Maize yield response to deficit irrigation during low-sensitive growth stages and nitrogen rate under semi-arid climatic conditions

Agricultural Water Management 97 (2010) 12–22

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Maize yield response to deficit irrigation during low-sensitive growth stages and nitrogen rate under semi-arid climatic conditions Cyrus Mansouri-Far, Seyed Ali Mohammad Modarres Sanavy *, Seyed Farhad Saberali Department of Agronomy, Faculty of Agriculture, Tarbiat Modares University, P.O. Box 14115-336, Tehran, Iran

A R T I C L E I N F O

A B S T R A C T

Article history: Received 31 January 2009 Accepted 10 August 2009 Available online 23 September 2009

Knowledge of crop production in suboptimal environmental conditions not only helps to sustain crop production but also aids in the design of low-input systems. The objective of this study was to evaluate the effects of water stress imposed at low-sensitive growth stages (vegetative, reproductive, and both vegetative and reproductive) and level of nitrogen (N) supply (100 and 200 kg ha1) on the physiological and agronomic characteristics of two hybrids of maize (Zea mays L.). A two-site field experiment was carried out using a randomized complete block design with three replications and a split-factorial arrangement. A water deficit (WD) was induced by withholding irrigation at different stages of crop development. The results showed that proline content increased and the relative water content, leaf greenness, 100-kernel weight and grain yield decreased under conditions of WD. The highest IWUE was obtained when maize endured WD at vegetative stage at two sites. The limited irrigation imposed on maize during reproductive stage resulted in more yield reduction than that during vegetative stage, compared with fully irrigated treatment. The 100-kernel weight was the most sensitive yield component to determine the yield variation in maize plant when the WD treatments were imposed in low-sensitive growth stages. The results of the statistical regression analysis showed liner relationships between RGR during a period bracketing the V8 or R3 stages and 100-kernel weight in all the WD treatments. The increase of N supply improved yield and IWUE when maize plant endured once irrigation shortage at vegetative stage. But, the performance of high N fertilizer reduced and eliminated when water deficit imposed once at reproductive stage and twice at vegetative and reproductive stages, respectively. Furthermore, the response of T.C647 hybrid to increase of N supply was stronger than S.C647 hybrid. ß 2009 Elsevier B.V. All rights reserved.

Keywords: Maize Water deficit Irrigation water use efficiency Nitrogen Leaf greenness Leaf area index

1. Introduction Crop production during the summer months in the semi-arid environment of the Mediterranean regions relies on irrigation. River intakes and aquifers are the main sources of water supply for Iranian farms. The limited water resources in the area and the cost of pumping irrigation water are the most important factors that force many farmers to reduce irrigation in many arid and semi-arid regions of the Islamic Republic of Iran. The supply of nitrogen (N) is also important for crop production as much as water. Indiscriminate use of nitrogen leads to increase in production costs and environmental contamination (Meisinger and Randall, 1991; Burkart and Kolpin, 1993). Effective management strategies are desired that minimize input costs and environmental damage under suboptimal environmental conditions, but without sacrifice of crop performance or restriction of economic returns.

* Corresponding author. Tel.: +98 21 44196523; fax: +98 21 44196524. E-mail address: [email protected] (S.A.M. Modarres Sanavy). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.08.003

Conditions of water and N deficit lead to reductions in crop production by reducing resource capture and resource use efficiency. For example, WD induces a reduction in water potential, leaf elongation, leaf photosynthesis and N metabolism (Bogoslavsky and Neumann, 1998; Shangguan et al., 2000; Saneoka et al., 2004). In addition, the level of N supply affects the leaf area index (LAI), leaf area duration (Muchow, 1988; Uhart and Andrade, 1995), chlorophyll content and Rubisco activity (Evans and Terashima, 1987; Ding et al., 2005). Furthermore, an interaction between N and water supply has been demonstrated previously (Pandey et al., 2000a; Shangguan et al., 2000; Moser et al., 2006). Ercoli et al. (2008) showed that water supply influenced N uptake from the soil. It has been reported that maize grown under conditions of limited water supply requires less N to achieve the maximum grain yield than that required with well water supply (Moser et al., 2006). In maize, the reduction in grain yield caused by drought ranges from 10 to 76%, depending on the severity of the drought and the growth stage at which it occurs (Bolao`os et al., 1993). It has been reported that maize is relatively insensitive to water stress imposed during early vegetative growth stages because

C. Mansouri-Far et al. / Agricultural Water Management 97 (2010) 12–22 Table 1 Characteristics of soil in the two experimental fields. Characteristic

Depth (cm) EC (ds m1) pH (H2O) Organic matter (%) Total nitrogen (%) Extractable P (ppm) Extractable K2O (ppm) Field capacity water content (0.03 MPa) (%) Permanent wilting point water content (1.5 MPa) (%)

13

responses of two Iranian maize hybrids to water deficit at lowsensitive growth stages, and to evaluate the yield and IWUE of the hybrids under low water and N supply production systems.

