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Yield performance of spring wheat improved by regulated deficit irrigation in an arid area
Agricultural Water Management 79 (2006) 28–42 www.elsevier.com/locate/agwat
Yield performance of spring wheat improved by regulated deficit irrigation in an arid area Buchong Zhang a,b, Feng-Min Li a,c,*, Gaobao Huang d, Zi-Yong Cheng b, Yanhong Zhang b a
Key Laboratory of Arid Agroecology, School of Life Science, Lanzhou University, Lanzhou, Gansu 730000, China b Department of Water Resources Engineering, Gansu Agricultural University, Lanzhou, Gansu 730070, China c State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences, Yangling, Shaanxi 712100, China d College of Agronomy, Gansu Agricultural University, Lanzhou, Gansu 730070, China Accepted 20 February 2005 Available online 14 March 2005
Abstract A field experiment was conducted in 2003 and 2004 growing seasons to evaluate the effects of regulated deficit irrigation on yield performance in spring wheat (Triticum aestivum) in an arid area. Three regulated deficit irrigation treatments designed to subject the crops to various degrees of soil water deficit at different stages of crop development and a no-soil-water-deficit control was established. Soil moisture was measured gravimetrically in the increment of 0–20 cm every five to seven days in the given growth periods, while that in 20 increments to 40, 40–60, 60–80, and 80– 100 cm depth measured by neutron probe. Compared to the no-soil-water-deficit treatment, grain yield, biomass, harvest index, water use efficiency (WUE), and water supply use efficiency (WsUE) in spring wheat were all greatly improved by 16.6–25.0, 12.4–19.2, 23.5–27.3, 32.7–39.9, and 44.6– 58.8% under regulated deficit irrigation, and better yield components such as thousand-grain weight, grain weight per spike, number of grain, length of spike, and fertile spikelet number were also obtained, but irrigation water was substantially decreased by 14.0–22.9%. The patterns of soil moisture were similar in the regulated deficit treatments, and the soil moisture contents were greatly decreased by regulated deficit irrigation during wheat growing seasons. Significant differences were found between * Corresponding author. Tel.: +86 931 8912848; fax: +86 931 8912848. E-mail address: [email protected] (F.-M. Li). 0378-3774/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2005.02.007
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the no-soil-water-deficit treatment and the regulated soil water deficit treatments in grain yield, yield components, biomass, harvest index, WUE, and WsUE, but no significant differences occurred within the regulated soil water deficit treatments. Yield performance proved that regulated deficit irrigation treatment subjected to medium soil water deficit both during the middle vegetative stage (jointing) and the late reproductive stages (filling and maturity or filling) while subjected to no-soil-water-deficit both during the late vegetative stage (booting) and the early reproductive stage (heading) (MNNM) had the highest yield increase of 25.0 and 14.0% of significant water-saving, therefore, the optimum controlled soil water deficit levels in this study should range 50–60% of field water capacity (FWC) at the middle vegetative growth period (jointing), and 65–70% of FWC at both of the late vegetative period (booting) and early reproductive period (heading) followed by 50–60% of FWC at the late reproductive periods (the end of filling or filling and maturity) in treatment MNNM, with the corresponding optimum total irrigation water of 338 mm. In addition, the relationships among grain yield, biomass, and harvest index, the relationship between grain yield and WUE, WsUE, and the relationship between harvest index and WUE, WsUE under regulated deficit irrigation were also estimated through linear or non-linear regression models, which indicate that the highest grain yield was associated with the maximum biomass, harvest index, and water supply use efficiency, but not with the highest water use efficiency, which was reached by appropriate controlling soil moisture content and water consumption. The relations also indicate that the harvest index was associated with the maximum biomass and water supply use efficiency, but not with the highest water use efficiency. # 2005 Elsevier B.V. All rights reserved. Keywords: Grain yield; Harvest index; Regulated deficit irrigation; Spring wheat (Triticum aestivum); Water use efficiency
1. Introduction As one of the most important ecological factors determining crop growth and development, water deficit plays a very important role in inhibiting the yields of crops. However, water shortage and its serious waste now are the two inconsistency aspects in the usage of water resources worldwide. Due to this reason, in irrigated and dryland agriculture of northwestern China crop production and sustainable development are severely constrained by water limitations during the growing season (Ogola et al., 2002). Thus in order to optimize crop yields and water use efficiency (WUE) in irrigated environments, irrigations should be timed in a way that non-productive soil water evapotranspiration and drainage losses are minimized, and possible inevitable water deficits coincide with least sensitive growth period (Arora and Gajri, 1998). In recent years, many studies about the effects of supplemental irrigation on yield performance and water use efficiency have shown that proper supplemental irrigation can increase crop yield by improving soil water conditions and their WUE significantly (Ehdaie, 1995; Li et al., 1999; HoWell et al., 1998; Deng et al., 2002; Zhang et al., 2004). It has been found that grain yield of spring wheat can be significantly increased about 20– 45% in the same environment by 30–60 mm of reduced irrigation during its jointing (Kang et al., 2002). At present, most researches are focused on how to maintain the best economic productivity and highest WUE under supplemental irrigation in arid and semi-arid areas (Zhang et al., 1998a; Fabeiro et al., 2001, 2002; Stone et al., 2001; Wichelns, 2002; McVicar et al., 2002; Kirnak et al., 2002).
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Different from the irrigation method above, regulated deficit irrigation (RDI) advocates frequent irrigation with small amount of water in proper growth stages under semi-humid but seasonable drought or semiarid environment (Fabeiro et al., 2001; Kang et al., 2002), while supplemental irrigation supports watering more during one or two given growth stages due to the limited stored water by rainfall harvesting in arid or semiarid areas (Zhang et al., 1998b, 2004; Deng et al., 2002). Therefore, RDI has much more advantages in yield increase, water-saving, and WUE improving. With full consideration of the relation between crops and water certain profitable soil water deficits are to be exerted purposefully by RDI in some growth stages of crops to increase future drought resistance ability and optimize distribution of photosynthetic matter in tissues and organs, thus resulting in high grain yield, WUE, and reduction of proportion of nutrient organs in total organic matter (Cai et al., 2002). That is, water deficit is not always the restrictive factor in grain yield and WUE. Contrarily, proper water deficits in certain growth stages are helpful for increase of yield and WUE (Asseng et al., 1998; Plant et al., 1998), mainly because of the supplementary or super supplementary effects for crops caused by limited water deficit, which always results in the consequence that after proper drought and re-watering later several ecological and physiological functions such as photosynthetic rate, stomatal conductance, leaf WUE, percolation regulation ability, etc. will exceed those of full irrigation crops all the time (Zhang et al., 1999). Furthermore, although crop growth is restrained during proper drought stages, energy metabolism and a series of biosynthesis of crops will be intensified, and the water holding capacity will also be improved. This paper reports a study that tried to explore the effectiveness of regulated deficit irrigation on spring wheat production, not only based on the previous studies of RDI under semi-humid but seasonable drought and semiarid environment but also wanted to go a further step in this work in arid areas. So the objectives of this study were to determine: (1) if grain yield, biomass, harvest index, and water use efficiency could be improved through RDI in an arid environment; (2) the relationship among grain yield, biomass, harvest index, and water use efficiency; and (3) the optimum controlled soil water deficit levels and irrigation water at different growth periods.
