically significant effect on grain yield, whilst in the 2003/04 experiment, the effects of soil water availability, planting density and their interaction were significant. In both experiments, the increase in grain yield obtained by raising planting density was primarily due to an increase in the number of pods per unit area and number of seeds per unit area, whilst other yield components were less affected. In the 2003/04 experiment the interaction effect between soil water availability and planting density was statistically highly significant.
v
TABLE OF CONTENTS PAGE DECLARATION
i
DEDICATION
ii
ACKNOWLEDGEMENTS
iii
ABSTRACT
v
TABLE OF CONTENTS
vi
LIST OF FIGURES
ix
LIST OF TABLES
xiv
LIST OF SYMBOLS AND ABREVATIONS
xix
LIST OF APPENDICES
xxiii
CHAPTER ONE 1
INTRODUCTION
1
CHAPTER TWO 2
REVIEW OF LITERATURE
5
2.1
Physiological and agronomic characteristics of soya beans
5
2.2
Effect of planting density and spacing on the growth and yield of soya beans
2.3
Effect of soil water availability on the growth and yield of soya beans
2.4
Planting density and soil water availability interaction effects on the growth and yield of soya beans
8 13
15
vi
2.5
2.6
Southern African perspectives on planting density and soil water availability effects in soya beans
16
Conclusions
17
CHAPTER THREE 3
MATERIAL AND METHODS
19
3.1
Introduction
19
3.2
Description of the study site
19
3.3
Experimental procedures
27
3.3.1
General procedures
27
3.3.2
Specific procedures that applied to the 2002/03 experiment
31
3.3.3
The 2003/04 experiment
37
CHAPTER FOUR 4
RESULTS AND DISCUSSION
40
4.1
Introduction
40
4.2
The 2002/03 experiment
40
4.2.1
Conditions during the growing season
40
4.2.2
Water
41
4.2.3
Leaf area development
47
4.2.4
Grain yield
49
4.2.5
Yield components
52
4.3
The 2003/04 experiment
60
vii
4.3.1
Conditions during the growing season
60
4.3.2
Water
62
4.3.3
Leaf area development
67
4.3.4
Grain yield
69
4.3.5
Yield components
71
4.4
Summary of the findings
80
CHAPTER FIVE 5
CONCLUSIONS
85
REFERENCES
87
APPENDICES
99
viii
LIST OF FIGURES PAGE FIGURE 1.1:
Area planted to soya beans in South Africa and total production during the period 1970-2003 (National Department of Agriculture, 2004:19)
FIGURE 2.1:
Effect of planting density and soil water availability on the grain yield of soya beans after Elmore (1998)
FIGURE 3.1:
21
Map of the City of Tshwane showing the location of Honingnestkranz
FIGURE 3.4:
20
Map of Gauteng Province showing the location of the City of Tshwane
FIGURE 3.3:
15
Map of South Africa showing the location of Gauteng Province
FIGURE 3.2:
2
22
Map of Honingnestkranz showing the location of the TUT Research Farm
23
ix
FIGURE 3.5:
Estimated mean daily evapotranspiration (mm) by soya beans planted on 1 November at Roodeplaat using the procedures of Green (1985)
FIGURE 3.6:
A water meter with accuracy of 1litre was used to measure the amount of irrigation water applied to the plots
FIGURE 3.7:
32
The bridge that was used during thinning and weed control in the high planting density treatments
FIGURE 4.1:
29
View of the level basins used to maintain the high water (HW) and intermediate water (IW) treatment
FIGURE 3.8:
25
35
(a) The 2002/03 experiment a few hours before the hailstorm occurred (61 DAP); (b) the experiment the day after the hailstorm damage (63 DAP); (c) close view of the hail damage to the soya bean plants in the low planting density treatment (10 plants m-2, 63 DAP); (d) plants showing remarkable recovery from the hail damage by producing a new flush of leaves (high planting density treatment, 84 DAP)
41
x
FIGURE 4.2:
Comparison of the total weekly amounts of water supplied to the high water (HW) treatment with the expected crop evapotranspiration estimated using the procedures described by Green (1985:6, 33) in the 2002/03 experiment
FIGURE 4.3:
42
Comparison of the total weekly amounts of water supplied to the intermediate water (IW) treatment with the expected crop evapotranspiration estimated using the procedures described by Green (1985:6, 33) in the 2002/03 experiment
FIGURE 4.4:
43
Comparison of the total weekly amounts of water supplied to the low water (LW) treatment with the expected crop evapotranspiration estimated using the procedures described by Green (1985:6, 33) in the 2002/03 experiment
FIGURE 4.5:
Effect of planting density on leaf area index of soya beans in the high water (HW) treatment of the 2002/03 experiment
FIGURE 4.6:
44
48
The interaction between planting density and water levels on the grain yield of soya beans in the 2002/03 experiment
51
xi
FIGURE 4.7:
From emergence until 60 days after planting (DAP), water stress negatively affected growth of the soya bean plants in the low water (LW) treatment as is shown here for the highest planting density treatment (80 plants m-2) 56 DAP
FIGURE 4.8:
61
View of soya bean plants in the lowest planting density treatment (5 plants m-2) in the low water (LW) treatment 56 DAP
FIGURE 4.9:
61
Comparison of the total weekly amounts of water supplied to the high water (HW) treatment with the expected crop evapotranspiration estimated using the procedures described by Green (1985:6, 33) in the 2003/04 experiment
FIGURE 4.10:
62
Comparison of the total weekly amounts of water supplied to the intermediate water (IW) treatment with the expected crop evapotranspiration estimated using the procedures described by Green (1985:6, 33) in the 2003/04 experiment
FIGURE 4.11:
63
Comparison of the total weekly amounts of water supplied to the low water (LW) treatment with the expected crop evapotranspiration estimated using the procedures described by Green (1985) in the 2003/04 experiment
65
xii
FIGURE 4.12:
Effect of planting density on leaf area index of soya beans in the high water (HW) treatment of the 2003/04 experiment
FIGURE 4.13:
68
The interaction between planting density and water levels on the grain yield of soya beans in the 2003/04 experiment
70
xiii
LIST OF TABLES PAGE TABLE 2.1:
Vegetative and reproductive stages of soya bean plants (after Fehr and Caviness, 1977)
TABLE 2.2:
Effect of planting density on the grain yields and yields components of soya beans after Board (2000)
TABLE 2.3:
6
12
Effects of soil water availability on growth and yield of soya beans during different reproductive (R) stages of growth after Ritchie et al. (1994)
TABLE 2.4:
Effect of planting density on soya beans grain yield (after Seed Co., SA)
TABLE 3.1:
14
17
Summary of climatic variables recorded at the Roodeplaat Agricultural Research Station over a period of 45 years (after ARC-ISCW, 2005)
TABLE 3.2:
24
Plant spacing and equivalent planting densities used in the 2002/03 and 2003/04 soya bean experiments
31
xiv
TABLE 3.3:
Chemical properties of the topsoil at the site of the 2002/03 experiment before the experiment was planted and after it was harvested
TABLE 3.4:
Chemical properties of the topsoil at the 2003/04 experimental site
TABLE 4.1:
33
38
Weekly amount of rainfall received at the experimental site during the growing period of soya beans in the 2002/03 experiment
TABLE 4.2:
Weekly amount of irrigation applied to the different water treatments in the 2002/03 soya bean experiment
TABLE 4.3
47
Effect of planting density and soil water availability on the grain yield of soya beans in the 2002/03 experiment
TABLE 4.5:
46
Mean total amount of water recorded for the different treatments in the 2002/03 experiment
TABLE 4.4:
46
50
