DRYLAND CROPPING SYSTEMS

Published May, 2002

DRYLAND CROPPING SYSTEMS Establishment of Wheat Seedlings after Early Sowing and Germination in an Arid Mediterranean Environment Joshua D. Klein, Israel Mufradi, Shlomo Cohen, Yonit Hebbe, Silvia Asido, Bella Dolgin, and David J. Bonfil* ABSTRACT

use efficiency and wheat grain yield under dryland conditions (Bonfil et al., 1999). Also, clean fallow generally increased soil water storage (Bonfil et al., 1999). No-tillage management has also been used for barley (Hordeum vulgare L.), watermelon (Citrullus vulgaris Schrad.), pea (Pisum sativum L.), and sunflower (Helianthus annuus L.) because it facilitates both annual cropping and crop rotation in dry regions where monoculture and fallow fields are otherwise the norm (Bonfil, unpublished data, 2000; Lo´pez-Bellido et al., 1996). In addition to field management techniques, chemical or hormonal treatments can be used to help wheat survive temporary drought. Applying monopotassium phosphate (KH2PO4 ) at anthesis delayed wheat senescence in arid regions of Morocco and China (Benbella and Paulsen, 1998). Gibberellin (GA) synthesis inhibitors chlorocoline chloride [2-chloroethyltrimethylammonium chloride] (CCC), triazoles such as paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2, 4-triazol-l-yl)pentan-3-ol] (PP333), and acylcyclohexanediones such as trinexapac-ethyl [ethyl 4-cyclopropyl(hydroxy)methylene-3,5-dioxocyclohexanecarboxylate] (TE) may also protect grain crops under environmental stress conditions (Halmann, 1990; Rademacher, 2000; Zhang and Schmidt, 2000). Chlorocoline chloride blocks GA formation by blocking cyclization of geranylgeranyl pyrophospate to copalyl pyrophosphate while triazoles operate further down the GA synthesis pathway by inhibiting oxidation of ent-kaurene to kaurenoic acid. Trinexapac-ethyl inhibits GA synthesis by blocking the transformation of GA20 to GA1 (Rademacher, 2000). The objectives of the present study were to identify optimal crop management practices for wheat seedling survival and maintenance of crop yield in dryland farming areas where one instance of germination-inducing precipitation could occur before the true beginning of the rainy season. We also investigated the use of plant growth regulators (PGRs) to enhance seedling survival under severe drought conditions.

Seedling establishment of dryland crops in semiarid and arid zones is limited by precipitation. Spring wheat (Triticum aestivum L. emend. Thell.) generally is sown in dry soil in the dryland regions of Israel before the rainy season starts. We compared the effects of no-tillage, conventional tillage, and plant growth regulators on wheat seedling growth to identify the optimal crop management system for seedling establishment in dryland farming. Experiments were conducted during 1998 and 1999 at the Gilat Experimental Station located in southern Israel (annual precipitation of 222 and 72 mm for 1998 and 1999, respectively; soil type is sandy loam loess—Torrifluvents). Neither inhibitors of gibberellin synthesis (chlorocoline chloride, paclobutrazol, and trinexapac-ethyl) nor monopotassium phosphate (KH2PO4 ) enhanced seedling survival under drought stress when sprayed on seedlings at the two-leaf stage. No-tillage led to increases in water content in the upper (0–30 cm) soil layer and in seedling water content and seedling biomass. No-tillage management also maintained seedling viability compared with the control, with seedlings surviving as long as 35 d without precipitation. No-tillage management allows successful seedling establishment and growth after a dry period that follows germination.