Location Tehran

Kermanshah

0–140 1.3 7.74 0.10 0.068 30.40 452 16.3 8.9

0–100 0.83 7.7 0.26 0.128 21.20 2112 32.1 19.5

water demand is relatively low at this point, and the plants are able to adapt to water stress to reduce the effect of subsequent periods of water stress (Shaw, 1977; C¸akir, 2004). Doorenbos and Kassam (1979) have reported that maize appears to be relatively tolerant to water deficits imposed during the vegetative and ripening periods. Igbadun et al. (2007) suggested that good yields can be obtained with regular irrigation at the flowering growth stage, even if irrigation is limited during the vegetative and grain-filling stages. The yield potential of maize is, however, reduced by moisture stress that occurs just before anthesis (NeSmith and Ritchie, 1992), and during silking and seed fill (C¸akir, 2004; Musick and Dusek, 1980). Moser et al. (2006) have found that maize grown on moist soils requires more N to achieve the maximum grain yield than maize produced under conditions of moisture stress. Pandey et al. (2000a) have reported that the greater the N supply, the more the yield is reduced by deficient irrigation. Genetic characteristics can interact with environmental stress factors to affect maize growth and yield. Moser et al. (2006) have demonstrated that individual maize hybrids can respond differently to different water regimes. With regard to management of plants under conditions of water and N deficiency, future maize breeding efforts should focus on improving the tolerance of maize to water and N stresses. Characterization of the agronomic and physiological responses of different maize hybrids to water and N stresses could help to stabilize production at present levels, and to identify appropriate stress tolerance mechanisms for use in future maize breeding efforts. One of the best management approaches to maintenance of crop production during dry years depends on scheduling irrigation for available water supply and choosing drought-tolerant varieties or hybrids. The hypothesis of the study was that maize hybrids under water limited at low-sensitive growth stages would give similar response to level of N fertilization in the areas of study. To this end, the field experiments were performed to determine the agronomic and physiological

2. Materials and methods The field experiments were carried out in 2003 at the experimental farms of Tarbiat Modares and Razi Universities. The farms are located in Tehran (Iran) at 358410 N latitude, 518190 E longitude, 1190.8 m a.s.l., and in Kermanshah (Iran) at 348170 N latitude, 47870 E longitude, 30 m a.s.l. The soil types in Tehran and Kermanshah are fine sandy loam and clay, respectively. Table 1 shows other characteristics of soils in the two experimental sites. Annual rainfall (30-year-long term period) is mostly concentrated during the autumn and winter months at both sites (Fig. 1). The yearly average precipitation was 298 mm for Tehran and 424.2 mm for Kermanshah. The mean annual temperature was 18.8 8C for Tehran and 13.7 8C for Kermanshah. The monthly average precipitation and temperature at each site in 2003 is displayed in Fig. 1. The total open pan evaporation from sowing to maturity was about 1078 and 890 mm for Tehran and Kermanshah, respectively. The experiment involved a split-plot factorial design with three replications. Each replication was divided into four main plots, which differed in the stage at which water shortage was imposed. The four factorial combinations of N supply and maize hybrid (H) were randomly distributed within the sub-plots in each of the drought stress treatments (main plots). Four WD treatments were imposed by withholding irrigation at the eight-leaf (V8) stage (WDV), the early grain-fill (R3) stage (WDR), and at both V8 and R3 stages (WDVR); and a well-irrigated (WI) treatment was used as a control. Factorial combinations consisted of two levels of N fertilizer, 100 kg ha1 (N100) and 200 kg ha1 (N200), and two maize hybrids, single cross 647 (S.C647) and triple cross 647 (T.C647). Nitrogen fertilizer was used based on the local recommended application (200 kg ha1), with a grain yield forecast of about 900 g m2, and 1/2 recommended rate (100 kg ha1). The amount of required irrigation water was determined by Class ‘‘A pan’’ evaporation every day. The total evaporation from Class ‘‘A pan’’ was measured with a manual limnimeter which has 0.1 mm accuracy. A water flow meter, one for each irrigation treatment, was placed at the head of the experimental field to measure the amount of irrigation water applied accurately. Soil moisture characteristic curves (Fig. 2) were determined at each site using the method of Klute (1998). Four soil core samples were taken at rooting depths, between the 0–140 cm for Tehran and 0–100 cm for Kermanshah at 20 cm intervals, from the top of the ridge in each subplot. The samples were mixed, and then five

Fig. 1. Monthly precipitation and air temperature during the period January–December for 2003 and the long term (1971–2001) at Tehran and Kermanshah, Iran.