Effect of planting density and soil water availability on the number of soya bean pods plant-1 in the 2002/03 experiment
52
xv
TABLE 4.6:
Effect of planting density and soil water availability on the number of soya bean pods per unit area in the 2002/03 experiment
TABLE 4.7:
Effect of planting density and soil water availability on the number of soya bean seeds plant-1 in the 2002/03 experiment
TABLE 4.8:
54
55
Effect of planting density and soil water availability on the number of soya bean seeds per unit area in the 2002/03 experiment
TABLE 4.9:
Effect of planting density and soil water availability on the number of soya bean seeds pod-1
TABLE 4.10:
58
Effect of planting density and soil water availability on the mass of 100 soya bean seeds in the 2002/03 experiment
TABLE 4.11:
57
59
Weekly amount of rainfall received at the experimental site during the growing period of soya beans in the 2003/04 experiment
TABLE 4.12:
66
Weekly amount of irrigation applied to the different water treatments in the 2003/04 soya bean experiment
66
xvi
TABLE 4.13:
Mean total amount of water recorded for the different treatments in the 2003/04 experiment
TABLE 4.14:
Effect of planting density and soil water availability on the grain yield of soya bean in the 2003/04 experiment
TABLE 4.15:
67
69
Effect of planting density and soil water availability on the number of soya bean pods per plant in the 2003/04 experiment
TABLE 4.16:
72
Effect of planting density and soil water availability on the number of soya bean pods per unit area in the 2003/04 experiment
TABLE 4.17:
74
Effect of planting density and soil water availability on the number of soya bean seeds per plant in the 2003/04 experiment
TABLE 4.18:
75
Effect of planting density and soil water availability on the number of soya bean seeds per unit area in the 2003/04 experiment
76
xvii
TABLE 4.19:
Effect of planting density and soil water availability on the number of soya bean seeds per pod in the 2003/04 experiment
TABLE 4.20:
77
Effect of planting density and soil water availability on the seed mass (100 seeds) of soya beans in the 2003/04 experiment
TABLE 4.21:
78
Summary of the results obtained in the 2002/03 and 2003/04 soil water availability x planting density experiments with soya beans in Pretoria
81
xviii
LIST OF SYMBOLS AND ABREVATIONS
AGB
Above-ground biomass
ANOVA
Analysis of variance
AP
After planting
ARC-ISCW
Agricultural Research Council - Institute for Soil, Climate and Water
Ca
Calcium
CGR
Crop growth rate
cm
Centimetre
cmol(+) kg-1
Centimol positive charge per kilogramme soil
CWU
Consumptive water use
DAP
Days after planting
Eto
Reference crop evapotranspiration
Evap.
Evapotranspiration
FSSA
Fertilizer Society of South Africa
g
Gramme
g m-2
Gramme per square metre
GY
Grain yield
ha-1
Per hectare
Hr day-1
Hour per day
HW
High water treatment
IW
Intermediate water treatment
K
Potassium
xix
kg
Kilogramme
kg ha-1
Kilogramme per hectare
kg m-3
Kilogramme per cubic metre
kg P ha-1
Kilogramme phosphorus per hectare
km
Kilometre
km/day
Kilometre per day
LAGR
Leaf area growth rate
LAI
Leaf area index
LSD
Least Significant Difference
LW
Low water treatment
m
Metre
m2
Square metre
Mg
Magnesium
mg kg-1
Milligramme per kilogramme
mg P kg-1
Milligramme phosphorus per kilogramme soil
mm
Millimetre
mm day-1
Millilitre per day
N
Nitrogen
Na
Sodium
NAR
Net assimilation rate
NSD
Non significant difference
o
Degree Celsius
C
P
Phosphorus
xx
PAWC
Profile available water capacity
pHwater
pH measured in water
plant-1
Per plant
Pod-1
Per pod
R
Reproductive stage
R1
Start of flowering stage
R2
Full flowering stage
R3
Start of pod formation stage
R4
Full pod formation stage
R5
Start of seed formation stage
R6
Full seed development stage
R7
Start of maturing stage
R8
Full maturity stage
SAS®
Statistical Analysis Software
Seed-1
Per seed
T
Temperature
t ha-1
Ton per hectare
TUT
Tshwane University of Technology
USA
United States of America
V
Vegetative stage
V (n)
nth node stage
V1
First node stage
V2
Second node stage
xxi
V3
Third node stage
V4
Fourth node stage
V5
Fifth node stage
VC
Cotyledon stage
VE
Emergence stage
WAP
Weeks after planting
xxii
LIST OF APPENDICES PAGE APPENDIX A1:
Description of the soil profile of the Hutton Ventersdorp soil at the TUT Research Farm (Bon Accord, Tshwane)
APPENDIX A2:
Analytical data for the Hutton Ventersdorp type soil at the TUT Research Farm
APPENDIX B:
99
100
Leaf area index of the 2002/03 and 2003/04 planting density x soil water availability soya beans experiment
101
TABLE B1:
Leaf area index values, 2002/03 experiment
101
TABLE B2:
Leaf area index values, 2003/04 experiment
101
APPENDIX C:
Analysis of variance of the 2002/03 and 2003/04 planting density x soil water availability soya beans experiment
TABLE C1:
Analysis of variance for grain yield of soya bean, 2002/03 experiment
TABLE C2:
102
102
Analysis of variance for number of soya bean pods plant-1, 2002/03 experiment
103
xxiii
TABLE C3:
Analysis of variance for number of soya bean pods m-2, 2002/03 experiment
TABLE C4:
Analysis of variance for number of soya bean seeds plant-1, 2002/03 experiment
TABLE C5:
106
Analysis of variance for grain yield of soya bean, 2003/04 experiment
TABLE C10:
105
Analysis of variance for consumptive water use of soya bean, 2003/04 experiment
TABLE C9:
105
Analysis of variance for 100 seed mass of soya bean, 2002/03 experiment
TABLE C8:
104
Analysis of variance for number of soya bean seeds pod-1, 2002/03 experiment
TABLE C7:
104
Analysis of variance for number of soya bean seed m-2, 2002/03 experiment
TABLE C6:
103
106
Analysis of variance for number of soya bean pods plant-1, 2003/04 experiment
107
xxiv
TABLE C11:
Analysis of variance for number of soya bean pods m-2, 2003/04 experiment
TABLE C12:
Analysis of variance for number of soya bean seeds plant-1, 2003/04 experiment
TABLE C13:
108
Analysis of variance for number of soya bean seeds pod-1, 2003/04 experiment
TABLE C15:
108
Analysis of variance for number of soya bean seeds m2, 2003/04 experiment
TABLE C14:
107
109
Analysis of variance for seed mass (100 seeds), 2003/04 experiment
109
xxv
CHAPTER ONE 1 INTRODUCTION The soya bean plant [Glycine max (L.) Merrill] is an annual summer legume that belongs to the Fabaceae family. It is probably the most important legume in the world. As with other members of this family, it bears its seed in pods. The crop is thought to be indigenous to Manchuria, China, where it has been utilised as a food from about 2500 BC (Smit, 2000:6). In the United States, soya beans were introduced as hay and forage crop, but it became increasingly important as an oil and protein meal seed crop during the 19th century. Towards the end of the 20th century, the United States of America was the world’s largest producer of soya beans (Hume, Shanmugasundaram & Beversdorf, 1985:391 and Smit, 2000:6). According to Smit (2000:6) the first South African report on soya beans is found in the Cedara Memoirs of 1903. Poor germination and shattering of pods experienced in initial trials lead to the implementation of a breeding programme at the Agricultural Research Station in Potchefstroom during the early 1950s. This programme resulted in the development of varieties that were adapted to local conditions and no longer shattered prematurely. Production of soya beans in South Africa remained localised and relatively unimportant until the early 1970s, when soya beans were incorporated in a rotation with wheat on land where irrigation was available (Smit, 2000:6).