2. Materials and methods A field experiment was conducted in March–July 2003 and 2004 on a loamy soil in Zhangye, the western area of Gansu Province, PR China (about 998230 E longitude, 418130 N latitude, and 1500 m asl). The climate at the experimental site was characterized by a mean temperature of 5–8 8C, a total solar radiation amount of 558.6–672 kJ cm2, an average rainfall of 139.2 mm and an average evaporation (pan evaporation corrected without pan coefficient) of 2048 mm per year, a cumulative temperature of 1837–2870 8C over 10 8C, and a total none-frost time of about 165 days. The groundwater was 20 m below. The soil was loamy with an average bulk density of 1.39 g cm3 in the upper 60 cm depth. This layer also contains 12.5 g kg1 of total organic matter, 0.88 g kg1 of nitrogen, 0.88 g kg1 phosphate, 13.97 g kg1 potassium, 64.33 mg kg1 of available nitrogen, 11.17 mg kg1 phosphate, and 97 mg kg1 available
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Table 1 Physical and chemical properties of the soil at the experimental site Soil depth (cm)
Organic PH matter (g kg1)
0–20 14.4 20–40 12.0 40–60 11.1
Bulk Total soluble SO42 Total Texture (g kg1) density salinity pore (g cm3) space (%) (g kg1)
8.42 2.47 8.52 2.64 8.56 2.18
0.80 0.40 0.40
1.31 1.43 1.43
50.72 46.76 46.76
Field Wilting capacity point (m3 m3) (m3 m3)
Sandy loam 29.8 Silt loam 32.6 Silt loam 32.6
8.5 9.3 9.3
potassium, respectively, with its pH of 8.5. Some selected physical and chemical properties of the soil are presented in Table 1. The site was divided into plots of 13.9 m 3.5 m size, separated by 1 m buffers which were also sown with wheat irrigated with its irrigation water requirements proportioned to that required in the experimental plots. The plots were arranged in a randomized completeblock design with three replications for each treatment. To prevent horizontal permeation of soil water each plot was isolated in 2 m depth of vertical soil profile through a plastic film. During the preparation of the land, nitrogen (net N of 135 kg ha1) and phosphate (net P2O5 of 75 kg ha1) fertilizers and some manure (0.3 kg dried weight m2) were added as basic fertilizer at sowing. Spring wheat cultivar (Triticum aestivum) ‘Ningchun18’ was sown 6 cm deep on March 14 in both years with the density of 2.1 million seeds/ha in rows of 20 cm, oriented east– west. Seedling density after germination was controlled to around 200 plants/m2. Weeds were removed effectively by hand during all the growing seasons. Pests were also effectively controlled by pesticide in time. All plants were harvested on July 13 in both years. Three regulated deficit irrigation treatments designed to subject the crops to various degrees of soil water deficit at different stages of crop development and a no-soil-waterdeficit control were established (Table 2). Within the two growing seasons, controlled irrigation was applied to each plot with check irrigation using a flow meter connected to the water pipe so as to accurately maintain the soil water deficit level followed by the above experimental design. Although the designed soil water deficit levels were the same in each treatment both during filling and maturity of wheat (Table 2), however, during prephysiological maturity in 2003, the soil moisture in all the treatments (data not shown) varied below the designed lower limits for their more water consumption caused by the relatively higher biomass production than that in 2004 (Table 4). Therefore, to maintain the designed soil moisture ranges, certain amount of irrigation water was applied to each plot. Such situation did not occur in 2004 for their relatively lower biomass production. Thus, there are five periods irrigated in 2003 while four in 2004. Soil moisture was measured gravimetrically in the increment of 0–20 cm using an oven every five to seven days at all the given stages in Table 2, while that in 20 increments to 40, 40–60, 60–80, and 80–100 cm depth measured by neutron probe. At the end of the growing season (13 July in both years), each plot was harvested for biomass (BM) and grain yield. Yield components such as thousand-grain weight (TGW), number of grain (NG), and grain weight per spike (GWPS) were measured on 20 plants per plot. Other economic traits of wheat such as fertile spikelet number (FSN) and length of spike (LS) were also determined.
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Treatment
2003
2004
Jointing
Booting
Heading
Filling
NNNN MNNM MNNS SNNM
65–70 50–60 50–60 45–50
65–70 65–70 65–70 65–70
65–70 65–70 65–70 65–70
65–70 50–60 45–50 50–60
(75) (60) (60) (50)
(105) (90) (75) (75)
(75) (60) (60) (75)
(90) (75) (60) (75)
Maturity
Jointing
Booting
Heading
Jointing
65–70 50–60 45–50 50–60
65–70 50–60 50–60 45–50
65–70 65–70 65–70 65–70
65–70 65–70 65–70 65–70
65–70 50–60 45–50 50–60
(50) (60) (50) (60)
(105) (90) (90) (75)
(105) (90) (75) (75)
(90) (75) (75) (90)
(90) (75) (60) (75)
The growing season was divided into four periods of middle vegetative stage (jointing), late vegetative stage (booting), early reproductive stage (heading), and late reproductive stages (filling and maturity or filling). Soil moisture of no-soil-water-deficit (N), medium soil water deficit (M), and severe water deficit (S) in top 60 cm layer was maintained during different crop growth periods. When soil moisture varied out of the designed range, water was applied immediately to the top of the range.
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Table 2 Controlled soil water content (percentage of field water capacity) of different treatments and irrigation water application (mm) carried out according to the experimental design during the 2003 and 2004 growing seasons
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Soil moisture contents at sowing and harvesting in the whole soil profile were also used to calculate water consumption from soil stored water during the whole growing seasons. Harvest index was calculated as grain yield divided by mature crop biomass. Differences between treatments were examined using ANOVA (‘Statview’, BrainPower Inc., Calabasas, CA). The degree of association between different traits was also estimated through linear or non-linear regression models of the same statistical package.
3. Results 3.1. Soil moisture regimes The patterns of soil moisture were similar in the RDI treatments throughout growing seasons, and the soil moisture dynamics were more acute in the topsoil than that in the subsoil in 2003 (Fig. 1) and 2004 (Fig. 2). After sowing, soil moisture continually decreased in the RDI treatments until 43 days after sowing (DAS), (26 April 2003) and 38 DAS (21 April 2004) in 2003 and 2004 growing seasons respectively, around early jointing, except for that in the top 0–20 and 20–40 cm increments in 2004 due to their lower soil moisture contents at sowing. Soil moisture increased greatly after 43 and 38 DAS due to the regulated irrigation water of 60–105 mm and a small amount of rainfall 2.8–4.9 mm during 45–51 and 47–53 DAS for the two growing seasons (Tables 2 and 3). Such kind of soil moisture increase also appeared at 68–74, 88–94 ,98–104, 108–114 DAS in 2003 and 64– 70, 85–91, 104–110 DAS in 2004 for the same reason. Figs. 1 and 2 also revealed that after 43 and 69 DAS in the two growing seasons soil moisture was always the highest in the no-soil-water-deficit treatments (NNNN) among all the treatments, significantly just at 85, 121, and 80 DAS, respectively. Soil moisture fluctuated more sharply in 2004 growing season than that in 2003 after jointing in all treatments, but that in regulated deficit irrigation plots declined more quickly than that in the no-soil-water-deficit plot. This indicates that after middle vegetative stage some relatively long periods of medium and serious soil water deficit could result in severe soil water consumption, which was responsible for the lower soil moisture contents in these treatments. In addition, four times of irrigation under regulated deficit irrigation not only could increase soil moisture greatly shortly after irrigation than that of five times, but also could result in less water consumption (Figs. 1 and 2). 3.2. Biomass, grain yield, and yield components Table 4 shows that significances occurred in biomass among treatments. The total biomass varied between 1.5 104 and 2.0 104 kg ha1 in the two experimental years. Regulated soil water deficit increased total biomass by 6.7–11.8% in 2003 and 19.3–28.2% in 2004 than that in the no-soil-water-deficit treatment, which was 12.4–19.2% of increase over the 2 years. The minimum total biomass was recorded both in the no-soil-water-deficit NNNN plot with 1.8 104 kg ha1 in 2003 and 1.5 104 kg ha1 in 2004, and the maximum both in regulated soil water deficit treatment MNNM with 2.0 104 and 1.9 104 kg ha1 in the two cropping seasons. Still, no significance occurred between
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Fig. 1. Profile soil moisture content in 0–20, 20–40, 40–80, and 80–100 cm depth for various periods after sowing in northwestern China, 2003. Field crops of spring wheat in NNNN treatment (^) were subjected to no-soil-waterdeficit during the middle vegetative stage (jointing, stage 1), late vegetative stage (booting, stage 2), early reproductive stage (heading, stage 3), and late reproductive stages (filling and maturity or filling, stage 4). Field crops of spring wheat in MNNM treatment (~ ) were subjected to medium soil water deficit during stages 1 and 4 while no-soil-water-deficit during stages 2 and 3. Field crops of spring wheat in MNNS treatment () were subjected to medium soil water deficit during stage 1, severe soil water deficit during stage 4, while no-soil-waterdeficit during stages 2 and 3. Field crops of spring wheat in SNNM treatment (*) were subjected to severe soil water deficit during stage 1, medium water deficit during stage 4, while no-soil-water-deficit during stages 2 and 3. The same in Fig. 2.