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C. Mansouri-Far et al. / Agricultural Water Management 97 (2010) 12–22

subsamples in 3% (w/v) sulphosalicylic acid with quartz sand at 4 8C. After centrifugation of the samples at 500  g for 10 min at 4 8C, the level of proline was quantified in the supernatant as described by Bates et al. (1973). The relative water content (RWC) of fully expanded last leaves was measured at the end of the stress period using the method of Weatherley and Barrs (1965). RWC was calculated using the following formula: RWC ¼

Fig. 2. Soil moisture characteristic curves for Tehran (fine sandy loam) and Kermanshah (Clay), Iran.

subsamples were placed within pressure plates apparatus at pressures of 0.01, 0.03, 0.1, 0.3, 0.5, 1 and 1.5 MPa. When moisture had been depleted from a soil sample at a given pressure, the sample was removed from the apparatus, weighed, dried at 105 8C for 48 h, and then weighed again to determine the moisture content. A non-linear inverse second-order polynomial curve was fitted to the resulting data. This curve was used to estimate the soil water potential of each soil sampling series, which was taken during the desired growth stage to impose water stress treatments. The soil depth of 1 m, for Kermanshah, was justified by the presence of a compact clay layer, which does not permit root penetration and water uptake. The maximum depth of 1.40 m, for Tehran, was considered as it was expected to be the maximum depth from which the maize would extract water. This assumption was supported by previous examinations of rooting depth under WD treatment at this location. The time of irrigation application was scheduled using the available soil water content at maximum rooting depth in each location. The available soil water at a rooting depth was determined as the difference between field capacity (0.03 MPa) and wilting point. The soil was irrigated when 45% of the available soil water was depleted. For the water deficit treatments, irrigation was withheld at the desired maize growth stages. The soil was irrigated before the soil water potential reached the permanent wilting point (approximately 1.4 MPa). The time periods between irrigation being withheld and the plants being re-watered were 8 and 17 days at the V8 stage, and 7 and 15 days at the R3 stage in Tehran and Kermanshah, respectively. Each subplot comprised six rows, 8 m long with spacing of 0.75 m between rows and 0.2 m within rows, at both sites. In order to prevent the lateral spread of water, plots were surrounded with dykes, and a 2-m wide strip was left bare between plots. Maize hybrids, FAO class 600, were sown on 18 and 28 May and harvested on 20 and 31 September 2003 at the Tehran and Kermanshah sites, respectively. The plant population density was 70,000 plants ha1 for both hybrids and at both sites. Triple super phosphate fertilizer was applied broadcast before sowing at a rate of 150 kg ha1. The N fertilizer, in the form of urea, was applied at planting (one-third of the application) and side-dressed at the V6 growth stage (twothirds of the application). Chlorophyll meter readings (SPAD) were collected at each site using a Minolta SPAD 502 meter at the end of the stress period. Measurements were taken midway along the uppermost collared leaf from six representative plants at the centre of two rows (rows 2 and 5) within each plot. Proline was extracted from frozen leaf

fresh weight  dry weight  100 saturated weight  dry weight

Four representative plants per plot were sampled at the desired stages and brought to the laboratory, where the leaves, stems, and inflorescences were separated and the green leaf area was measured using a leaf area meter (Area Measurement System, DELTA-T, Cambridge, UK). After the maize reached physiological maturity (R6), a 6.0-m stretch of plants from two adjacent rows (rows 3 and 4) were hand-harvested from each plot. All ears were harvested, the ears were dried at 75 8C, and then the grains were manually removed from the cobs. The dry grain was weighed, and yields were calculated on a 14% moisture content, wet basis. Irrigation water use efficiency (IWUE), defined as kilograms of grain per hectare produced per millimeter of growing season irrigation water applied. The data were analyzed by analysis of variance using the general linear model procedure in the Statistical Analysis System (SAS Institute, 2003). The UNIVARIATE procedure within SAS was used to examine the residuals for normality and to check for outliers in the data. In addition, the REG procedure was used to perform stepwise multiple regression analysis. Means were separated using Fisher’s protected least significance difference (LSD) test at the 95% level of probability. 3. Results and discussion 3.1. Proline and RWC The analysis of variance showed that the leaf RWC and proline status at the vegetative and reproductive stages were affected by water deficiency. However, the accumulation of proline and leaf RWC were not affected by N supply and hybrid. The proline status and RWC of leaves at the two locations were significantly different in the current study, but the interactions between treatments were not significant (Table 2). The difference in severity of stress that resulted from the different temperature (Fig. 1) and soil texture could explain this difference between the two locations. It appears that the severity of water stress was greater at the Tehran site, because the lighter soil texture and higher temperature led to faster discharge of soil available water than at Kermanshah. Therefore, the maize plant had less time to physiological response for drought stress, at Tehran. The comparison of means showed that the level of free proline and RWC of leaves at the V8 and R3 stages were significantly increased and decreased in response to WD treatments, respectively (Table 2). The increase of proline concentration in response to WD is a well documented phenomenon (Yeo, 1998; Monreal et al., 2007). A decline in leaf RWC during conditions of water stress has been reported for many plant species (Kerepesi and Galiba, 2000; Gubisˇ et al., 2007). 3.2. Leaf greenness (SPAD) WD and N treatments, as well as the interaction of WD  N, had significant effects on chlorophyll content at the V8 stage. At the R3 stage, a significant effect on chlorophyll content was found not only for the main effects of WD, N and H treatments, but also for all two-way and three-way interactions among WD, N and H