Soya beans play an important role in human and animal nutrition. They contain about 40 % protein, which is of excellent quality and digestibility. They are also a good source of energy and fatty acids for animals (Smit, 2000:3). Commercially, the value of soya beans is further enhanced by the use of the crop as a raw material for a wide
1
range of applications. Important products derived from soya beans are protein meal (about two-thirds of total world consumption) and edible oil (just over a quarter of world consumption). The crop also has many applications in the human food and nutrition sector and in the chemical industry (Smit, 2000:3).
Relative to other parts of the world, especially in Asia, the production of soya beans in South Africa is relatively new. Some 35 years ago, less than 10 000 ha were planted to the crop. Since then, production has increased considerably, especially during the last 15 years (Figure 1). In 2002/03, about 100 000 ha were planted to soya beans in South Africa, producing a grain yield that exceeded 120 000 tons.
Area
180 160
Production
140 120 100 80 60 40
2002/03
1998/99
1994/95
1990/91
1986/87
1982/83
1978/79
1974/75
20 0 1970/71
Area planted (x1000 ha) and Production (x1000 t)
200
Years
FIGURE 1.1: Area planted to soya beans in South Africa and total production during the period 1970-2003 (National Department of Agriculture, 2004:19)
Despite the substantial increase in local production, South Africa remains an importer of soya beans. In 2002, the country imported about 0.9 million tons of soya bean oil
2
cake (National Department of Agriculture, 2004:89) demonstrating that local production still does not meet the national demand.
Local soya bean production may be increased by expanding the area planted to the crop, or by improving its management on existing land. The current study seeks to make a contribution to improved management of the crop. Its focus is on tailoring planting density in soya beans to the expected availability of soil water during the growing season. According to De Beer (2002) and Smit (2003) the existing planting density guidelines in local soya bean production are useful approximations, but they are still subject to refinement.
Experience elsewhere has shown that optimizing planting density in soya beans to suit a particular set of growing conditions such as climate, nutrient availability and row spacing may increase bean yields by 5 to 15 % (Duncan, 1986; Ethredge, Ashley & Woodruff, 1989; Board, Kamal & Harville, 1992; Egli, 1994). Many factors affect optimum plant population density, but there is no doubt that water availability is among them (Taylor, 1980; Graterol, Elmore & Eisenhauer, 1996; Elmore, 1998). By investigating the interactions between water availability and planting density, the current study seeks to contribute to the refinement of existing guidelines for planting density in local soya bean production.
The purpose of the study was to contribute to knowledge aimed at increasing the yield of soya beans obtained by South African farmers by refining existing planting density recommendations for different levels of soil water availability.
The specific
objectives of the study were to empirically determine the response of soya beans to
3
planting density at different levels of water, and to investigate the possible interaction between these two factors. The hypothesis of the study was that “grain yield of soya beans is subject to a positive interaction between soil water availability and planting density”.
The study delimitations were that the experiment was conducted at a single site over a period of two years only. Two different cultivars with similar growth habits were used as test crops (one cultivar per season). Soil water availability was not monitored during the growing season, but gravimetric samples were taken at planting and at harvest and water application to the different water treatments was recorded, enabling the estimation of total consumptive water use during the growing season in each of these treatments. Leaf area development of the soya bean plants was monitored in the high water treatment only.
4
CHAPTER TWO
2 REVIEW OF LITERATURE
2.1 Physiological and agronomic characteristics of soya beans
Soya beans are photoperiodic and are known as quantitative short-day plants. The main effect of day length on soya bean development is that of flowering induction. Reduction in day length triggers the onset of the reproductive stage (Norman, 1978; Farias, 1994; Smit, 2000:9).
Soya bean varieties are categorised in several ways. One of these is growth habit. There are two types of soya bean varieties, namely determinate and indeterminate. In determinate varieties vegetative growth is terminated by the onset of flowering and the growth tip ends in a pod-bearing raceme, a short, stem-like structure that produces flowers and later on pods along its length. Varieties with an indeterminate growth habit develop flowers and form pods simultaneously and over an extended period (Ritchie, Hanway, Thompson, & Benson, 1994; Smit, 2000:9).
Smit (2000:10)
reports that South African soya bean varieties are further subdivided into three maturity classes based on their time to maturity. Short, medium and long growth period varieties are identified.
During its development, soya beans pass through different growth stages. Fehr and Caviness (1977) divide the growth stages of soya beans into two main stages, namely,
5
vegetative and reproductive, as illustrated in Table 2.1. In a stand a growth stage is reached when 50 % of the plants are at or past that particular stage of development.
TABLE 2.1: Vegetative and reproductive stages of soya bean plants (after Fehr and Caviness, 1977)
Vegetative stages
Reproductive stages
Stage no
Stage description
Stage no
Stage description
VE
Emergence
R1
Start of flowering
VC
Cotyledon
R2
Full flowering
V1
First node
R3
Start of pod formation
V2
Second node
R4
Full pod formation
V3
Third node
R5
Start of seed formation
V4
Fourth node
R6
Full seed development
V5
Fifth node
R7
Start of maturing
V (n)
nth node
R8
Full maturity
Soya bean development is sensitive to environmental factors. These include soil type, pests and diseases, wind, light, temperature and water (Ritchie et al., 1994). Water use by soya beans varies with climatic conditions, management practices and length of growing season (Whigham & Minor, 1978; Weiss, 1983; Farias, 1994). In South Africa soya beans can be grown successfully in areas where the mean annual rainfall exceeds 600 mm (Smit, 2000:4).
Soya beans are tolerant to a wide range of soil conditions, but they favour a deep, well-drained fertile soil with a high water holding capacity. An optimum pHwater of 6.0 to 6.5 is desirable, but soya beans can tolerates pH levels ranging between 5.2 and 6
7.5. The crop can be grown successfully on heavy clay soils and sandy soils. In general, soya beans can be produced successfully in areas where maize is grown (Weiss, 1983; Fertilizer Society of South Africa, 1989:187; Smit, 2000:16).
Soya beans are best described as a weakly tap-rooted crop. The taproot gives rise to many lateral roots in the top 30 cm of the soil profile. In highly compacted soils soya beans produce short plants with restricted root development. In conditions where soil compaction is not a limiting factor, soya bean taproots may reach depths exceeding 1.5 m (Weiss, 1983; Gazzoni, 1994; Smit, 2000:7).
Soya beans develop well under a wide range of temperatures. The minimum and maximum temperatures for soya bean growth are 10 0C and 40 0C, respectively. The optimum temperature for growth is 25 0C.
Regions where the mean monthly
temperature of the warmest month is less than 20 0C are considered poorly suited for soya bean production (Farias, 1994; Smit, 2000:16).
Soya bean seeds are borne in pods. The pods contain one to four seeds (Smit, 2000:7). According to Gazzoni (1994) and Smit (2000:8), average grain mass of soya beans ranges between 12 g and 25 g per 100 seeds. Differences in seed mass among varieties do not necessarily affect grain yield. Depending on the cultivar, planting density and growing conditions, a single plant can bear from three to 350 pods (Gazzoni, 1994; Smit, 2000:7).
7
2.2 Effect of planting density and spacing on the growth and yield of soya beans
The growth of plants is studied by means of growth analysis (Hicks, 1978). Growth analysis involves the measurement of plant growth in terms of net assimilation rate (NAR), leaf area growth rate (LAGR), and crop growth rate (CGR) (Barnes & Beard, 1992:17). The purpose of growth analysis is to investigate relationships between these variables over time (Barnes & Beard, 1992:17). CGR is defined as the increase in biomass per unit time. CGR is a function of NAR and leaf area index (LAI). NAR is the increase in biomass per unit of assimilatory material per unit time. LAI is the leaf area of the plants per unit soil surface area (Hicks, 1978; Barnes & Beard, 1992:17).
Grain yield in soya beans is closely related to CGR (Shibles & Weber, 1966). NAR in soya beans declines as LAI increases, because leaf development gives rise to selfshading of the lower leaves. CGR, on the other hand, increases as LAI increases (Hicks, 1978). Generally, CGR of soya beans increases during the first 50 to 60 days after planting until the onset of the flowering (R1) stage and declines thereafter (Buttery as cited by Hicks, 1978).