treatments MNNS and SNNM. Such performance in biomass production was extremely similar to that in grain yield. As for grain yield and its main components, significance only occurred in grain yield, while fertile spikelet number did not differ among all the treatments, and in thousand-grain weight, number of grain, grain weight per spike, and length of spike, significances only occurred in 2003 growing season (Table 4). Compared to the no-soil-water-deficit treatment NNNN, regulated soil water deficit improved length of spike, fertile spikelet number, grain weight per spike, and number of grain, which indicated these four components may be the combined result of higher thousand-grain weight, and finally higher grain yield. In comparison with the no-soil-water-deficit treatment NNNN, 25.0, 18.9, and 16.6% of yield increase was maintained respectively, in regulated deficit irrigation treatments MNNM, MNNS and SNNM. Therefore, grain yield and most of its components were not reduced by regulated deficit irrigation but greatly improved except for the grain yield in SNNM and thousand-grain weight in MNNM and SNNM in 2004
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Fig. 2. Profile soil moisture content in 0–20, 20–40, 40–80, and 80–100 cm depth for various periods after sowing in northwestern China, 2004.
growing season. That is, the highest grain yield was not produced in the no-soil-waterdeficit treatment but in regulated deficit irrigation treatments. In this study, the highest grain yield was attained in treatment MNNM, which was subjected to medium soil water deficit at the middle vegetative stage (jointing) and late reproductive stages (filling and maturity in 2003 and filling in 2004) while no-soil-water-deficit at the late vegetative stage (booting) and early reproductive stage (heading), but no significant difference occurred between treatments MNNS and SNNM (Table 4). 3.3. Harvest index In 2003 growing season, the harvest indexes ranged from 0.319 to 0.406 with the maximum value of 0.406 in SNNM plot and the minimum 0.319 in NNNN plot (Table 4). The harvest indexes were significantly 23.5–27.3% higher in the three regulated soil water deficit plots than that in the no-soil-water-deficit plot due to their much higher grain yields. Table 3 Monthly rainfall (mm) during the growing seasons in 2003 and 2004 Years
March
April
May
June
July
Total
2003 2004
2.3 2.5
2.8 4.9
14.2 7.8
15.6 18.3
10.5 3.2
45.4 36.7
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Table 4 Grain yield, yield components, biomass, and harvest index subjected to various treatments in 2003 and 2004 growing seasons Years Treatments LS (cm) 2003
2004
FSN
NNNN MNNM MNNS SNNM
7.64 8.49 8.59 8.34
b a a ab
S.E. ()
0.522
NNNN MNNM MNNS SNNM
8.73 9.13 8.96 9.12
S.E. ()
0.406
a a a a
13.3 14.0 14.0 14.1
NG ab a a a
0.443 13.8 14.0 14.1 14.2
a a a a
0.800
34.3 39.7 38.0 38.6
b a ab ab
2.828 40.2 41.2 40.2 40.8
a a a a
2.992
GWPS (g)
TGW (g)
1.73 1.93 1.83 2.01
47.81 52.66 51.99 50.98
b a ab a
0.162 1.98 2.09 2.07 2.01
a a a a
0.049
Total biomass Harvest Grain yield (103 kg ha1) (104 kg ha1) index b a a ab
1.969 48.24 47.74 49.36 47.45
ab ab a ab
0.485
5.6 7.7 7.6 7.6
c a b b
0.4 6.2 7.1 6.4 6.2 0.6
bc a b bc
1.8c 2.0a 1.9ab 1.9b
0.319b 0.394a 0.397a 0.406a
0.04
0.039
1.5c 1.9a 1.8b 1.7b
0.427a 0.379b 0.366b 0.354b
0.07
0.036
Means within columns in the same year followed by the same letter are significantly different at P < 0.05. LS, length of spike; FSN, fertile spikelet number per spike; NG, number of grain per spike; GWPS, grain weight per spike; TGW, thousand-grain weight.
However, no significant differences were found among the regulated soil water deficit plots. Generally speaking, the higher grain yield and relatively lower total biomass in a plot, the higher harvest index attained. Although the grain yield was much higher in MNNM MNNS, and SNNM in 2003, because of their relatively higher total biomass the harvest indexes in these three treatments still remained low. Such phenomenon caused by high total biomass was more obvious in the growing season 2004. As can be seen from Table 4, the harvest indexes were listed 11.2–17.1% lower in the regulated soil water deficit plots in comparison with that in the no-soil-water-deficit plot in 2004, being the reason of their much lower yield than that in 2003. As an exception, an improved harvest index in NNNN plot was found due to its improved grain yield and declined total biomass. However, over the two years the mean harvest indexes in soil water deficit plots were all higher than that in the no-soil-water-deficit plot. Three linear functions were fitted through regression analysis among the data from grain yield, total biomass, and harvest index under regulated deficit irrigation (Figs. 3 and 4). Grain yield increased linearly with the total biomass and harvest index, and the increase in grain yield under different levels of soil water deficit was result of the increase in both total biomass and harvest index, while biomass increased also linearly with the harvest index, which were in line with the data in Figs. 3 and 4. 3.4. Water use efficiency and water supply use efficiency Significances occurred in WUE and water supply use efficiency (WsUE) between the no-soil-water-deficit treatment and regulated deficit irrigation treatments, but no significant differences was found among the regulated deficit irrigation treatments in WUE and WsUE (Table 5). The WUE and WsUE values varied from 14.68 to 16.26 kg ha1 mm1 and from 19.57 to 24.95 kg ha1 mm1 in regulated deficit irrigation
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Fig. 3. Relationship between grain yield (Y) and biomass (BM) for spring wheat under RDI at Zhangye in northwestern PR China.
treatments. Compared to the no-soil-water-deficit treatment, 40.4–42.9 and 25.4–38.9% of WUE and 58.0–76.4 and 29.6–42.2% of WsUE was increased in regulated deficit irrigation treatments in growing season 2003 and 2004, respectively, which was 32.7–39.9 and 44.6– 58.8% of increase over the two years. The maximum WUE and WsUE were recorded in treatment MNNM with 16.26 kg ha1 mm1 and MNNS with 24.95 kg ha1 mm1, respectively, in 2004 and 2003 cropping seasons. The good relationships between WUE and the harvest index, grain yield were quadratic under regulated deficit irrigation (Figs. 5 and 6). In our simulation, the highest WUE of 16.15 and 16.35 kg ha1 mm1 was attained as the harvest index and grain yield approached to the critical values of 0.388 and 7.1 103 kg ha1 around 95.6 and 92.2% of the observed maximum harvest index and grain yield. The results indicated that the maximum WUE was
Fig. 4. Relationships between harvest index (HI) and grain yield (Y), biomass (BM) for spring wheat under RDI at Zhangye in northwestern China.
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Treatment
NNNN MNNM MNNS SNNM
2003
2004
Water supply (mm)
Water use (mm)
WUE (kg ha1 mm1)
WsUE (kg ha1 mm1)
Water supply (mm)
Water use (mm)
WUE (kg ha1 mm1)
WsUE (kg ha1 mm1)
395 345 305 335
496 485 473 481
11.26 15.89 16.09 15.81
14.14 22.34 24.95 22.70
390 330 300 315
503 434 418 420
11.71b 16.26a 15.41ab 14.68ab
15.10b 21.38a 21.47a 19.57ab
b a a a
b ab a ab
WsUE means water supply use efficiency calculated as grain yield divided by seasonal water supply.