C. Mansouri-Far et al. / Agricultural Water Management 97 (2010) 12–22

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Table 2 Maize leaf proline, RWC and chlorophyll means and statistical groupings for main effect of water deficit and ANOVA significance levels. Site

Irrigation

ProlineVa (mmol fw g1)

ProlineRb (mmol fw g1)

RWCV (%)

RWCR (%)

SPADV

SPADR

Tehran

WDV WDR WDVR WI

20.86a 5.28b 16.45a 6.50b

3.80b 10.19a 14.09a 3.18b

72.61b 87.25a 71.76b 88.09a

87.41a 72.14b 71.95b 86.15a

43.66b 46.63a 43.21b 46.94a

37.12a 30.18b 29.94b 38.47a

Kermanshah

WDV WDR WDVR WI

19.82a 4.38b 16.63a 5.30b

3.54b 9.91a 13.75a 2.98b

78.11b 90.71a 76.85b 89.25a

88.94a 75.68b 74.92b 89.51a

45.46b 49.11a 44.22b 49.74a

43.99a 37.83b 38.00b 44.13a

Site means

WDV WDR WDVR WI

20.34 4.83 16.54 5.9

3.67 10.05 13.92 3.08

75.36 88.98 74.30 88.67

88.17 73.91 73.43 87.83

44.56 47.87 43.71 48.34

40.555 34.005 33.97 41.3

Source of variation Location (L) Rep E1 Water deficit (WD) WD  L E2 Nitrogen (N) Hybrid (H) WD  N WD  H NH NL HL WD  N  H WD  N  L NHL WD  H  L WD  N  H  L

df 1 2 2 3 3 12 1 1 3 3 1 1 1 3 3 1 3 3

*

*

**

*

**

*

**

*** **

** ***

***

***

***

***

*** ***

**

*** ***

*** ***

** *

* *** * ***

* ** * ***

Means within each column followed by the same letter are not statistically different at a = 0.05 by LSD test. a The V8 stage. b The R3 stage. *** Significance at P level of 0.001. ** Significance at P level of 0.01. * Significance at P level of 0.05.

treatments (Table 2). A significant effect of nitrogen and water stress on leaf chlorophyll has been reported previously (Brevedan and Egli, 2003; Dordas and Sioulas, 2008). The significant difference in leaf greenness of maize hybrids was probably due to different leaf N content of maize hybrids. Uribelarrea et al. (2007) found that plant N accumulation and N uptake efficiency were markedly affected by both the hybrid and by the N rate. The effect of site on leaf chlorophyll content was also significant (Table 2). The difference in soil texture between the two locations may have resulted in different levels of N loss and ultimately N availability. Endelman et al. (1974) have reported that as little as 2.54 cm of irrigation or rainfall can move soil N (NO3) 15–20 cm in a loamy sand soil. At both locations, leaf chlorophyll content was reduced by imposing a water deficit at the V8 and R3 stages. The mean values across the two sites showed that maize leaf greenness reduced 8–10 and 18% by water shortage at vegetative and reproductive stages, respectively (Table 2). In agreement with our results, Brevedan and Egli (2003) have demonstrated that chlorophyll content is reduced by water deficiency. In contrast, Teixeira and Pereira (2007) have reported that leaf chlorophyll content increases significantly in response to drought and decreases significantly in response to salinity. At the V8 stage, there was no significant difference in leaf greenness of the maize hybrids at either location, when grown under WDV treatment at both level of N application. In addition, an increased N supply did not affect the chlorophyll content significantly at the V8 stage in maize hybrids at either site (Table 4). The reduction in N uptake caused by imposition of an irrigation deficit (Ercoli et al.,