As planting density increases, light interception per plant decreases, but total light interception per unit ground area increases. A reduction of light interception reduces leaf area and above-ground biomass (AGB) per plant, but increases leaf area and AGB per unit area (Board, Kamal & Harville, 1992; Board & Harville, 1992; Board, 2000).
8
Grain yield of soya beans is the product of several components, namely, number of pods per plant, number of seeds per plant, number of seeds per pod, seed mass and number of plants per unit area (Lehman & Lambert as cited by Tudor-Owen, 1978:4; Ritchie et al., 1994). The grain yield of soya beans is described by equation 1.
GY = No plants m-2 x No pods plant-1 x No of seeds pod-1 x Mass seed-1
equation 1
whereby GY
= grain yield of soya beans expressed in g m-2
No plants m-2
= planting density expressed as mean number of plants m-2
No pods plant-1
= mean number of pods plant-1
No of seeds pod-1
= mean number of seeds pod-1
Mass seed-1
= mean seed mass expressed in g
Generally, research on the effect of planting density on the yield of soya beans grown in the United States shows that grain yield increases as planting density is raised until an optimum is reached, and that increasing planting density in excess of the optimum brings about a decline in grain yield (Wright, Shokes & Sprenkel, 1984; Moore and Longer, 1987; Board, 2000). One of the reasons for grain yield to decline when planting density exceeds the optimum is an increase in lodging (Cooper, 1971; Boquet, 1990). Grain yield in soya beans is a function of LAI, and LAI is a function of planting density (Shibles & Weber, 1965; Board, Kamal & Harville, 1992; Browde, Pedigo, Owen & Tylka, 1994; Grymes, Griffin, Boethel, Leonard, Jordan & Russin, 1999).
9
Increasing planting density reduces the time needed by the crop to develop a canopy that intercepts 95 % of the available light at which CGR is expected to be optimal. In soya beans interception of 95 % of the available light occurs at LAI values of 3.5 to 4 (Shibles & Weber, 1965; Board, Kamal & Harville, 1992; Board & Harville, 1992; Board, Weir & Boethel, 1997; Board, 2000). Shibles & Weber (1966) contend that soya beans produce optimum grain yield when they attain the critical LAI of 3.5 to 4.0 by the time they reach developmental stages R2 to R5. Duncan (1986), on the other hand, argues that optimum-planting density for grain yield coincides with the planting density that produces maximum AGB at the time of flower initiation. This means that differences in grain yield of soya beans due to differences in planting density are established during the V stages and early R1 stage, and not during the R2 – R7 stages of growth (Duncan, 1986; Elgi, 1988). As a result, the optimum planting density for grain yield may well be above that required to achieve 95% light interception at full leaf development (Duncan, 1986; Elgi, 1988; Board, Kamal & Harville, 1992).
The response of soya beans to planting density is essentially a function of variability in the number of pods per unit area, which, in turn, is a function of the number of fertile nodes (Board, Kamal & Harville, 1992). The number of pods and seeds per plant represent the size of the assimilate sink during reproductive growth. Increasing planting density and narrowing the spacing cause a reduction in the number of pods per plant (Enyi, 1973). Several studies have shown that whereas the number of pods and seeds plant-1 decrease with increasing plant density, they increase per unit area (Enyi, 1973; Tudor-Owen, 1978:31; Elgi, 1988; Ethredge, Ashley & Woodruff, 1989). Planting density and row spacing do not affect the number of seeds pod-1 in
10
soya beans (Enyi, 1973; Tudor-Owen, 1978:55; Ikeda, 1992) and they appear to have a limited effect on seed mass. Enyi (1973), Tudor-Owen (1978:55) and Taylor (1980) report an increase in seed mass when plant spacing was widened, but Chapman (1987), Egli (1988), Ethredge, Ashley and Woodruff (1989) and Board (2000) failed to record a response in seed mass to variability in plant spacing.
Research in the USA has also shown that the relationship between grain yield and planting density in soya beans is subject to considerable variation. Board and Harville (1992) report that when planting density is kept constant, equidistant spacing increases LAI and light interception during the vegetative stages and early reproductive stages. According to these authors, grain yields were achieved that are higher than those obtained when spacing is not equidistant. Similarly, Board, Kamal and Harville (1992) show that when planting density is kept constant, narrowing the row spacing increases light interception and grain yield in soya beans. However, Wells (1991) points out that the advantage of narrowing rows, which results in more equidistant plant spacing, occurs primarily during the early part of the season, when it brings about a reduction in competition among plants within the row. This increases total biomass, but not necessarily grain yield. Examining four planting density and row width combinations in soya beans, Wells (1991) recorded differences in total biomass yield among the treatments that were statistically significant, but the differences in grain yield among the treatments were not. Chapman (1987) points out that soya bean plants have the ability to fill the available space around them by producing lateral branches, which results in a similar number of nodes per unit area being produced over a range of planting densities. The ability of a soya bean plant to adapt its development in terms of number of lateral branches to the available space is
11
probably one of the factors that explain the absence of substantial differences in grain yield among different planting density treatments that were observed in some studies.
Cultivar is another factor that affects the relationship between grain yield and planting density in soya beans.
Tudor-Owen (1978:58) reports that grain yield of both
determinate and indeterminate cultivars peaks at a density of 40 plants m-2. Egli (1988, 1994) disagrees. He argues that determinate and indeterminate soya bean cultivars differ in their response to planting density. He reports that determinate cultivars tend to have a distinct optimum density for grain yield, but indeterminate varieties do not.
Recent work by Board (2000), summarized in Table 2.2,
demonstrates that even determinate cultivars may lack a distinct optimum planting density. His work shows that planting density effects over a wide range of densities (8 to 39 plants m-2) can be eliminated when using determinate cultivars that partition a high proportion of their dry matter into the branches.
TABLE 2.2:
Effect of planting density on the grain yields and yields
components of soya beans after Board (2000)
Planting density
Seed yield
Number of seeds m-
(no plants m-2)
(g m-2)
2
Number of seeds pod-1
Number of pods m-2
8.0
406.6
2459
1.84
1336
14.5
415.3
2505
1.81
1384
39.0
396.1
2386
1.82
1311
Mean
406.0
2450
1.82
1344
12
2.3 Effect of soil water availability on the growth and yield of soya beans
Research into the effects of water stress on soya beans shows the crop to be fairly drought resistant, but not insensitive to water deficits (Korte, Williams, Specht & Sorensen, 1983a and 1983b; Smiciklas, Mullen, Carlson & Knapp, 1992; Batchelor, 1998; Paz, Batchelor & Seidl, 2000).
Soya beans germinate best when planted in moist soil. Irrigation or rain after planting reduces the final plant population, primarily because of soil crusting. Excessively high water contents in the surface layer of the soil also have a negative effect on germination rate (Smit, 2000:8).
Generally, soya bean seed yield is least sensitive to water stress during the vegetative stages.
Insufficient soil water availability during vegetative growth limits crop
growth and may have a negative effect on grain yield.
Adequate soil water
availability during the V stages of growth results in optimum vegetative growth of the soya bean plant, but this does not always result in grain yields that are higher than those obtained under conditions where soil water was less available (Stanley, Kaspar & Taylor, 1980; Smit, 2000:54-55).