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Table 5 Water consumption and water use efficiency subjected to various treatments in 2003 and 2004 growing seasons
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Fig. 5. Relationships between grain yield (Y) and water use efficiency (WUE, *), water supply use efficiency (WsUE, *) for spring wheat under RDI at Zhangye in northwestern China.
not recorded at the maximum harvest index and grain yield, but a little earlier before that. The WUE increased significantly with the harvest index until the critical value mentioned above occurred, followed by a condign decrease of WUE with harvest index, so was with the grain yield in WUE increase. At a low harvest index and grain yield stage, WUE almost linearly increased until a relatively higher WUE was met, after which being a stage of marginal increase of WUE till the critical values of harvest index and grain yield occurred. Figs. 5 and 6 also indicate two linear relations between the WsUE and harvest index, grain yield under regulated deficit irrigation. The results were different from the relations between WUE and the harvest index, grain yield. Therefore to some degree the linearly increased WsUE was the result of increase in harvest index and grain yield.
Fig. 6. Relationships between harvest index (HI) and water use efficiency (WUE, *), water supply use efficiency (WsUE, *) for spring wheat under RDI at Zhangye in northwestern China.
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4. Discussion and conclusions Controlled soil water deficit in the early stage of vegetative growth resulted in a relatively deeper root system (Zhang et al., 1998a) beneficial to a better use of the considerable soil water storage in deeper layers. The intensive decrease of soil moisture in 40–80 and 80–100 cm increments in regulated deficit irrigation treatments MNNM, MNNS, and SNNM (Figs. 1 and 2) indicated that with the wheat growth and root system expansion from the beginning of booting, i.e. 71 and 67 DAS in 2003 and 2004 growing seasons, plants subjected to various soil water deficits increasingly relied on the water in deeper soil layers, while before that only a small amount of water was used in 0–80 cm soil depth, especially less used in 80–100 cm depth, which was consistent with the result reported by Zhang et al. (1998). Grain yield and its main components were higher in the regulated deficit irrigation treatments. Compared to that in the no-soil-water-deficit treatment 16.6–25.0% of yield was improved in regulated deficit irrigation treatments, and 14.0–22.9% of irrigation water was saved (Tables 4 and 5). Therefore, regulated deficit irrigation treatment MNNM had the highest yield increase of 25.0 and 14.0% of significant water-saving effects in arid agricultural production. Obviously, the highest grain yield was not produced in the no-soilwater-deficit treatment. Since the maximum grain yield was maintained in the regulated deficit irrigation treatment MNNM, we assured that the optimum controlled soil water deficit levels in this study would be: 50–60% of field water capacity (FWC) at the middle vegetative growth period (jointing), and 65–70% of FWC at both of the late vegetative period (booting) and early reproductive period (heading) followed by 50–60% of FWC at the late reproductive periods (the end of filling or filling and maturity). Correspondingly, the optimum total irrigation water would be 338 mm in treatment MNNM. But it should be noted that treatment MNNS could be regarded as an alternative treatment to choose because of its slightly 4.9% of yield decrease and 8.9% of reduction in irrigation water, which had the same soil water deficit level as MNNM except for a 45–50% of FWC of soil moisture level at the late reproductive periods with the total irrigation water of 303 mm. Thus, water resources can be scientifically saved through such processes above. Such results coincided with that from Kang et al. (2002) and the conclusions can be helpful for the sustainable agriculture development in arid areas. There were significant differences between the no-soil-water-deficit treatment and the regulated deficit irrigation treatments in grain yield, yield components, total biomass, WUE, WsUE and harvest index over both growing seasons, but within the regulated deficit irrigation treatments significances only occurred in grain yield and total biomass. The relationships between grain yield and the biomass, harvest index, WsUE under regulated deficit irrigation were linear, so were between the harvest index and biomass, WsUE. However, the relations between WUE and harvest index, grain yield could be described by quadratic equations. These relationships indicate that the highest grain yield was associated with the maximum biomass, harvest index, and water supply use efficiency, but not with the highest water use efficiency, which was reached by appropriate controlling soil moisture content and water consumption. The relations also indicate that the harvest index was associated with the maximum biomass and water supply use efficiency, but not with the highest water use efficiency. However, because of the different experimental
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conditions from the previous studies such conclusions above were partly supported by Zhang et al. (1998) and Kang et al. (2002). In most cases of semi-humid but seasonable drought or semiarid areas of the world, regulated deficit irrigation has significant effect on yield increase and water-saving. This research explores the effectiveness of regulated deficit irrigation on spring wheat in an arid environment. Appropriate degree of regulated deficit irrigation at the middle vegetative growth period (jointing), the late vegetative period (booting), the early reproductive period (heading), and the late reproductive periods (the end of filling or filling and maturity) could result in high grain yield, total biomass, water use efficiency, water supply use efficiency, harvest index, and better yield components in spring wheat in an arid environment. The optimum soil water deficit levels with highest grain yield, total biomass, water use efficiency, water supply use efficiency, harvest index and better yield components were proved to be 50–60, 65–70, 65–70, and 50–60% of field water capacity at the four growth stages above mentioned, with the corresponding optimum total irrigation water of 338 mm (averaged by present only two years of limited data in order to give a full consideration of the climatic variability) which was distributed as following: 75 mm during the middle vegetative stage (jointing), 90 mm during the late vegetative stage (booting), 68 mm during the early reproductive stage (heading), and 105 mm during the late reproductive stage (filling to maturity). Nevertheless, soil moisture contents were greatly decreased by regulated deficit irrigation during wheat growing seasons.
Acknowledgements This research was supported by NKBRSF Project of China (G2000018603) and Hundred-Talent Program project of CAS.
References Arora, V.K., Gajri, P.R., 1998. Evaluation of a crop growth-water balance model for analyzing wheat responses to climate- and water-limited environment. Field Crops Res. 59, 213–224. Asseng, S., Ritchie, J.T., Smucker, A.J.M., Robertson, M.J., 1998. Root growth and water uptake during water deficit and recovering in wheat. Plant soil 201, 265–273. Cai, H., Kang, S., Zhang, Z., Chai, H., Hu, X., Wang, J., 2002. Proper growth stages and deficit degree of crop regulated deficit irrigation. Trans. CSAE 16 (3), 24–27 (in Chinese). Deng, X., Shan, L., Shinobu, I., 2002. High efficient use of limited supplement water by dryland spring wheat. Trans. CSAE 18 (5), 84–91. Ehdaie, B., 1995. Variation in water use efficiency and its components in wheat. II. Pot and field experiments. Crop Sci. 35 (6), 1617–1625. Fabeiro, C., Martin de Santa Olalla, F., de Juan, J.A., 2001. Yield and size of deficit irrigated potatoes. Agric. Water Manage. 48, 255–266. Fabeiro, C., Martin de Santa Olalla, F., de Juan, J.A., 2002. Production of muskmelon (Cucumis melo L.) under controlled deficit irrigation in a semi-arid climate. Agric. Water Manage. 54, 93–105. HoWell, T.A., Tolk, J.A., Schneider, A.D., Evett, S.R., 1998. Evapotranspiration, yield, and water use efficiency of corn hybrids differing in maturity. Agron. J. 90 (1), 3–9. Kang, S., Zhang, L., Ling, Y., Hu, X., Cai, H., Gu, B., 2002. Effects of limited irrigation on yield and water use efficiency of winter wheat in the loess plateau of China. Agric. Water Manage. 55, 203–216.