2008), led to a reduction in the effect of high N supply on chlorophyll content. At the Tehran site, chlorophyll level at the R3 stage in plants under WDV treatment with high N supply was greater than that of plants with low N supply. Moreover, the chlorophyll concentration in the T.C647 hybrid was significantly greater than that of the S.C647 hybrid under high N supply. At Kermanshah, the leaf greenness of T.C647 at the R3 stage was greater than that of S.C647, at both levels of N supply. Furthermore, the amount of leaf chlorophyll in the similar hybrid did not differ with N supply (Table 4). High N level resulted in increased leaf greenness of maize hybrids at the reproductive stage at the Tehran site only, where leaching of N was much greater than at Kermanshah. At both locations, maize hybrids grown under WDR treatment at the V8 stage showed no significant differences in leaf greenness at a particular N level. However, the chlorophyll content in each hybrid increased significantly with increasing N supply. At the Tehran site, there was no significant difference in chlorophyll concentration at the R3 stage between the maize hybrids, at the same level of N (Table 4). At the Kermanshah site, the chlorophyll content of the T.C647 hybrid at the R3 stage, under conditions of high N supply, was greater than that of the S.C647 hybrid. At a low level of N application, there were no significant differences in chlorophyll content between the two hybrids. Moreover, the higher N application resulted in increased leaf greenness only in T.C647 (Table 4). In contrast to the WDV treatment, maize grown under WDR treatment and higher N supply showed improved leaf greenness at the vegetative stage (Table 4). This may be attributed to adequate N uptake during the vegetative stage under unstressed

C. Mansouri-Far et al. / Agricultural Water Management 97 (2010) 12–22

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in more leaf greenness in maize hybrids. At the Tehran site, there was no significant difference in chlorophyll content between the R3 stage hybrids maintained at a high level of N supply. However, the T.C647 hybrid had higher chlorophyll content than S.C647 when grown with a low level of N supply. At Kermanshah, there was no significant difference in chlorophyll concentration between the two R3 stage hybrids, at a given level of N supply. Increased leaf greenness with enhanced N supply was significant only at the Tehran site. It has been found that, when there is an adequate supply of N in the soil, leaf senescence is slower and the plant is able to supply its seeds with N and to photoassimilate for a longer period, which results in higher yields (Eghball and Power, 1999).

conditions. Hoeft et al. (2000) have found that 60% of the total N uptake by maize has occurred by the time of tasseling. The maize hybrids at both sites showed no significant difference in leaf greenness at the V8 stage, at a given level of N supply, when grown under WDVR treatment conditions. The leaf greenness in each hybrid at this stage was also not affected by the level of N supply (Table 4). At the R3 stage, leaf greenness in the T.C647 hybrid was significantly higher than that of S.C647 for both N100 and N200 treatments, at the two locations. Furthermore, the leaf greenness in each hybrid increased significantly with increased N supply (Table 4). The improvement of leaf greenness was greater at the R3 stage than V8 stage with increased N supply, when the water deficit was imposed at both vegetative and reproductive stages. In addition, leaf greenness of the T.C647 hybrid at the R3 stage was greater than that of S.C647, at both levels of N supply. Ding et al. (2005) have reported that accelerated loss of chlorophyll (senescence) caused by N deficiency has different intensity in maize hybrids after anthesis. The ‘stay-green’ trait is a component of tolerance of terminal drought stress in cereals such as maize (Campos et al., 2004). It was found that high leaf N during reproductive stage allowed stay-green genotypes to continue photosynthesis and N uptake under drought stress while senescent genotypes had to rely on N and photosynthate translocated from the leaves and other tissues (Borrell and Hammer, 2000; Spano et al., 2003). At both sites, the maize hybrids, grown under WI, showed no significant differences in chlorophyll content at the V8 stage and a given level of N supply. At this stage, the higher N supply resulted

3.3. LAI The analysis of variance showed that the WD, N and H treatments had significant effects on maize LAI at the V8 stage. In contrast, at the R3 stage, only the main effect of nitrogen was significant (Table 3). N supply affected LAI during vegetative and reproductive stages by leaf elongation and leaf senescence, respectively (Uhart and Andrade, 1995; Muchow, 1988). The comparison of means showed no significant difference in LAI at the R3 stage among water supply treatments at both sites. However, the LAI was significantly reduced when the water deficit occurred at the V8 stage (WDV and WDVR treatments). The LAI means for 2 sites showed that LAI under WD treatments was reduced by about 15 and 3–4% compared with the WI treatment at vegetative and reproductive stage, respectively (Table 3). The results showed that

Table 3 Maize LAI, 100-Kernel weight, grain yield and IWUE means and statistical groupings for main effect of water deficit and ANOVA significance levels. Site