W

heat is the crop grown on most of the dryland areas in Israel, covering more than 80 000 ha of arable dry land. Sowing generally is done in November at the beginning of the rainy season. Mahdi et al. (1998) showed that the maximal establishment and yield of wheat in a semiarid Mediterranean environment after early sowing was achieved when seeds were sown to a 6-cm depth during mid-November, after the soil was already moist. Israeli farmers usually do not wait for the soil to be wet before sowing, and in absence of early rain, most fields are therefore sown in dry soil. However, it is very common in this region for a dry period of 3 to 5 wk to occur after the initial rain. If the first rains provide sufficient moisture for germination, then the seedlings grow under dry conditions combined with a limited water supply. In some cases, the seedlings die, and farmers have to sow the field once again. No-tillage (NT) management increased both water

MATERIALS AND METHODS

J.D. Klein, Agric. Res. Organ., Dep. of Field Crops and Nat. Resour., Volcani Cent., POB 6, Bet Dagan, 50250 Israel; I. Mufradi, S. Asido, B. Dolgin, and D.J. Bonfil, Agric. Res. Organ., Dep. of Field Crops and Nat. Resour., Gilat Exp. Stn., M.P. Negev 2, 85280 Israel; and S. Cohen and Y. Hebbe, Inst. for Agric. Res. according to the Torah, Yad Binyamin, 76812 Israel. Contribution 128/2000 from the Agricultural Research Organization, Institute of Field and Garden Crops, Bet Dagan, Israel. Received 23 Apr. 2001. *Corresponding author (bonfil@ netvision.net.il).

The experiments reported here were conducted during the 1997–1998 and 1998–1999 seasons at the Gilat Experiment Station located in southern Israel (31⬚21⬘ N, 34⬚42⬘ E). Soil, climatic characteristics, and crop management of these plots (average annual precipitation of 237 mm; soil type is sandy Abbreviations: CT, conventional tillage; CW, continuous wheat; DW, dry weight; FW, fresh weight; GA, gibberellin; NT, no-tillage; PGR, plant growth regulator; WF, wheat after fallow.

Published in Agron. J. 94:585–593 (2002).

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AGRONOMY JOURNAL, VOL. 94, MAY–JUNE 2002

loam loess—Torrifluvents) have been previously described (Amir et al., 1991; Bonfil et al., 1999). In all experiments, the spring wheat cultivar Nirit (Zeraim Seed Co., Gedera, Israel) was sown with a NT drill (Great Plains), at a rate of 250 seeds m⫺2, using an 18-cm row spacing. Seedbed disturbance with this drill was restricted to the depth of sowing (2–3 cm) and to ⬍1 cm width of furrow. The NT fields were covered by 1500 to 3000 kg ha⫺1 stubble. During the 1997–1998 season, we compared NT management (second year as NT) with conventional tillage (CT) (tandem-disk harrow) management following wheat. Wheat was sown on 23 Sept. 1997 under three water regimes. In two of the regimes, wheat was germinated with 400 m3 ha⫺1 irrigation (equivalent to 40 mm of rain) on 13 Oct. 1997 while in the third, seeds were germinated by a natural rainfall of 30 mm on 18 Oct. 1997. Plants in one of the irrigated plots and in the natural rainfall regime were left to grow without any further supplemental irrigation. This resulted in plots with initial water supplies of 70 and 30 mm, respectively. The third regime received another two irrigations of 30 and 40 mm on 28 Oct. 1997 and 11 Nov. 1997, respectively, for a total of 140 mm, which effectively meant an unlimited water supply for the germinating wheat seedlings. The experiment was laid out in a randomized complete block with a split plot arrangement. Main plots were water regimes, and crop management treatments (CT or NT) were subplots. Each main plot was replicated twice, and each subplot treatment was repeated three times within a main plot. At least 12 m of guard strip separated each main-plot treatment, and experimental units were 2 by 10 m. Field maintenance (fertilizers and herbicides) was in accordance with standard recommendations for the region. Seedling stand was measured 22 d after emergence by counting the seedlings within a 0.3-m2 frame placed randomly within each subplot. Dry matter accumulation, plant water content [calculated from the fresh weight (FW) and dry weight (DW)], plant height, and leaf number were measured weekly using the mean of 10 plants randomly sampled from each experimental unit. Farm advisors from the Ministry of Agriculture evaluated seedling survival in each plot 36 d after emergence. In 1998–1999, wheat was sown on 15 Sept. 1998 under NT (second year under this management) and CT and was germinated with 250 m3 ha⫺1 irrigation (equivalent to 25 mm of rain) on 15 Oct. 1998. One month later, another 250 m3 ha⫺1 was applied. This field was termed Field I. The GA synthesis inhibitors paclobutrazol (500 and 1000 mg L⫺1 ) and Moddus [trinexapac-ethyl, a gift from Novartis Corporation (now Syngenta), Muenchwilen, Switzerland; 0.125 and 0.25% (v/v) a.i.] and the fertilizer monopotassium phosphate (KH2PO4, 10 kg ha⫺1 ) were sprayed at 20 mL m⫺2 2 wk after emergence. Unsprayed plants served as controls. The experiment was laid out in a randomized complete block with a split-plot arrangement with four replicates. Main plots were crop management (CT or NT) and subplots were spray treatments. Each subplot was 2 by 10 m. Field maintenance (fertilizers and herbicides) was in accordance with standard recommendations for the region. A separate field with the same experimental design, sowing date, and management as Field I was established without early initial irrigation and was termed Field II. Wheat seeds in this field were germinated by 20 mm of rain that fell on 17 Jan. 1999. The field was further irrigated (40 mm) late in the season on 12 Apr. 1999. The PGRs applied in the early germinating field were also applied here, with the addition of chlorocoline chloride (500 mg L⫺1 ). As in 1997–1998, means of 10 plants that were sampled