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Kirnak, H., Tas, I., Kaya, C., Higgs, D., 2002. Effects of deficit irrigation on growth, yield, and fruit quality of eggplant under semi-arid conditions. Aust. J. Agric. Res. 53, 1367–1373. Li, F.M., Guo, A.H., Wei, H., 1999. Effects of clear plastic film mulch on yield of spring wheat. Field Crops Res. 63, 79–86. McVicar, T.R., Zhang, G., Bradford, A.S., Wang, H., Dawes, W.R., Zhang, L., Li, L., 2002. Monitoring regional agricultural water use efficiency for Hebei Province on the North China Plain. Aust. J. Agric. Res. 53, 55–76. Ogola, J.B.O., Wheeler, T.R., Harris, P.M., 2002. Effects of nitrogen and irrigation on water use of maize crops. Field Crops Res. 78, 105–117. Plant, J., Rerkasem, B., Noppakoonwong, R., 1998. Effect of water stress on the boron response of wheat genotypes under low boron field conditions. Plant Soil 202, 193–200. Stone, P.J., Wilson, D.R., Beid, J.B., Gillespie, R.N., 2001. Water deficit effects on sweet corn I. water use, radiation use efficiency, growth, and yield. Aust. J. Agric. Res. 52, 103–113. Wichelns, D., 2002. An economic prospective on the potential grains from improvements in irrigation water management. Agric. Water Manage. 52, 233–248. Zhang, B., Li, F., Cheng, Z., 2004. Temporal and spatial dynamics of soil moisture in intercropped maize under deficit irrigation with rainfall harvesting. J. Irrigation Drainage 23 (2), 49–51 (in Chinese). Zhang, H., Oweis, T.Y., Garabet, S., Pala, M., 1998a. Water use efficiency and transpiration efficiency of wheat under rain-fed conditions and supplemental irrigation in a Mediterranean-type environment. Plant Soil 201, 295–305. Zhang, J., Sui, X., Li, B., Su, B., Li, J., Zhou, D., 1998b. An improved water-use efficiency for winter wheat grown under reduced irrigation. Field Crops Res. 59, 91–98. Zhang, X., You, M., Wang, X., 1999. Effects of water deficits on winter wheat yield during its different development stage. Acta Agric. Boreali-Sinica 14 (2), 79–83 (in Chinese).
Yield performance of spring wheat improved by regulated deficit irrigation in an arid area Buchong Zhang a,b, Feng-Min Li a,c,*, Gaobao Huang d, Zi-Yong Cheng b, Yanhong Zhang b a
Key Laboratory of Arid Agroecology, School of Life Science, Lanzhou University, Lanzhou, Gansu 730000, China b Department of Water Resources Engineering, Gansu Agricultural University, Lanzhou, Gansu 730070, China c State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences, Yangling, Shaanxi 712100, China d College of Agronomy, Gansu Agricultural University, Lanzhou, Gansu 730070, China Accepted 20 February 2005 Available online 14 March 2005
Abstract A field experiment was conducted in 2003 and 2004 growing seasons to evaluate the effects of regulated deficit irrigation on yield performance in spring wheat (Triticum aestivum) in an arid area. Three regulated deficit irrigation treatments designed to subject the crops to various degrees of soil water deficit at different stages of crop development and a no-soil-water-deficit control was established. Soil moisture was measured gravimetrically in the increment of 0–20 cm every five to seven days in the given growth periods, while that in 20 increments to 40, 40–60, 60–80, and 80– 100 cm depth measured by neutron probe. Compared to the no-soil-water-deficit treatment, grain yield, biomass, harvest index, water use efficiency (WUE), and water supply use efficiency (WsUE) in spring wheat were all greatly improved by 16.6–25.0, 12.4–19.2, 23.5–27.3, 32.7–39.9, and 44.6– 58.8% under regulated deficit irrigation, and better yield components such as thousand-grain weight, grain weight per spike, number of grain, length of spike, and fertile spikelet number were also obtained, but irrigation water was substantially decreased by 14.0–22.9%. The patterns of soil moisture were similar in the regulated deficit treatments, and the soil moisture contents were greatly decreased by regulated deficit irrigation during wheat growing seasons. Significant differences were found between * Corresponding author. Tel.: +86 931 8912848; fax: +86 931 8912848. E-mail address: [email protected] (F.-M. Li). 0378-3774/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2005.02.007
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the no-soil-water-deficit treatment and the regulated soil water deficit treatments in grain yield, yield components, biomass, harvest index, WUE, and WsUE, but no significant differences occurred within the regulated soil water deficit treatments. Yield performance proved that regulated deficit irrigation treatment subjected to medium soil water deficit both during the middle vegetative stage (jointing) and the late reproductive stages (filling and maturity or filling) while subjected to no-soil-water-deficit both during the late vegetative stage (booting) and the early reproductive stage (heading) (MNNM) had the highest yield increase of 25.0 and 14.0% of significant water-saving, therefore, the optimum controlled soil water deficit levels in this study should range 50–60% of field water capacity (FWC) at the middle vegetative growth period (jointing), and 65–70% of FWC at both of the late vegetative period (booting) and early reproductive period (heading) followed by 50–60% of FWC at the late reproductive periods (the end of filling or filling and maturity) in treatment MNNM, with the corresponding optimum total irrigation water of 338 mm. In addition, the relationships among grain yield, biomass, and harvest index, the relationship between grain yield and WUE, WsUE, and the relationship between harvest index and WUE, WsUE under regulated deficit irrigation were also estimated through linear or non-linear regression models, which indicate that the highest grain yield was associated with the maximum biomass, harvest index, and water supply use efficiency, but not with the highest water use efficiency, which was reached by appropriate controlling soil moisture content and water consumption. The relations also indicate that the harvest index was associated with the maximum biomass and water supply use efficiency, but not with the highest water use efficiency. # 2005 Elsevier B.V. All rights reserved. Keywords: Grain yield; Harvest index; Regulated deficit irrigation; Spring wheat (Triticum aestivum); Water use efficiency
1. Introduction As one of the most important ecological factors determining crop growth and development, water deficit plays a very important role in inhibiting the yields of crops. However, water shortage and its serious waste now are the two inconsistency aspects in the usage of water resources worldwide. Due to this reason, in irrigated and dryland agriculture of northwestern China crop production and sustainable development are severely constrained by water limitations during the growing season (Ogola et al., 2002). Thus in order to optimize crop yields and water use efficiency (WUE) in irrigated environments, irrigations should be timed in a way that non-productive soil water evapotranspiration and drainage losses are minimized, and possible inevitable water deficits coincide with least sensitive growth period (Arora and Gajri, 1998). In recent years, many studies about the effects of supplemental irrigation on yield performance and water use efficiency have shown that proper supplemental irrigation can increase crop yield by improving soil water conditions and their WUE significantly (Ehdaie, 1995; Li et al., 1999; HoWell et al., 1998; Deng et al., 2002; Zhang et al., 2004). It has been found that grain yield of spring wheat can be significantly increased about 20– 45% in the same environment by 30–60 mm of reduced irrigation during its jointing (Kang et al., 2002). At present, most researches are focused on how to maintain the best economic productivity and highest WUE under supplemental irrigation in arid and semi-arid areas (Zhang et al., 1998a; Fabeiro et al., 2001, 2002; Stone et al., 2001; Wichelns, 2002; McVicar et al., 2002; Kirnak et al., 2002).