Irrigation

LAIVa (m2 m2)

Tehran

WDV WDR WDVR WI

1.46b 1.61a 1.43b 1.62a

Kermanshah

WDV WDR WDVR WI

Site means

WDV WDR WDVR WI

Source of variation Location (L) Rep E1 Water deficit (WD) WD  L E2 Nitrogen (N) Hybrid (H) WD  N WD  H NH NL HL WD  N  H WD  N  L NHL WD  H  L WD  N  H  L

df 1 2 2 3 3 12 1 1 3 3 1 1 1 3 3 1 3 3

LAIRb (m2 m2)

100-kernel weight

Grain yield (kg ha1)

IWUE (kg ha1 mm1)

2.87a 2.89a 2.78a 2.80a

22.8a 19.00b 21.8a 22.3a

8177.2a 6743.0b 6491.0b 8701.8a

11.52a 9.66b 9.95b 11.68a

1.06b 1.21a 1.09b 1.33a

3.47a 3.78a 3.67a 3.82a

26.5a 25.9a 25.8a 26.9a

8244.2b 7208.6c 7033.7c 9307.3a

12.28ab 10.94b 11.09b 13.37a

1.26 1.41 1.26 1.475

3.17 3.33 3.225 3.31

24.65 22.45 23.8 24.6

8210.7 6975.8 6762.35 9004.55

11.9 10.3 10.52 12.525

*

* *

**

***

**

**

*

*

**

*

***

***

*

*

*

*

*

*

***

**

***

RGRR

**

***

**

*

RGRv

**

*

**

*

** **

*

*

**

**

*

*

**

**

**

**

*

* *

Means within each column followed by the same letter are not statistically different at a = 0.05 by LSD test. a The V8 stage. b The R3 stage. *** Significance at P level of 0.001. ** Significance at P level of 0.01. * Significance at P level of 0.05.

C. Mansouri-Far et al. / Agricultural Water Management 97 (2010) 12–22

LAI decreased as a result of water deficit imposed at the V8 stage, but this reduction was compensated at the R3 stage. This shows that maize is able to recover from water stress that occurs once at the vegetative stage. Sanchez-Diaz and Kramer (1971) have demonstrated the ability of maize to recover following rewatering, when stress ceases. Bogoslavsky and Neumann (1998) have reported that among the growth processes of plant leaf elongation is the most sensitive to water shortage. The decrease in LAI of the maize plant exposed to water stress at the vegetative stage has been reported previously (C¸akir, 2004). In contrast, Pandey et al. (2000b) have reported that water deficit both at the vegetative and reproductive stages decreases LAI in maize. At both sites, there was no significant difference in LAI between the maize hybrids with a given N application rate (Table 4). The level of N supply had no significant effect on LAI at the V8 stage in maize hybrids grown under WDV treatment. The same trend in LAI was seen at the R3 stage at Kermanshah. However, at the Tehran site, the LAI in the S.C647 hybrid was significantly greater with the high level of N supply (Table 4). It appears that the lower N supply was adequate to allow the plants to reach maximum LAI when the maize endured a water deficit at the V8 stage, with the exception of S.C647 when grown in a sandy-textured soil. Prasertsak and Fukai (1997) reported that there was no significant effect of N on LAI when rice was grown under conditions of stress. At the Tehran site, LAI in maize hybrids at the V8 stage under WDR treatment was significantly diminished with low N application than that of high N application. In contrast, at the R3 stage, there was no significant difference in the LAI of the given hybrids at the two levels of N supply (Table 4). At Kermanshah, the LAI of maize hybrids at the V8 and R3 stages was not affected by changes in N supply when grown under WDR treatment. The difference in responses to N supply

17

between locations was probably related to differences in the amount of N loss through leaching. Moreover, the maize hybrids maintained at the same rate of N application showed no significant differences in LAI, at two locations. In the clay soil at Kermanshah, the higher N application had no significant effect on LAI when maize hybrids were grown under WDVR treatment. At Tehran, the LAI at the V8 stage followed the same trend, but the LAI at the R3 stage was significantly higher in plants given the N200 treatment. The maize hybrids showed no significant difference in LAI at a given level of N application (Table 4). At the Tehran site, enhancement of the N supply under well-irrigated conditions led to an increase in LAI at the V8 and R3 stages. In contrast, at Kermanshah, there was no significant difference in LAI between plants given the two levels of N supply under well-irrigated conditions (Table 4). Generally, LAI was improved by the higher N supply when maize hybrids were grown on soil of lighter texture. In contrast, the N100 treatment was sufficient for production of maximum LAI in plants grown on a clay soil. At both locations, the two maize hybrids showed no significant difference in LAI at a given level of N supply, under both well-irrigated and water-deficient conditions. It has also been shown that maize responds to N stress by maintaining resource capture (leaf size) at the expense of resource use efficiency (Vos et al., 2005). Subedi et al. (2006) found that different N rates (75 and 150 kg ha1) had no significant effect on LAI in maize plant under well-irrigated condition. 4. Grain yield The main effects of irrigation, nitrogen and hybrid on grain yield were significant. In addition, the two-way interaction of WD  N

Table 4 Treatment means and statistical groupings for the N  hybrid interaction at any level of water deficit treatment.