weekly from each experimental unit of Fields I and II were used for determination of dry matter accumulation, plant water content (calculated from the FW and DW), plant height, and leaf number. In a third trial in 1998–1999, we also examined the effect of various crop management systems on wheat seedling survival under drought stress. Wheat was sown after fallow (WF system, 1 crop in 2 yr) or in a continuous wheat (CW) system. The CW and WF rotations had been established since 1975, at the beginning of this long-term fixed experiment, while the NT system was added in 1994 to this experiment. In both cases, NT management was compared with CT management. Seeds were sown on 15 Nov. 1998 and were germinated by 20 mm of rain in January 1999. The experiment was laid out in a randomized complete block design, with four replicate 20- by 10-m plots per treatment. All field management practices, with the exception of the factors being tested, were in accordance with standard recommendations for the region. There was no supplemental irrigation. Plants were sampled in March 1999 from within a 0.3-m2 frame placed randomly in each plot to measure dry matter accumulation, plant water content (calculated from the FW and DW), plant height, and leaf number. A 50-m2 swath was harvested in May 1999 in each plot to determine straw and grain yield. Samples (approx. 150 g) of soil were taken from each of the four management systems at 30-cm increments to a depth of 150 cm at three times: before sowing, after 85% of the annual precipitation had fallen, and after harvest (25 Oct. 1998, 23 Feb. 1999, and 8 June 1999). Available soil water ranged from 7.5 g kg⫺1 (wilting point) to 18 g kg⫺1 (field capacity) for the 0- to 150-cm layers, as measured gravimetrically (drying method, w/w). All data were statistically analyzed by SAS software. Separate analyses were performed for each sampling date. The General Linear Models procedure was used to test effects at the 5% level of probability. Tillage, spray, and rotation were considered as fixed effects, and their means were separated by LSD.

RESULTS Rain conditions during the period of this study differed markedly from the distribution and total average annual precipitation (237 mm). In 1997–1998, an unusually large amount of rain fell during October (Fig. 1A) while during the usual rainy season, precipitation reached only 180 mm between 9 Dec. 1997 and 24 Mar. 1998. A severe drought prevailed during 1998–1999, resulting in only 72 mm of precipitation being available for the wheat (Fig. 1B) plus an additional 40 to 60 mm of irrigation (Fig. 1B) or stored soil water (WF system). As is frequently the case in Israel, no rain fell between April and October. Moreover, the low precipitation was accompanied by high pan evaporation that reached about 260 (1997–1998) or 400 mm (1998–1999) from germination until the first rains arrived (Fig. 1). Hence, both 1997–1998 and 1998–1999 experiments were established under similar stress conditions during the early growth period and could represent seedling survival under drought conditions. In 1997–1998, NT management generally resulted in increased seedling DW under both the 70- and 140-mm regimes compared with CT. Throughout the growing season, there was no difference between NT and CT in