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Different from the irrigation method above, regulated deficit irrigation (RDI) advocates frequent irrigation with small amount of water in proper growth stages under semi-humid but seasonable drought or semiarid environment (Fabeiro et al., 2001; Kang et al., 2002), while supplemental irrigation supports watering more during one or two given growth stages due to the limited stored water by rainfall harvesting in arid or semiarid areas (Zhang et al., 1998b, 2004; Deng et al., 2002). Therefore, RDI has much more advantages in yield increase, water-saving, and WUE improving. With full consideration of the relation between crops and water certain profitable soil water deficits are to be exerted purposefully by RDI in some growth stages of crops to increase future drought resistance ability and optimize distribution of photosynthetic matter in tissues and organs, thus resulting in high grain yield, WUE, and reduction of proportion of nutrient organs in total organic matter (Cai et al., 2002). That is, water deficit is not always the restrictive factor in grain yield and WUE. Contrarily, proper water deficits in certain growth stages are helpful for increase of yield and WUE (Asseng et al., 1998; Plant et al., 1998), mainly because of the supplementary or super supplementary effects for crops caused by limited water deficit, which always results in the consequence that after proper drought and re-watering later several ecological and physiological functions such as photosynthetic rate, stomatal conductance, leaf WUE, percolation regulation ability, etc. will exceed those of full irrigation crops all the time (Zhang et al., 1999). Furthermore, although crop growth is restrained during proper drought stages, energy metabolism and a series of biosynthesis of crops will be intensified, and the water holding capacity will also be improved. This paper reports a study that tried to explore the effectiveness of regulated deficit irrigation on spring wheat production, not only based on the previous studies of RDI under semi-humid but seasonable drought and semiarid environment but also wanted to go a further step in this work in arid areas. So the objectives of this study were to determine: (1) if grain yield, biomass, harvest index, and water use efficiency could be improved through RDI in an arid environment; (2) the relationship among grain yield, biomass, harvest index, and water use efficiency; and (3) the optimum controlled soil water deficit levels and irrigation water at different growth periods.
2. Materials and methods A field experiment was conducted in March–July 2003 and 2004 on a loamy soil in Zhangye, the western area of Gansu Province, PR China (about 998230 E longitude, 418130 N latitude, and 1500 m asl). The climate at the experimental site was characterized by a mean temperature of 5–8 8C, a total solar radiation amount of 558.6–672 kJ cm2, an average rainfall of 139.2 mm and an average evaporation (pan evaporation corrected without pan coefficient) of 2048 mm per year, a cumulative temperature of 1837–2870 8C over 10 8C, and a total none-frost time of about 165 days. The groundwater was 20 m below. The soil was loamy with an average bulk density of 1.39 g cm3 in the upper 60 cm depth. This layer also contains 12.5 g kg1 of total organic matter, 0.88 g kg1 of nitrogen, 0.88 g kg1 phosphate, 13.97 g kg1 potassium, 64.33 mg kg1 of available nitrogen, 11.17 mg kg1 phosphate, and 97 mg kg1 available
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Table 1 Physical and chemical properties of the soil at the experimental site Soil depth (cm)
Organic PH matter (g kg1)
0–20 14.4 20–40 12.0 40–60 11.1
Bulk Total soluble SO42 Total Texture (g kg1) density salinity pore (g cm3) space (%) (g kg1)
8.42 2.47 8.52 2.64 8.56 2.18
0.80 0.40 0.40
1.31 1.43 1.43
50.72 46.76 46.76
Field Wilting capacity point (m3 m3) (m3 m3)
Sandy loam 29.8 Silt loam 32.6 Silt loam 32.6
8.5 9.3 9.3
potassium, respectively, with its pH of 8.5. Some selected physical and chemical properties of the soil are presented in Table 1. The site was divided into plots of 13.9 m 3.5 m size, separated by 1 m buffers which were also sown with wheat irrigated with its irrigation water requirements proportioned to that required in the experimental plots. The plots were arranged in a randomized completeblock design with three replications for each treatment. To prevent horizontal permeation of soil water each plot was isolated in 2 m depth of vertical soil profile through a plastic film. During the preparation of the land, nitrogen (net N of 135 kg ha1) and phosphate (net P2O5 of 75 kg ha1) fertilizers and some manure (0.3 kg dried weight m2) were added as basic fertilizer at sowing. Spring wheat cultivar (Triticum aestivum) ‘Ningchun18’ was sown 6 cm deep on March 14 in both years with the density of 2.1 million seeds/ha in rows of 20 cm, oriented east– west. Seedling density after germination was controlled to around 200 plants/m2. Weeds were removed effectively by hand during all the growing seasons. Pests were also effectively controlled by pesticide in time. All plants were harvested on July 13 in both years. Three regulated deficit irrigation treatments designed to subject the crops to various degrees of soil water deficit at different stages of crop development and a no-soil-waterdeficit control were established (Table 2). Within the two growing seasons, controlled irrigation was applied to each plot with check irrigation using a flow meter connected to the water pipe so as to accurately maintain the soil water deficit level followed by the above experimental design. Although the designed soil water deficit levels were the same in each treatment both during filling and maturity of wheat (Table 2), however, during prephysiological maturity in 2003, the soil moisture in all the treatments (data not shown) varied below the designed lower limits for their more water consumption caused by the relatively higher biomass production than that in 2004 (Table 4). Therefore, to maintain the designed soil moisture ranges, certain amount of irrigation water was applied to each plot. Such situation did not occur in 2004 for their relatively lower biomass production. Thus, there are five periods irrigated in 2003 while four in 2004. Soil moisture was measured gravimetrically in the increment of 0–20 cm using an oven every five to seven days at all the given stages in Table 2, while that in 20 increments to 40, 40–60, 60–80, and 80–100 cm depth measured by neutron probe. At the end of the growing season (13 July in both years), each plot was harvested for biomass (BM) and grain yield. Yield components such as thousand-grain weight (TGW), number of grain (NG), and grain weight per spike (GWPS) were measured on 20 plants per plot. Other economic traits of wheat such as fertile spikelet number (FSN) and length of spike (LS) were also determined.
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Treatment
2003
2004
Jointing
Booting
Heading
Filling
NNNN MNNM MNNS SNNM
65–70 50–60 50–60 45–50
65–70 65–70 65–70 65–70
65–70 65–70 65–70 65–70
65–70 50–60 45–50 50–60
(75) (60) (60) (50)
(105) (90) (75) (75)
(75) (60) (60) (75)
(90) (75) (60) (75)
Maturity
Jointing
Booting
Heading
Jointing
65–70 50–60 45–50 50–60
65–70 50–60 50–60 45–50
65–70 65–70 65–70 65–70
65–70 65–70 65–70 65–70
65–70 50–60 45–50 50–60
(50) (60) (50) (60)
(105) (90) (90) (75)
(105) (90) (75) (75)
(90) (75) (75) (90)
(90) (75) (60) (75)
The growing season was divided into four periods of middle vegetative stage (jointing), late vegetative stage (booting), early reproductive stage (heading), and late reproductive stages (filling and maturity or filling). Soil moisture of no-soil-water-deficit (N), medium soil water deficit (M), and severe water deficit (S) in top 60 cm layer was maintained during different crop growth periods. When soil moisture varied out of the designed range, water was applied immediately to the top of the range.
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Table 2 Controlled soil water content (percentage of field water capacity) of different treatments and irrigation water application (mm) carried out according to the experimental design during the 2003 and 2004 growing seasons
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Soil moisture contents at sowing and harvesting in the whole soil profile were also used to calculate water consumption from soil stored water during the whole growing seasons. Harvest index was calculated as grain yield divided by mature crop biomass. Differences between treatments were examined using ANOVA (‘Statview’, BrainPower Inc., Calabasas, CA). The degree of association between different traits was also estimated through linear or non-linear regression models of the same statistical package.