Soya beans are most sensitive to water stress during flowering, pod set, and particularly during pod fill (Constable & Hearn, 1980). The important effects of water stress on the growth and yield of soya beans during the different reproductive stages of growth are shown in Table 2.3. When soya beans are subjected to water
13
stress during the early reproductive stages (R1, R2 and R3) LAI is reduced and flower and pod abortion is increased. This, in turn, brings about a reduction in seed number. However, when soil water availability improves during subsequent R stages, an increase in seed mass relative to that obtained from soya beans that was not subjected to water stress during the R1 to R3 stages is likely (Carter & Hopper as cited by Essa, 1979:14; Korte et al., 1983b; Eck, Mathers & Musick, 1987; Smiciklas et al., 1992). Eck, Mathers and Musick (1987), Smiciklas et al. (1992) and Smit (2000:55) report that grain yield in soya beans is most affected by a lack of water when water stress occurs during the R4 to R5 stages.
TABLE 2.3: Effects of soil water availability on growth and yield of soya beans during the different reproductive (R) stages of growth after Ritchie et al. (1994)
Effect of water deficit
Stage R1
Water stress results in flower abortion.
R2
Water stress results in flower abortion.
R3
Water stress results in abortion of young pods. Stress from R1 to R3 does not reduce yields greatly because new flowers and pods can still be produced to compensate for those that were aborted.
R4
Water stress results in a reduction of the number of pods per plant. This is the beginning of a critical period, because flowering nears completion. New pods and seeds are prone to abortion.
R5
Water stress reduces seed size and mass. This is still part of the critical stage, because yield can be reduced by up to 75 percent.
R6
Water stress reduces pods per plant, seeds per pod and seed size.
R7
Water stress at this stage has little effect on yield, because the seeds have already accumulated a sizable portion of their mature dry weight.
R8
Water stress no longer has an effect on grain yield.
14
2.4 Planting density and soil water availability interaction effects on the growth and yield of soya beans
Research investigating the interactions between water and planting density in soya beans shows that optimum planting density increases as soil water availability improves (Taylor, 1980; Graterol, Elmore & Eisenhauer, 1996; Elmore, 1998). As a result, research aimed at determining optimum planting density in soya beans needs to take soil water availability into account. Elmore (1998) reports an optimum planting density of 11 plants m-2 under dryland conditions and 35 plants m-2 under irrigated conditions (Figure 2.1).
-2
Grain yield (g m )
600
400
rainfed
200
irrigation
0 11
35
59
82
-2
Plants per m
FIGURE 2.1: Effect of planting density and soil water availability on the grain yield of soya beans after Elmore (1998)
Taylor (1980) tested the hypothesis that wide-row soya beans yield as much, or more, than narrow-row soya beans during years of low seasonal water supply. When water
15
supply was high, narrow-row soya beans yielded more than wide-row plantings. During years with low seasonal water supply, differences in yield among the row spacing treatments were not statistically significant, even though plants growing in wide rows had larger leaf areas and set more pods than those growing in narrow rows.
Alessi and Power (1982) re-examined Taylor’s hypothesis by broadening the soil water availability spectrum. Over a period of four seasons, narrowly spaced soya beans had the lowest water use efficiency in three of the four years. Compared to widely spaced soya beans, planting the crop in narrow rows increased water use early in the season and left less water available for pod fill. However, Alessi and Power (1982) pointed out that planting density and row spacing had little effect on the grain yield of soya beans under conditions of modest water stress.
2.5 Southern African perspectives on planting density and soil water availability effects in soya beans
According to De Beer (2002) and Smit (2000:5; 2003) South African farmers commonly use a planting density of 30 plants m-2 when growing soya beans under rainfed conditions.
Grain yields obtained under these conditions typically vary
between 1 and 2 tons ha-1. Irrigated soya beans in South Africa typically produce a grain yield of about 3 tons of grain ha-1 (Smit, 2000:5; De Beer, 2002). Smit (2003) recommends that a planting density of 40 plants m-2 be used when growing the crop under irrigated conditions. Results reported by Seed Co. (SA) in Zimbabwe, shown in Table 2.4, tend to support this recommendation. However the yield response to increases in planting density from 16 to 40 plants m-2 was limited.
16
TABLE 2.4: Effect of planting density on soya beans grain yield (after Seed Co., SA)
Planting density (plants m-2)
Grain yield (g m-2)
8
305.0
16
332.0
24
339.0
32
342.0
40
348.0
Mean
333.2
2.6 Conclusions
Despite the substantial increase in local soya bean production over the past three to four decades, production of soya beans in South Africa still does not meet the local demand for the crop. Tailoring planting density to suit the expected level of soil water availability is one of the ways in which local soya bean production can be improved. Generally, grain yield of soya beans increases as planting density is raised until an optimum is reached. In terms of grain yield, the optimum planting density in soya beans increases as growing conditions improve, mainly as a result of an increase in the number of pods being produced per unit area. Soil water availability is one of the important factors determining growing conditions.
However, several factors
affect the relationship between soil water availability and planting density in soya beans. Among these are the ability of soya bean plants to adapt their growth and development to the space that is available, the ability of the crop to recover from
17
water stress, especially when stress occurs during the vegetative stages, and differences among cultivars in terms of the way the crop responds to intra-specific competition or the lack there of.
Generally, research results indicate that the
agronomic practice of optimizing planting density in soya beans to suit the prevailing growing conditions can bring about improvements in grain yield of the order of 5 % to 15 % (Duncan, 1986; Ethredge, Ashley & Woodruff, 1989; Board, Kamal & Harville, 1992; Egli, 1994).
18
CHAPTER THREE
3 MATERIAL AND METHODS 3.1 Introduction
A factorial experiment was conducted with the objective of investigating the interaction of planting density and soil water availability on the grain yield of soya beans. The hypothesis of the study was that there is a positive relationship between planting density and soil water content and grain yield.
The experiment was
conducted during the summer of 2002/03 and repeated during the summer of 2003/04.
3.2 Description of the study site
The field experiment was conducted at the Research Farm of the Tshwane University of Technology (TUT). The Farm is located at Honingnestkranz, near Bon Accord, north of the City of Pretoria, and forms part of the City of Tshwane in the Gauteng Province of South Africa. The Farm is situated at an altitude of 1173 m above sea level and its approximate coordinates are 250 37' S and 280 12' E. Maps showing the location of the TUT Research Farm are presented in Figures 3.1 to 3.4.
19
LIMPOPO
FIGURE 3.1: Map of South Africa showing the location of Gauteng Province
20
City of Tshwane
GAUTENG
FIGURE 3.2: Map of Gauteng Province showing the location of the City of Tshwane
21
City of Tshwane
Honingnestkranz
FIGURE 3.3: Map of the City of Tshwane showing the location of Honingnestkranz
22
Honingnestkranz TUT Research Farm
FIGURE 3.4: Map of Honingnestkranz showing the location of the TUT Research Farm
The Roodeplaat Agricultural Research Station is the weather station that is most representative of the climatic conditions experienced at the TUT Research Farm. It is located approximately 30 km north-east of the TUT Research Farm. The weather station at Bon Accord is located closer to the TUT Research Farm than the Roodeplaat Agricultural Research Station, but Bon Accord only records rainfall. The TUT Research Farm is situated between Bon Accord and the Roodeplaat Agricultural Research Station and all three sites form part of the same climatic zone (ARC-ISCW, 2007). This is borne out, for example, by the mean annual rainfall statistics, which are 648 mm annum-1 at Bon Accord and 641 mm annum-1 at the Roodeplaat Agricultural Research Station.
23
The Roodeplaat Agricultural Research Station is situated at an altitude of 1247 m, a latitude of 250 59’ S and a longitude of 280 36’ E. Important variables describing the climate at the Roodeplaat Agricultural Research Station are summarised in Table 3.1.