KLEIN ET AL.: WHEAT SEEDLING ESTABLISHMENT IN AN ARID MEDITERRANEAN ENVIRONMENT

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Fig. 1. Annual cumulative rainfall, Class A evaporation, and irrigation from the time of wheat sowing to harvest (no rainfall occurred in the other months) in (A) 1997–1998 and (B) 1998–1999. Field I received supplemental irrigation early in the season; Field II received irrigation only late in the season.

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Fig. 2. Accumulation of aboveground dry matter in wheat grown in 1997–1998 with conventional tillage (CT) or no-tillage (NT) under three levels of water application causing emergence. Values shown are means of 10 plants. (Vertical bars represent LSD at each sampling date.)

seedlings grown with natural rainfall plus 30 mm of irrigation (Fig. 2). No-tillage water regimes generally maintained seedling water content better than CT for the first 29 d after irrigation (Fig. 3). Plots that received 70 or 140 mm precipitation attained emergence of ⬎200

plants m⫺2 (Table 1). However, when only 30 mm of water was applied, emergence under NT was nearly three times that under CT management (Table 1). Moreover, the difference shown in Fig. 2 and 3 between NT and CT could be greater because more seedlings

Fig. 3. Seedling water content of wheat grown in 1997–1998 with conventional tillage (CT) or no-tillage (NT) under three levels of water application causing emergence. Values shown are means of 10 plants. (Vertical bars represent LSD at each sampling date.)

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Table 1. Effect of tillage on wheat seedling emergence and soil water content under three water regimes in 1997–1998. Tillage† and water regime CT and 30 mm CT and 70 mm CT and 140 mm NT and 30 mm NT and 70 mm NT and 140 mm

Plant stand 22 DAE‡

Soil water content§ 22 DAE

seedlings m⫺2 50e¶ 225c 251bc 143d 281ab 317a

% 5.7e 7.0d 12.1b 6.9d 7.7c 13.0a

† CT, conventional tillage; NT, no-tillage. ‡ DAE, days after emergence. § 0–30 cm soil layer, determined by drying method (w/w). ¶ Means within a column followed by the same letter are not significantly different (P ⫽ 0.05) using LSD mean separation procedure.

germinated under NT management (Table 1), and therefore utilized more water. This seedling number increase resulted from better emergence conditions under NT despite the small amount of water available (30 mm). No-tillage plots that exceeded 250 seedlings m⫺2 probably were benefiting from germination and growth of seeds left in the field from the previous year’s harvest, as was clear from their location between sown furrows. All of the seedlings that emerged during late October survived until the next rain, which fell during December. However, those seedlings that did not receive further irrigation (i.e., remained at 30 mm) were exposed to severe drought during tillering and spike development, and their potential yield decreased dramatically. Under criteria of the Israeli Ministry of Agriculture Extension Service, these plots needed to be resown 36 d after germination. Sixty percent of CT plots needed to be resown, and all others needed to be at least partially resown. Only 40% of NT plots needed to be even partially resown, and no NT plot needed to be completely resown. This is further evidence of increased seedling survival under NT management. In the second season (1998–1999), NT management generally led to increased dry matter accumulation (Fig. 4), plant water content (Fig. 5), and plant height (data not shown) compared with CT management. No effect of any PGR was detected (data not shown), so values presented are averaged over all PGR treatments. The decrease in dry matter accumulation that occurred during December under NT (Fig. 4A) could be attributed to concentrated feeding by birds and other organisms on what at the time was the only source of seedlings in the area. During the 4-wk dry period after the initial rain, pan evaporation was six times that of the water that had been applied (Fig. 1B), and seedling water content decreased from 80% to 45 to 55% in both NT and CT (Fig. 5A). The water content of plants that germinated late in winter decreased from 80% in January to 20 to 35% by mid-April, irrespective of cultural management (Fig. 5B). These late-germinating plants were irrigated with 400 m3 ha⫺1 in mid-April to test if they were still alive. Almost 100% of the plants under CT management did not respond to the supplemental water. However, plants in the NT plots became greener and increased their water content from 35 to 48% in response to the late irrigation (Fig. 5B). The severe