3. Results 3.1. Soil moisture regimes The patterns of soil moisture were similar in the RDI treatments throughout growing seasons, and the soil moisture dynamics were more acute in the topsoil than that in the subsoil in 2003 (Fig. 1) and 2004 (Fig. 2). After sowing, soil moisture continually decreased in the RDI treatments until 43 days after sowing (DAS), (26 April 2003) and 38 DAS (21 April 2004) in 2003 and 2004 growing seasons respectively, around early jointing, except for that in the top 0–20 and 20–40 cm increments in 2004 due to their lower soil moisture contents at sowing. Soil moisture increased greatly after 43 and 38 DAS due to the regulated irrigation water of 60–105 mm and a small amount of rainfall 2.8–4.9 mm during 45–51 and 47–53 DAS for the two growing seasons (Tables 2 and 3). Such kind of soil moisture increase also appeared at 68–74, 88–94 ,98–104, 108–114 DAS in 2003 and 64– 70, 85–91, 104–110 DAS in 2004 for the same reason. Figs. 1 and 2 also revealed that after 43 and 69 DAS in the two growing seasons soil moisture was always the highest in the no-soil-water-deficit treatments (NNNN) among all the treatments, significantly just at 85, 121, and 80 DAS, respectively. Soil moisture fluctuated more sharply in 2004 growing season than that in 2003 after jointing in all treatments, but that in regulated deficit irrigation plots declined more quickly than that in the no-soil-water-deficit plot. This indicates that after middle vegetative stage some relatively long periods of medium and serious soil water deficit could result in severe soil water consumption, which was responsible for the lower soil moisture contents in these treatments. In addition, four times of irrigation under regulated deficit irrigation not only could increase soil moisture greatly shortly after irrigation than that of five times, but also could result in less water consumption (Figs. 1 and 2). 3.2. Biomass, grain yield, and yield components Table 4 shows that significances occurred in biomass among treatments. The total biomass varied between 1.5 104 and 2.0 104 kg ha1 in the two experimental years. Regulated soil water deficit increased total biomass by 6.7–11.8% in 2003 and 19.3–28.2% in 2004 than that in the no-soil-water-deficit treatment, which was 12.4–19.2% of increase over the 2 years. The minimum total biomass was recorded both in the no-soil-water-deficit NNNN plot with 1.8 104 kg ha1 in 2003 and 1.5 104 kg ha1 in 2004, and the maximum both in regulated soil water deficit treatment MNNM with 2.0 104 and 1.9 104 kg ha1 in the two cropping seasons. Still, no significance occurred between
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Fig. 1. Profile soil moisture content in 0–20, 20–40, 40–80, and 80–100 cm depth for various periods after sowing in northwestern China, 2003. Field crops of spring wheat in NNNN treatment (^) were subjected to no-soil-waterdeficit during the middle vegetative stage (jointing, stage 1), late vegetative stage (booting, stage 2), early reproductive stage (heading, stage 3), and late reproductive stages (filling and maturity or filling, stage 4). Field crops of spring wheat in MNNM treatment (~ ) were subjected to medium soil water deficit during stages 1 and 4 while no-soil-water-deficit during stages 2 and 3. Field crops of spring wheat in MNNS treatment () were subjected to medium soil water deficit during stage 1, severe soil water deficit during stage 4, while no-soil-waterdeficit during stages 2 and 3. Field crops of spring wheat in SNNM treatment (*) were subjected to severe soil water deficit during stage 1, medium water deficit during stage 4, while no-soil-water-deficit during stages 2 and 3. The same in Fig. 2.
treatments MNNS and SNNM. Such performance in biomass production was extremely similar to that in grain yield. As for grain yield and its main components, significance only occurred in grain yield, while fertile spikelet number did not differ among all the treatments, and in thousand-grain weight, number of grain, grain weight per spike, and length of spike, significances only occurred in 2003 growing season (Table 4). Compared to the no-soil-water-deficit treatment NNNN, regulated soil water deficit improved length of spike, fertile spikelet number, grain weight per spike, and number of grain, which indicated these four components may be the combined result of higher thousand-grain weight, and finally higher grain yield. In comparison with the no-soil-water-deficit treatment NNNN, 25.0, 18.9, and 16.6% of yield increase was maintained respectively, in regulated deficit irrigation treatments MNNM, MNNS and SNNM. Therefore, grain yield and most of its components were not reduced by regulated deficit irrigation but greatly improved except for the grain yield in SNNM and thousand-grain weight in MNNM and SNNM in 2004
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Fig. 2. Profile soil moisture content in 0–20, 20–40, 40–80, and 80–100 cm depth for various periods after sowing in northwestern China, 2004.
growing season. That is, the highest grain yield was not produced in the no-soil-waterdeficit treatment but in regulated deficit irrigation treatments. In this study, the highest grain yield was attained in treatment MNNM, which was subjected to medium soil water deficit at the middle vegetative stage (jointing) and late reproductive stages (filling and maturity in 2003 and filling in 2004) while no-soil-water-deficit at the late vegetative stage (booting) and early reproductive stage (heading), but no significant difference occurred between treatments MNNS and SNNM (Table 4). 3.3. Harvest index In 2003 growing season, the harvest indexes ranged from 0.319 to 0.406 with the maximum value of 0.406 in SNNM plot and the minimum 0.319 in NNNN plot (Table 4). The harvest indexes were significantly 23.5–27.3% higher in the three regulated soil water deficit plots than that in the no-soil-water-deficit plot due to their much higher grain yields. Table 3 Monthly rainfall (mm) during the growing seasons in 2003 and 2004 Years
March
April
May
June
July
Total
2003 2004
2.3 2.5
2.8 4.9
14.2 7.8
15.6 18.3
10.5 3.2
45.4 36.7
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Table 4 Grain yield, yield components, biomass, and harvest index subjected to various treatments in 2003 and 2004 growing seasons Years Treatments LS (cm) 2003
2004
FSN
NNNN MNNM MNNS SNNM
7.64 8.49 8.59 8.34
b a a ab
S.E. ()
0.522
NNNN MNNM MNNS SNNM
8.73 9.13 8.96 9.12
S.E. ()
0.406
a a a a
13.3 14.0 14.0 14.1
NG ab a a a
0.443 13.8 14.0 14.1 14.2
a a a a
0.800
34.3 39.7 38.0 38.6
b a ab ab
2.828 40.2 41.2 40.2 40.8
a a a a
2.992
GWPS (g)
TGW (g)
1.73 1.93 1.83 2.01
47.81 52.66 51.99 50.98
b a ab a
0.162 1.98 2.09 2.07 2.01
a a a a
0.049
Total biomass Harvest Grain yield (103 kg ha1) (104 kg ha1) index b a a ab
1.969 48.24 47.74 49.36 47.45
ab ab a ab
0.485
5.6 7.7 7.6 7.6
c a b b
0.4 6.2 7.1 6.4 6.2 0.6
bc a b bc
1.8c 2.0a 1.9ab 1.9b
0.319b 0.394a 0.397a 0.406a
0.04
0.039
1.5c 1.9a 1.8b 1.7b
0.427a 0.379b 0.366b 0.354b
0.07
0.036
Means within columns in the same year followed by the same letter are significantly different at P < 0.05. LS, length of spike; FSN, fertile spikelet number per spike; NG, number of grain per spike; GWPS, grain weight per spike; TGW, thousand-grain weight.
However, no significant differences were found among the regulated soil water deficit plots. Generally speaking, the higher grain yield and relatively lower total biomass in a plot, the higher harvest index attained. Although the grain yield was much higher in MNNM MNNS, and SNNM in 2003, because of their relatively higher total biomass the harvest indexes in these three treatments still remained low. Such phenomenon caused by high total biomass was more obvious in the growing season 2004. As can be seen from Table 4, the harvest indexes were listed 11.2–17.1% lower in the regulated soil water deficit plots in comparison with that in the no-soil-water-deficit plot in 2004, being the reason of their much lower yield than that in 2003. As an exception, an improved harvest index in NNNN plot was found due to its improved grain yield and declined total biomass. However, over the two years the mean harvest indexes in soil water deficit plots were all higher than that in the no-soil-water-deficit plot. Three linear functions were fitted through regression analysis among the data from grain yield, total biomass, and harvest index under regulated deficit irrigation (Figs. 3 and 4). Grain yield increased linearly with the total biomass and harvest index, and the increase in grain yield under different levels of soil water deficit was result of the increase in both total biomass and harvest index, while biomass increased also linearly with the harvest index, which were in line with the data in Figs. 3 and 4. 3.4. Water use efficiency and water supply use efficiency Significances occurred in WUE and water supply use efficiency (WsUE) between the no-soil-water-deficit treatment and regulated deficit irrigation treatments, but no significant differences was found among the regulated deficit irrigation treatments in WUE and WsUE (Table 5). The WUE and WsUE values varied from 14.68 to 16.26 kg ha1 mm1 and from 19.57 to 24.95 kg ha1 mm1 in regulated deficit irrigation
B. Zhang et al. / Agricultural Water Management 79 (2006) 28–42
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Fig. 3. Relationship between grain yield (Y) and biomass (BM) for spring wheat under RDI at Zhangye in northwestern PR China.