TABLE 3.1: Summary of climatic variables recorded at the Roodeplaat Agricultural Research Station over a period of 45 years (after ARC-ISCW, 2005)
Month
Rainfall
Mean
Mean
Mean
Mean
Sunshine
Wind
(mm)
daily
daily
daily
no of
hours
speed
Tmax 0
January
117.1
Tmin 0
Tmean 0
frost
( C)
( C)
( C)
days
29.6
16.8
23.1
0.0
-1
(hr day )
-1
(km day )
Monthly
Eto
Class-A pan
(mm day-1)
evaporation. (mm)
8.6
96.6
238.1
4.9
February
85.4
29.1
16.5
22.8
0.0
8.4
92.6
202.1
4.5
March
71.9
28.1
14.6
21.4
0.0
8.0
85.8
193.3
3.9
April
44.9
25.6
10.7
18.1
0.0
8.2
84.5
150.7
3.0
May
16.9
23.1
5.8
14.5
0.9
8.9
84.0
129.9
2.2
June
6.7
20.5
2.3
11.4
5.9
8.8
85.6
110.5
1.8
July
3.0
20.8
2.0
11.4
6.5
9.1
89.0
141.5
1.9
August
5.4
23.5
4.4
14.0
2.4
9.3
100.0
170.1
2.7
17.8
26.9
8.9
17.9
0.2
9.2
109.0
219.8
3.6
September October
66.8
28.2
12.8
20.5
0.0
8.7
118.4
246.4
4.4
November
102.3
28.2
14.7
21.4
0.0
8.3
114.2
232.8
4.7
December
102.8
28.8
16.0
22.4
0.0
8.4
106.0
244.3
4.9
Total
641.0
2297.5
At the Roodeplaat Agricultural Research Station, most of the rain (591 mm or 92 % of the annual total) falls during the period October to April. Three-quarter of the total annual rainfall (480 mm) occurs during the five-month period November to March inclusive, and this coincides with the growing season of most summer crops, including soya beans.
The mean daily minimum (Tmin) and maximum (Tmax)
temperatures during this five-month period range between 15 0C and 30 0C, which is considered suitable for the production of soya beans (Farias, 1994; Smit, 2000:16). Mean total reference crop evapotranspiration for the five-month period from 24
November to March inclusive, calculated by means of the Penman-Monteith method (ARC-ISCW, 2005), amounts to 692 mm. The mean total class-A pan evaporation for the five-month period November to March inclusive amounts to 1111 mm. Assuming a planting date of 1 November and a growing season that lasts 140 days, and using the crop factors published by Green (1985:33), which are based on American Class A pan evaporation (Green, 1985:6, 33), total evapotranspiration (mm) of soya beans growing at Roodeplaat, was estimated to be 715 mm.
Estimates of mean daily
evapotranspiration by soya beans during the growing season at Roodeplaat are presented in Figure 3.5.
Daily evapotranpiration (mm)
8 7 6 5 4 3 2 1 0 1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
Weeks after planting
FIGURE 3.5: Estimated mean daily evapotranspiration (mm) of soya beans planted on 1 November at Roodeplaat using the procedures of Green (1985)
The estimates presented in Figure 3.5 indicate that evapotranspiration of soya beans planted on 1 November at Roodeplaat peaks during weeks 11 to 13, attaining a value of 7.13 mm day-1 or about 50 mm week-1.
25
The land at the experimental site was nearly flat, sloping gently in a southern direction with a gradient of 1%. The soil at the site was classified as being of the Hutton form and Ventersdorp family (Soil Classification Working Group, 1991:138139). Generally, the texture of the soil was clayey, changing from sandy clay in the A horizon to clay in the B2 horizon and clay loam in the C horizon. The soil was about 2 m deep and moderately well drained. The dry bulk density of the soil was 1 581 kg m-3 in the top 200 mm of the A horizon and declined with soil depth to 1 486 kg m-3 in the B horizon and 1 440 kg m-3 in the C horizon. Following long periods of dry weather the topsoil developed surface cracks typical of soils with vertic properties, but no evidence of slickensides was found in the soil profile. A complete description of the soil profile is presented in Appendix Table A1 and the analytical data appear in Appendix Table A2.
The field capacity was determined using the procedure described by Hensley and de Jager (1982:44) and Boedt and Laker (1985:20). This involved the construction of an earthen ridge around a 3 m x 3 m plot, followed by ponding the soil to thoroughly wet the profile. Once all the water had infiltrated the soil surface was covered with a black plastic sheet to prevent evaporation of water from the surface. Field capacity of the rooting depth of the soil, which was 1030 mm, was determined gravimetrically after allowing for 72 hrs of drainage as recommended by Boedt & Laker (1985:20). Gravimetric sampling to determine the water content of the rooting depth at field capacity was done at six different positions in the plot. The field capacity values that were obtained ranged between 324 mm and 339 mm and the average value was 336 mm. The profile available water capacity (PAWC) of the rooting depth was estimated using two different models. A PAWC value of 118 mm was obtained when using the
26
model developed by Laker (1982: 157) and a value of 94 mm when using the model of Boedt and Laker (1985: 313).
3.3 Experimental procedures
3.3.1 General procedures
In both seasons the experiment employed a split plot design (Little & Hills, 1978:87100) using level of water as main plots and planting density as splits. The experiment involved three levels of water and five planting densities. Treatments were replicated three times. A separate set of plots was used to monitor plant growth by means of destructive sampling.
In both seasons, the upper 1030 mm of the soil profile in the high (HW) and intermediate (IW) water treatments was raised to field capacity three days before planting. Once the plants had emerged, these two treatments received water every week. Irrigation scheduling aimed at supplying the HW-treatment with at least 50 mm water per week, either from rainfall, irrigation or both, and the IW-treatment with at least 25 mm, being half the amount supplied to the HW treatment. The decision to supply at least 50 mm water per week to the HW-treatment was made to ensure that the crop demand for water was met at all times. Since peak demand was estimated to amount to 50 mm per week (Figure 3.5), this amount was supplied to the HWtreatment on a weekly basis from about four weeks after planting until the crop approached physiological maturity. Limiting soil water extraction to a maximum of 50 mm per cycle was deemed adequate to prevent soil water availability from being a
27
limiting factor in crop growth in the HW-treatment, because this amount represented about half of the PAWC of the rooting depth. The implication of the irrigation scheduling practice applied in the HW-treatment was that during both the early and the late parts of the growing season the supply of water to the HW-treatment probably exceeded water use by the crop, but since the soil was deep and moderately well drained, it was assumed that excess water would be removed from the rooting zone by deep percolation without having a negative effect on the development of the crop. The low water treatment (LW) consisted of planting in soil that had not been raised to field capacity. Following establishment, which involved several light irrigations, because conditions during emergence were dry, especially during the 2003/04 season, the crop was left to subsist on rainfall and stored soil water.
Irrigation was applied by means of a hosepipe to which a water meter with accuracy of 1 litre was attached (Figure 3.6). During the growing season rainfall was measured daily using a plastic rain gauge that was positioned on the edge of the experimental site at a height of 1.20 m above the soil surface.
28
FIGURE 3.6: A water meter with accuracy of 1 litre was used to measure the amount of irrigation water applied to the plots
The profile water content of the upper 1030 mm of the soil profile was determined at the time of planting and again when the crop had reached physiological maturity. This enabled the estimation of the net contribution of stored soil water to total consumptive water use in the three water treatments, but water lost through deep percolation could not be accounted for.
Soil water samples were taken
gravimetrically at depth intervals of 200 mm by means of a soil auger. Dry soil bulk density was determined for each depth interval enabling the conversion of gravimetric water content to volumetric water content.
In the 2002/03, experiment the soil profile water content at planting was determined only in six of the plots in which the soil was raised to field capacity (IW and HW treatments) and three of the plots that received no pre-plant irrigation (LW treatment).
29
The mean of the six profile water contents of the plots that were charged before planting was used to represent the profile water content in all the plots of the HW and IW treatments and the mean of the three soil water contents in the plots that did not receive pre-plant irrigation was used to represent the profile water content in all the plots of the LW treatment. At physiological maturity the profile water content was determined in all 45 plots separately.
In the 2003/04 experiment, profile water
content was determined in each plot individually both at planting and at physiological maturity.