Tehran

Irrigation

Nitrogen

Hybrid

SPADVa

SPADRb

LAIV (m2 m2)

LAIR (m2 m2)

Yield (kg ha1)

IWUE (kg ha1 mm1)

WDV

N200

S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647

44.07a 44.17a 41.77a 44.63a 50.23a 48.53ab 45.03bc 42.73c 45.60a 42.87a 41.03a 43.33a 49.20a 50.23a 44.40b 43.93b

38.40b 42.60a 35.77c 35.70c 32.17ab 33.70a 26.37c 28.50bc 30.63b 33.47a 26.80d 28.87c 37.90a 37.07a 29.67c 33.27b

1.47a 1.71a 1.40a 1.31a 1.90a 1.77a 1.36b 1.35b 1.37a 1.57a 1.47a 1.32a 1.83a 1.86a 1.39b 1.41b

3.06a 3.07a 2.52b 2.83ab 3.04a 3.12a 2.67a 2.72a 3.08a 3.00a 2.62b 2.47b 3.07a 3.11a 2.58b 2.45b

8440.43ab 9225.07a 7861.77b 8081.57b 6293.97a 7441.93a 5986.13a 7250.00a 6016.17b 7314.13a 6091.17b 6542.6ab 8598.57b 9886.13a 8027.00b 8205.37b

11.88ab 12.99a 11.073b 11.28b 9.02ab 10.66a 8.57b 10.38ab 9.74ab 11.03a 9.18b 9.86ab 11.54b 13.27a 10.77b 11.01b

S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647 S.C647 T.C647

46.57a 45.73a 44.77a 44.77a 52.50a 51.03a 47.13b 45.77b 46.10a 45.23ab 43.33ab 42.20b 51.93a 52.30a 48.07b 46.67b

40.60b 44.50a 39.93b 45.87a 36.50b 42.93a 36.60b 35.67b 44.40b 48.30a 39.57c 43.70b 44.33ab 46.73a 42.00b 43.06ab

1.25a 0.99a 1.11a 0.92a 1.29a 1.14a 1.15a 1.23a 1.07a 1.18a 1.23a 0.96a 1.40a 1.42a 1.30a 1.17a

3.63a 3.48a 3.53a 3.23a 3.90a 3.80a 3.78a 3.67a 3.65a 3.92a 3.53a 3.57a 3.93a 3.98a 3.76a 3.61a

8467.33b 9416.33a 7271.33c 7821.67cb 7236.67ab 8489.33a 6322.67b 6785.67b 7272.67ab 7702.50a 6393.67b 6766.00ab 9515.00a 9820.33a 8809.00a 9089.00a

12.62ab 14.03a 10.84c 11.65cb 10.98b 12.8a 9.59b 10.29b 11.47ab 12.15a 10.084b 10.67ab 13.67a 14.11a 12.65a 13.58a

N100 WDR

N200 N100

WDVR

N200 N100

WI

N200 N100

Kermanshah

WDV

N200 N100

WDR

N200 N100

WDVR

N200 N100

WI

N200 N100

Means within each column followed by the same letter are not statistically different at a = 0.05 by LSD test. a The V8 stage. b The R3 stage.