treatments. Compared to the no-soil-water-deficit treatment, 40.4–42.9 and 25.4–38.9% of WUE and 58.0–76.4 and 29.6–42.2% of WsUE was increased in regulated deficit irrigation treatments in growing season 2003 and 2004, respectively, which was 32.7–39.9 and 44.6– 58.8% of increase over the two years. The maximum WUE and WsUE were recorded in treatment MNNM with 16.26 kg ha1 mm1 and MNNS with 24.95 kg ha1 mm1, respectively, in 2004 and 2003 cropping seasons. The good relationships between WUE and the harvest index, grain yield were quadratic under regulated deficit irrigation (Figs. 5 and 6). In our simulation, the highest WUE of 16.15 and 16.35 kg ha1 mm1 was attained as the harvest index and grain yield approached to the critical values of 0.388 and 7.1 103 kg ha1 around 95.6 and 92.2% of the observed maximum harvest index and grain yield. The results indicated that the maximum WUE was
Fig. 4. Relationships between harvest index (HI) and grain yield (Y), biomass (BM) for spring wheat under RDI at Zhangye in northwestern China.
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Treatment
NNNN MNNM MNNS SNNM
2003
2004
Water supply (mm)
Water use (mm)
WUE (kg ha1 mm1)
WsUE (kg ha1 mm1)
Water supply (mm)
Water use (mm)
WUE (kg ha1 mm1)
WsUE (kg ha1 mm1)
395 345 305 335
496 485 473 481
11.26 15.89 16.09 15.81
14.14 22.34 24.95 22.70
390 330 300 315
503 434 418 420
11.71b 16.26a 15.41ab 14.68ab
15.10b 21.38a 21.47a 19.57ab
b a a a
b ab a ab
WsUE means water supply use efficiency calculated as grain yield divided by seasonal water supply.
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Table 5 Water consumption and water use efficiency subjected to various treatments in 2003 and 2004 growing seasons
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Fig. 5. Relationships between grain yield (Y) and water use efficiency (WUE, *), water supply use efficiency (WsUE, *) for spring wheat under RDI at Zhangye in northwestern China.
not recorded at the maximum harvest index and grain yield, but a little earlier before that. The WUE increased significantly with the harvest index until the critical value mentioned above occurred, followed by a condign decrease of WUE with harvest index, so was with the grain yield in WUE increase. At a low harvest index and grain yield stage, WUE almost linearly increased until a relatively higher WUE was met, after which being a stage of marginal increase of WUE till the critical values of harvest index and grain yield occurred. Figs. 5 and 6 also indicate two linear relations between the WsUE and harvest index, grain yield under regulated deficit irrigation. The results were different from the relations between WUE and the harvest index, grain yield. Therefore to some degree the linearly increased WsUE was the result of increase in harvest index and grain yield.
Fig. 6. Relationships between harvest index (HI) and water use efficiency (WUE, *), water supply use efficiency (WsUE, *) for spring wheat under RDI at Zhangye in northwestern China.
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4. Discussion and conclusions Controlled soil water deficit in the early stage of vegetative growth resulted in a relatively deeper root system (Zhang et al., 1998a) beneficial to a better use of the considerable soil water storage in deeper layers. The intensive decrease of soil moisture in 40–80 and 80–100 cm increments in regulated deficit irrigation treatments MNNM, MNNS, and SNNM (Figs. 1 and 2) indicated that with the wheat growth and root system expansion from the beginning of booting, i.e. 71 and 67 DAS in 2003 and 2004 growing seasons, plants subjected to various soil water deficits increasingly relied on the water in deeper soil layers, while before that only a small amount of water was used in 0–80 cm soil depth, especially less used in 80–100 cm depth, which was consistent with the result reported by Zhang et al. (1998). Grain yield and its main components were higher in the regulated deficit irrigation treatments. Compared to that in the no-soil-water-deficit treatment 16.6–25.0% of yield was improved in regulated deficit irrigation treatments, and 14.0–22.9% of irrigation water was saved (Tables 4 and 5). Therefore, regulated deficit irrigation treatment MNNM had the highest yield increase of 25.0 and 14.0% of significant water-saving effects in arid agricultural production. Obviously, the highest grain yield was not produced in the no-soilwater-deficit treatment. Since the maximum grain yield was maintained in the regulated deficit irrigation treatment MNNM, we assured that the optimum controlled soil water deficit levels in this study would be: 50–60% of field water capacity (FWC) at the middle vegetative growth period (jointing), and 65–70% of FWC at both of the late vegetative period (booting) and early reproductive period (heading) followed by 50–60% of FWC at the late reproductive periods (the end of filling or filling and maturity). Correspondingly, the optimum total irrigation water would be 338 mm in treatment MNNM. But it should be noted that treatment MNNS could be regarded as an alternative treatment to choose because of its slightly 4.9% of yield decrease and 8.9% of reduction in irrigation water, which had the same soil water deficit level as MNNM except for a 45–50% of FWC of soil moisture level at the late reproductive periods with the total irrigation water of 303 mm. Thus, water resources can be scientifically saved through such processes above. Such results coincided with that from Kang et al. (2002) and the conclusions can be helpful for the sustainable agriculture development in arid areas. There were significant differences between the no-soil-water-deficit treatment and the regulated deficit irrigation treatments in grain yield, yield components, total biomass, WUE, WsUE and harvest index over both growing seasons, but within the regulated deficit irrigation treatments significances only occurred in grain yield and total biomass. The relationships between grain yield and the biomass, harvest index, WsUE under regulated deficit irrigation were linear, so were between the harvest index and biomass, WsUE. However, the relations between WUE and harvest index, grain yield could be described by quadratic equations. These relationships indicate that the highest grain yield was associated with the maximum biomass, harvest index, and water supply use efficiency, but not with the highest water use efficiency, which was reached by appropriate controlling soil moisture content and water consumption. The relations also indicate that the harvest index was associated with the maximum biomass and water supply use efficiency, but not with the highest water use efficiency. However, because of the different experimental
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conditions from the previous studies such conclusions above were partly supported by Zhang et al. (1998) and Kang et al. (2002). In most cases of semi-humid but seasonable drought or semiarid areas of the world, regulated deficit irrigation has significant effect on yield increase and water-saving. This research explores the effectiveness of regulated deficit irrigation on spring wheat in an arid environment. Appropriate degree of regulated deficit irrigation at the middle vegetative growth period (jointing), the late vegetative period (booting), the early reproductive period (heading), and the late reproductive periods (the end of filling or filling and maturity) could result in high grain yield, total biomass, water use efficiency, water supply use efficiency, harvest index, and better yield components in spring wheat in an arid environment. The optimum soil water deficit levels with highest grain yield, total biomass, water use efficiency, water supply use efficiency, harvest index and better yield components were proved to be 50–60, 65–70, 65–70, and 50–60% of field water capacity at the four growth stages above mentioned, with the corresponding optimum total irrigation water of 338 mm (averaged by present only two years of limited data in order to give a full consideration of the climatic variability) which was distributed as following: 75 mm during the middle vegetative stage (jointing), 90 mm during the late vegetative stage (booting), 68 mm during the early reproductive stage (heading), and 105 mm during the late reproductive stage (filling to maturity). Nevertheless, soil moisture contents were greatly decreased by regulated deficit irrigation during wheat growing seasons.
Acknowledgements This research was supported by NKBRSF Project of China (G2000018603) and Hundred-Talent Program project of CAS.
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