Estimates of the consumptive water use by soya beans in the different water treatments, inclusive of any water that was lost through deep percolation, were the sum of rainfall and irrigation water received during the growing season and the net contribution of stored water in the upper 1030 mm of the soil profile.
Total
consumptive water use data for the 2003/04 season were analysed statistically, because all the necessary measurements were made in each plot individually. As indicated, in the 2002/03 experiment the profile water content at planting was not determined for each plot separately, and for this reason the consumptive water use data obtained in that experiment were not analysed statistically.
Five planting densities were established. Square planting was employed and plant spacing ranged from 45 cm x 45 cm to 11 cm x 11 cm, generating planting densities that ranged between 5 plants m-2 and 80 plants m-2 (Table 3.2).
30
TABLE 3.2: Plant spacing and planting densities used in the 2002/03 and 2003/04 soya bean experiments
Spacing (cm)
Equivalent planting density (plants m-2)
45 x 45
5
32 x 32
10
22 x 22
20
16 x 16
40
11 x 11
80
3.3.2 Specific procedures that applied to the 2002/03 experiment
The 2002/03 experiment was conducted on land that was previously planted to Teff grass (Eragrostis tef). Soil preparation started by incorporating the sod and stover of the previous crop using a disc-plough, and was followed by seedbed preparation using an S-tine implement with a rotocart. The plots assigned to the HW and IW treatments were converted to level basins using spades and rakes. Levelling occurred during successive irrigations aimed at charging the soils in these plots to field capacity. A view of these level basins is presented in Figure 3.7.
31
FIGURE 3.7: View of the level basins used to maintain the high water (HW) and intermediate water (IW) treatment
The gross plot size was 5 m x 5 m = 25 m2. The net plots obtained by removing the guard rows ranged in size from 24.56 m2 to 24.89 m2 depending on the spacing of the treatment.
Samples of the topsoil (0 - 20 cm) were taken in each plot a week before planting and again on the day after harvesting. In each case the samples from the different plots were bulked and homogenised before taking a single composite sample for analysis, which was conducted by the ARC-Institute for Soil, Climate and Water.
Selected chemical
properties of the topsoil before planting and after harvesting the experiment are presented in Table 3.3.
32
TABLE 3.3: Chemical properties of the topsoil at the site of the 2002/03 experiment before the experiment was planted and after it was harvested
Time of
Total N
K
Ca
Mg
Na
sampling
S-
pHwater
P
value (%)
Before planting
0.094
After harvest
0.099
--------------------(cmol(+) kg-1)---------------------1.35 9.65 4.32 0.21 15.83 1.39
9.56
4.22
0.29
15.43
(mg kg-1) 6.94
93
6.95
109
At the time of planting, the results of the soil analysis were not yet available. The Tshwane Nutrition Project, which provided the funding for the conduct of the experiment, prescribed an organic approach to plant production. For this reason, it was decided to apply Promis, which is a composted breeding litter certified organic by ECOCERT S.A. and supplied by National Plant Foods CC in Rustenburg. On average, Promis contains 4 % N, 1.5 % P, 1.5 % K and 3 % Ca by mass (Hogen, 2002). Promis was applied broadcast at a rate of 5 tons ha-1 (12.6 kg per plot), and worked into the surface soil (top 150 mm) using spades. The application rate used was aimed at meeting the phosphorus requirements of a soya bean crop that produced a grain yield of 4.5 t ha-1. The choice of this particular target yield was based on the results of the national soya bean cultivar trial conducted during 2001/02 on the TUT Research Farm (De Beer & Pretorius, 2002), in which grain yields of 4.5 tons ha-1 were achieved. To achieve a grain yield of 4.5 t ha-1, the FSSA (1999:187) recommends the application of 60 kg P ha-1 on soils that are low in P ( F
Model
20
370464.6258
18523.2313
28.27
< 0.0001
Error
24
15724.9040
655.2043
Corrected total
44
386189.5298
R-square
Coefficient of variation
Root MSE
Yield g m-2 Mean
0.959282
8.175388
25.59696
313.0978
Source
DF
Type I SS
Mean square
F value
Pr > F
Water
2
1054.6991
527.3496
0.80
0.4589
Density
4
363790.7231
909476808
138.81
< 0.0001
Block
2
148.9231
74.4616
0.11
0.8931
Water*Block
4
2811.2996
702.8249
1.07
0.3918
Water*Density
8
2658.9809
332.3726
0.51
0.8389
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
1054.699111
527.349556
0.75
0.5288
102
TABLE C2: Analysis of variance for number of soya bean pods plant-1, 2002/03 experiment
Source
DF
Sum of square
Mean square
F value
Pr > F
Model
20
220988.9333
11049.4467
22.32
< 0.0001
Error
24
11880.2667
495.0111
Corrected total
44
232869.2000
R-square
Coefficient of variation
Root MSE
Pods plant-1 Mean
0.948983
18.66514
22.24885
119.2000
Source
DF
Type I SS
Mean square
F value
Pr > F
Water
2
3910.5333
1955.2667
3.95
0.0329
Density
4
212798.9778
53199.7444
107.47
< 0.0001
Block
2
370.5333
185.2667
0.37
0.6917
Water*Block
4
1400.5333
350.1333
0.71
0.5948
Water*Density
8
2508.3556
313.5444
0.63
0.7420
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
3910.533333
1955.266667
5.58
0.0695
TABLE C3: Analysis of variance for number of soya bean pods m-2, 2002/03 experiment
Source
DF
Sum of square
Mean square
F value
Pr > F
Model
20
44738411.03
2236920.55
16.64
< 0.0001
Error
24
3226439.31
134434.97
Corrected total
44
47964850.34
R-square
Coefficient of variation
Root MSE
Pods m -2 Mean
0.932733
16.98557
366.6537
2158.619
Source
DF
Type I SS
Mean square
F value
Pr > F
Water
2
1129579.26
564789.63
4.20
0.0273
Density
4
42024393.02
10506098.26
78.15
< 0.0001
Block
2
116625.93
58312.96
0.43
0.6530
Water*Block
4
241104.15
60276.04
0.45
0.7725
Water*Density
8
1226708.67
153338.58
1.14
0.3732
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
1129579.261
564789.630
9.37
0.0309
103
TABLE C4: Analysis of variance for number of soya bean seeds plant-1, 2002/03 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
1056429.244
52821.462
19.62
< 0.0001
Error
24
64627.333
2692.806
Corrected total
44
1121056.578
R-square
Coefficient of variation
Root MSE
Seeds plant-1 Mean
0.942351
20.33572
51.89225
255.1778
Source
DF
Type I SS
Mean square
F value
Pr > F
Water
2
22314.444
11157.222
4.14
0.0285
Density
4
1012132.356
253033.089
93.97
F
Water
2
22314.44444
11157..22222
7.10
0.0483
TABLE C5: Analysis of variance for number of soya bean seed m-2, 2002/03 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
187030598.0
9351529.9
12.47
< 0.0001
Error
24
17997240.9
749885.0
Corrected total
44
205027838.9
R-square
Coefficient of variation
Root MSE
Seeds m-2 Mean
0.912221
18.94802
865.9590
4570.181
Source
DF
Type I SS
Mean square
F value
Pr > F
Water
2
5943450.1
2971725.0
3.96
0.0326
Density
4
175217599.7
43804399.9
58.41
< 0.0001
Block
2
640172.4