Table 2. Effect of tillage and crop rotation on rainfed wheat development and yield production in 1998–1999. Crop rotation–tillage system† WF CT

CW NT

CT

NT

Plant characteristics (March 1999) Dry weight, g/10 plants 4.4bc‡ 9.2a 2.6c 4.9b Water content, % 68.8a 71.3a 59.0c 64.3b Height, cm 27.9b 38.0a 23.4c 31.7b Leaf no. 8.2ab 8.6a 7.2c 8.0b Yield (May 1999) 293b 601a 21c 3c Grain, kg ha⫺1 1040b 1914a 160c 206c Biomass (grain ⫹ straw), g m⫺2 † WF, wheat after fallow; CW, continuous wheat; CT, conventional tillage; NT, no-tillage. ‡ Means within a row followed by the same letter are not significantly different (P ⫽ 0.05) using LSD mean separation procedure.

drought conditions permitted very little heading, despite the plants’ viability; hence, there was no seed yield from this crop. The severe drought also affected wheat seedling survival in the comparison of crop management systems (Table 2). The WF–NT system produced the highest biomass, and WF in general maintained the highest moisture level in the shoot. During vegetative growth, results from the WF–CT plots were similar to those from CW–NT plots while the CW–CT plots had the poorest results for these drought conditions. Although the lowest water content was 59% at this stage, plants with CW management lost water and died without producing much grain. However, under the WF system, which had stored water from the previous year, plants yielded grain even under severe drought, with WF–NT management producing 601 kg ha⫺1. Soil water content under different management systems depended on the previous season’s water use. Soil from the fallow year (WF) retained about 600 m3 water ha⫺1 in the 0- to 120-cm layer (equivalent to 60 mm of rain), and NT plots contained more water than CT plots (Fig. 6A). Despite the drought, there was a connection between the water from the 1999 season rainfall and the stored water in the WF plots (Fig. 6B). The management system employed had little impact on postharvest water content in the 0- to 90-cm layer (Fig. 6C), except for the CW–CT system, which had drier soil. However, there were differences in the deeper soil layers, probably as a result of root penetration. In WF plots, the wheat roots could use the water stored in 90- to 120-cm layer, as shown by a decrease in total soil water content of about 2% (i.e., from ≈10% to ≈8%) in the 60- to 120cm layer under WF management (Fig. 6B and 6C).

DISCUSSION In previous studies, reasonable wheat yields were obtained with only 150 to 170 mm of rainfall (Bonfil et al., 1999; Turner, 1997). However, under severe drought conditions (Bonfil et al., 1999), only WF–NT management produced acceptable grain quality. In the present research, we obtained a reasonable wheat yield under WF with only 60 to 70 mm of rainfall, which when

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Fig. 4. Accumulation of aboveground dry matter in wheat that emerged in (A) October 1998 or (B) January 1999 under conventional tillage (CT) or no-tillage (NT). Columns represent amount of precipitation (rain or irrigation). Values shown are means of four replicates, each consisting of 10 plants. (Vertical bars represent LSD at each sampling date.)

added to the 60-mm equivalent already stored in the soil, meant that even 120 mm of water was sufficient to produce grain. Turner (1997) similarly found that 110 mm of rain was sufficient for a minimal wheat yield. Although wheat grown with 150 mm of water was viable

economically for both grain and hay (Bonfil et al., 1999), the crop of the present experiment (with 120 mm) was more useful commercially for hay or grazing. The absence of a PGR effect on seedling growth and survival could be related to the type and timing of appli-


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Fig. 5. Seedling water content of wheat that emerged in (A) October 1998 or (B) January 1999 under conventional tillage (CT) or no-tillage (NT). Columns represent amount of precipitation (rain or irrigation). Values shown are means of four replicates, each consisting of 10 plants. (Vertical bars represent LSD at each sampling date.)