320086.2
0.43
0.6574
Water*Block
4
1017300.3
254325.1
0.34
0.8488
Water*Density
8
4212075.5
526509.4
0.70
0.6867
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
5943450.090
2971725.045
11.68
0.0214
104
TABLE C6: Analysis of variance for number of soya bean seeds pod-1, 2002/03 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
0.53777778
0.02688889
3.14
0.0042
Error
24
0.20533333
0.0085555.6
Corrected total
44
0.74311111
R-square
Coefficient of variation
Root MSE
Seed pod-1 Mean
0.723684
4.273441
0.092496
2.164444
Source
DF
Type I SS
Mean square
F value
Pr > F
Water
2
0.00577778
0.00288889
0.34
0.7168
Density
4
0.16755556
0.04188889
4.90
0.0050
Block
2
0.22711111
0.11355556
13.97
0.0001
Water*Block
4
0.03422222
0.00855556
1.00
0.4269
Water*Density
8
0.10311111
0.01288889
1.51
0.2070
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
0.00577778
0.00288889
0.34
0.7320
TABLE C7: Analysis of variance for 100 seed mass of soya bean, 2002/03 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
6695.14044
334.75702
1.50
0.1720
Error
24
5368.66267
223.69428
Corrected total
44
12063.80311
R-square
Coefficient of variation
Root MSE
100 seeds mass Mean
0.554978
9.485562
14.95641
157.6756
Source
DF
Type I SS
Mean square
F value
Pr > F
Water
2
1355.328444
677.664222
3.03
0.0671
Density
4
1272.280889
318.070222
1.42
0.2570
Block
2
425.659111
212.829556
0.95
0.4003
Water*Block
4
1358.451556
339.612889
1.52
0.2285
Water*Density
8
2283.420444
285.427556
1.28
0.3015
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
1355.328444
677.664222
2.00
0.2506
105
TABLE C8: Analysis of variance for consumptive water use of soya bean, 2003/04 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
8
36893.4
4611.7
22.86
< 0.001
Error
24
4841.8
201.7
Corrected total
44
1338027
R-square
Coefficient of variation
Root MSE
Yield g m -2 Mean
0.931312
10.84198
50.50056
465.7871
Source
DF
Type III SS
Mean square
F value
Pr > F
Block
2
1431.9
716.0
1.56
Water*Block
4
1831.4
457.9
2.27
Water
2
1107761.8
553880.9
1209.73
< 0.001
Density
4
185267.1
46316.8
229.58
< 0.001
Water*Density
8
36893.4
4611.7
22.86
< 0.001
TABLE C9: Analysis of variance for grain yield of soya bean, 2003/04 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
829881.7027
417494.0851
16.27
< 0.0001
Error
24
61207.3525
2550.3064
Corrected total
44
891089.0551
R-square
Coefficient of variation
Root MSE
Yield g m -2 Mean
0.931312
10.84198
50.50056
465.7871
Source
DF
Type III SS
Mean square
F value
Pr > F
Block
2
8251.5301
4125.7650
1.62
0.2192
Water*Block
4
57463.7289
14365.9322
2.63
0.0024
Water
2
143988.2195
71994.1098
28.23
< 0.0001
Density
4
588902.0947
147225.5237
57.73
< 0.0001
Water*Density
8
31276.1295
39039.5162
1.53
0.1981
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
143988.2195
71994.1098
5.01
0.0814
106
TABLE C10: Analysis of variance for number of soya bean pods plant-1, 2003/04 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
87641.64444
4382.08222
33.75
< 0.0001
Error
24
3116.00000
129.83333
Corrected total
44
90757.64444
R-square
Coefficient of variation
Root MSE
Pods plant-1 Mean
0.965667
12.50915
11.39444
91.08889
Source
DF
Type III SS
Mean square
F value
Pr > F
Block
2
863.51111
431.75556
3.33
0.0531
Water*Block
4
391.82222
97.95556
0.75
0.5649
Water
2
1876.31111
938.15556
7.23
0.0035
Density
4
79592.75556
19898.18889
153.26
< 0.0001
Water*Density
8
4917.24444
614.65556
4.73
0.0014
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
1876.31111
938.15556
9.58
0.0298
TABLE C11: Analysis of variance for number of soya bean pods m-2, 2003/04 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
24752252.00
1237612.60
15.18
< 0.0001
Error
24
1956632.00
81526.33
Corrected total
44
267088884.00
R-square
Coefficient of variation
Root MSE
Pods m-2 Mean
0.926742
16.42540
285.5282
1738.333
Source
DF
Type III SS
Mean square
F value
Pr > F
Block
2
170497.60
85248.80
1.05
0.3669
Water*Block
4
384633.07
96158.27
1.18
0.03449
Water
2
233030.93
116515.47
1.43
0.2592
Density
4
23670368.89
5917592.22
72.59
< 0.0001
Water*Density
8
293721.51
36715.19
0.45
0.8782
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
233030.9333
116515.4667
1.21
0.3878
107
TABLE C12: Analysis of variance for number of soya bean seeds plant-1, 2003/04 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
389180.4444
19459.0222
26.17
< 0.0001
Error
24
17847.8667
743.6611
Corrected total
44
407028.3111
R-square
Coefficient of variation
Root MSE
Seeds plant-1 Mean
0.956151
14.56393
27.27015
187.2444
Source
DF
Type III SS
Mean square
F value
Pr > F
Block
2
4608.5778
2304.2889
3.10
0.0635
Water*Block
4
2694.8889
673.7222
0.91
0.4762
Water
2
6730.8444
3365.4222
4.53
0.0215
Density
4
34.9526.9778
87381.7444
117.50
< 0.0001
Water*Density
8
25619.1556
3202.3944
4.31
0.0025
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
6730.844444
3365.422222
5.00
0.0817
TABLE C13: Analysis of variance for number of soya bean seeds m2, 2003/04 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
90294262.7
4514713.1
10.53
< 0.0001
Error
24
10286223.1
428592.6
Corrected total
44
100580485.8
R-square
Coefficient of variation
Root MSE
Seeds m-2 Mean
0.897731
18.66870
654.6699
3506.778
Source
DF
Type III SS
Mean square
F value
Pr > F
Block
2
98155.38
49077.69
0.11
0.8923
Water*Block
4
2724495.56
681123.89
1.59
0.2095
Water
2
779113.64
389556.82
0.91
0.4164
Density
4
84866156.22
21216539.06
49.50
< 0.0001
Water*Density
8
1826341.91
228292.74
0.53
0.8202
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
779113.6444
389556.8222
0.57
0.6047
108
TABLE C14: Analysis of variance for number of soya bean seeds pod-1, 2003/04 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
0.63184551
0.03159228
1.22
0.3193
Error
24
0.62243680
0.02593487
Corrected total
44
1.25428231
R-square
Coefficient of variation
Root MSE
Seed pod-1 Mean
0.503751
7.793998
0.161043
2.066244
Source
DF
Type III SS
Mean square
F value
Pr > F
Block
2
0.09160551
0.04580276
1.77
0.1925
Water*Block
4
0.08222102
0.02055526
0.79
0.5416
Water
2
0.09603258
0.04801629
1.85
0.1787
Density
4
0.29320520
0.07330130
2.83
0.0472
Water*Density
8
0.06878120
0.00859765
0.33
0.9453
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
0.09603258
0.04801629
2.34
0.2128
TABLE C15: Analysis of variance for seed mass (100 seeds), 2003/04 experiment
Source
DF
Sum of squares
Mean squares
F value
Pr > F
Model
20
21488.40000
1074.42000
3.51
0.0020
Error
24
7348.80000
306.20000
Corrected total
44
28837.20000
R-square
Coefficient of variation
Root MSE
100 seed mass Mean
0.745162
7.726776
1749857
226.4667
Source
DF
Type III SS
Mean square
F value
Pr > F
Block
2
1216.93333
608.46667
1.99
0.1590
Water*Block
4
1934.26667
483.56667
1.58
0.2120
Water
2
1106.80000
553.40000
1.81
0.1857
Density
4
15116.75556
3779.18889
12.34
< 0.0001
Water*Density
8
2113.64444
264.20556
0.86
0.5599
Source
DF
Type III SS
Mean square
F value
Pr > F
Water
2
1106.800000
553.400000
1.14
0.4046
109