cation. In normal seasons, the timing of germination is critical for use of available water and, therefore, critical to survival. In such cases, seed treatments that will delay seedling emergence are problematic. However, in the case of early emergence followed by a dry period, seed-

ling treatments could be an option to reduce water use during initial development (Zadoks no. 12–15). Unfortunately, at this stage of development (two to three leaves), the total leaf area is very small, and most of the spray material falls on the soil and is not absorbed

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Fig. 6. Profile of soil water distribution (A) before sowing, (B) after 85% of precipitation, and (C) after harvest as affected by method of cultivation (CT, conventional tillage; NT, no-tillage) in continuously grown wheat (CW) and after fallow (WF). Values shown are means of four replicates; bars indicate the standard error for comparisons at the same depth where significant differences were found.

by the plant. Although Benbella and Paulsen (1998) demonstrated that KH2PO4 applied at anthesis could act as an effective protectant for drought-stressed wheat, we found no such effect when KH2PO4 was applied to young seedlings. Our lack of results may stem from

inadequate absorption of the applied material. We have recently found (Bonfil and Klein, unpublished, 2001) that PGR application is much more effective at the fourto five-leaf stage when there is adequate leaf area to absorb the material. This may be the result of a broader target area for the spray droplets. El-Antably (1977) found that GA concentrations in wheat seedlings increase two- to threefold from the time plants are at the two- to three-leaf stage to the time they reach four to five leaves. It may be that there was insufficient GA synthesis capacity in younger plants to show a response to inhibitors while in older plants with a greater GA synthesis capacity, the inhibitor effect was more evident. However, PGR effects are not always dramatic, even in more mature plants. Applications of GA3 and paclobutrazol had only very small effects on wheat growth, even when applied at tillering (Guoping, 1997). However, this may have been a function of the concentration and amount of PGR applied. The importance of WF–NT management for dryland farming in marginal desert conditions is supported by our results. No-tillage management increased seedling growth and survival during both 1997–1998 and 1998– 1999 while letting fields lie fallow for a year allowed water to be stored from one season to the next, leading to a further improvement in water availability and final yield in a severe drought season (Bonfil et al., 1999; Smika and Unger, 1986; Thomas et al., 1995). Soil water content of 1% at 120-cm depth is equivalent to 16.8 mm of available water (Bonfil et al., 1999). The annual precipitation in dry years usually ranges from 150 to 180 mm. Therefore, a difference of only 1% in soil water content at sowing can mean a 10% difference in available water during a dry year. In 1999, the soil water present at sowing under WF doubled the total amount of available water during the growing season. Moreover, this water was present in the deeper soil layers during the reproductive stage, thus enhancing its efficiency of use by roots. In contrast, supplying 40 mm of water by late rain or by irrigation did not result in viable plants. In that case, the water fell on dry soil where the roots had already died. Furthermore, even if the plants had been viable, the high temperature occurring at the time of application ensured that evaporation would be rapid. Our results clearly demonstrate that NT with straw mulch management greatly enhances seedling survival in the event of early germination followed by an extended dry period, during drought seasons, or both. This method allows farmers in semiarid or arid regions to sow fields even when the soil is dry, without waiting for an initial rain as suggested by Mahdi et al. (1998). Early sowing in dry soil can decrease the damage that could be caused by cereal cyst nematodes (Heterodera avenae) (Georg et al., 1989) while improving crop growth by increasing the efficient use of the first rains of the season. Moreover, initial crop development can take place before winter weather sets in (in our region, germination would take place in late November), 2 to 3 wk in advance of a field that would be sown later in wet soil. However, sowing time should not be advanced to October because too early a rain ultimately can decrease yield.


In conclusion, NT management is recommended in arid regions, especially for early sowing in dry soil, to ensure seedling survival, plant growth, and grain production. ACKNOWLEDGMENTS This research was financed in part by the Chief Scientist of the Israel Ministry of Agriculture.

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