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and the three-way interaction of WD  N  H were significant (Table 3). Furthermore, the effect of location was significant on grain yield because of the significant differences in leaf greenness and LAI of maize plant between locations. At the Tehran site, grain yield under the WDV, WDR and WDVR treatments was reduced by about 6.0, 22.5 and 25%, respectively compared with the control (WI), although the yield loss was significant only for the WDR and WDVR treatments. At Kermanshah, the reduction in yield with the WDV, WDR and WDVR treatments compared with the control was 11.0, 22.5 and 24.4%, respectively. The mean yield reduction with the WDV, WDR and WDVR treatments compared with the control was 9, 22.5 and 25%, respectively. The difference in grain yield between the WDR and WDVR treatments was not significant at either location (Table 3). Pandey et al. (2000b) have reported that maize plants under vegetative water stress utilized an adaptive strategy that involved extension of the root depth and increased water extraction from the deeper soil profile. The extended root depth within a light soil could explain the reduced loss of yield under vegetative water stress applied once at the Tehran site. A decrease in root permeability may be caused by higher bulk density and creation of anaerobic conditions at the lower layer, as previously reported (Bandyopadhyay and Mallick, 2000; Kar and Verma, 2005). In Washington, Robins and Domingo (1953) found that soil water depletion to the wilting percentage for 1–2 days at the tassel or pollination stage reduced yield by 22%, and if it was applied for 6–8 days, yield was reduced by 50%. At the Tehran site, the two maize hybrids grown under WDV treatment showed no significant difference in grain yield at a given level of N application. The yield was enhanced 6.8 and 12.4% in S.C647 and T.C647 hybrids, respectively, with increased N supply. However, the increase in yield was significant only in T.C647 (Table 4). Under the same conditions at Kermanshah, the grain yield in the T.C647 hybrid was significantly greater than that of S.C647 at the high rate of N application. In contrast, there was no significant difference between the two hybrids under the low N supply. Moreover, the higher level of N supply resulted in a significant increase in yield of about 14.0 and 17.0% in S.C647 and T.C647, respectively (Table 4). At both locations, the grain yield of T.C647 was slightly more than that of S.C647 for both N100 and N200 treatments, when the maize hybrids were grown under WDR treatment conditions, but this difference was not statistically significant. At the Tehran site, a higher N supply led to a nonsignificant increase in yield of about 5 and 3% in S.C647 and T.C647, respectively. At Kermanshah, the increased rate of N application led to an enhancement in yield of about 12.6 and 20.1% in S.C647 and T.C.647, respectively, but only the increase for T.C647 was significant (Table 4). At the Tehran site, when water shortage was imposed twice (at the V8 and R3 stages), the grain yield of T.C647 at the high and low N rate was about 18 and 7% higher than that of S.C647. This difference between hybrids was not significant at the low level of N supply. At Kermanshah, there was no significant difference between the two hybrids when grown under WDVR treatment at either level of N supply. Also, changing the level of N supply did not have a significant effect on the grain yield of either hybrid at the two locations (Table 4). The maize hybrids grown under wellirrigated conditions at the low rate of N application showed no significant difference in yield. However, at the high level of N supply, the yield of T.C647 was 13.0% more than that of S.C647, at Tehran site. The increased application of N resulted in yield enhancements of 4.6 and 18.8% in S.C647 and T.C.647, respectively, but the increase was only significant in T.C647. At Kermanshah, the yield of the maize hybrids under WI treatment conditions showed no significant differences at either level of N supply. The increased yield with increasing N supply was not significant for either hybrid (Table 4).

It was found that the economically optimum rate of N required for maize may vary spatially due to variation in soil characteristics and temporally due to the interactions of environmental factors (Mamo et al., 2003; Katsvario et al., 2003). In general, the maize hybrids in conditions of low N supply showed no significant difference in grain yield when they were grown under stressed and unstressed conditions. But, the T.C647 hybrid showed better performance than S.C647 hybrid under high N supply in some experimental conditions. The greater leaf greenness of T.C647 compared with that of S.C647, especially in response to high N supply, can be the reason of satisfactory performance in T.C647. Uribelarrea et al. (2007) found that plant N accumulation and N uptake efficiency were markedly affected by both the hybrid and by the N rate. Moll et al. (1982) evaluated some single cross hybrids under low N and high N levels and attributed genetic differences in grain yield under low N to differences in N utilization. Under high N, they attributed genetic differences in grain yield largely to variation in N uptake. Stay-green genotypes have a greater capacity to take up N during grain-fill because continued leaf activity promotes the uptake of soil N (Woodruff, 1972). Roots need a supply of photosynthate to absorb soil N, so late season photosynthesis helps maintain N uptake after anthesis. Furthermore, it found that among WD treatments increased N rate was the most efficiency when maize hybrids endured once water stress during vegetative stage. Moreover, increased N under WDR treatment was more performance than WDVR treatment. It seems N shortage was an essential factor for yield reduction under water deficit, especially when it occurred during reproductive stages. Worku et al. (2007) reported that N uptake between anthesis and physiological maturity was more important than N uptake before anthesis for increased grain yields. The reduction in radiation use efficiency (RUE) and the consequences for grain yield was reported under water and N deficit (Muchow and Sinclair, 1991; Muchow and Davis, 1988). 4.1. Grain yield determination The analysis of variance showed that the 100-kernel weight was the most important yield component to determine the yield variation in WD treatments. Moreover, it explained yield variation between two hybrids (Table 2). Sadras (2007) reported that the variation in seed size of maize and sunflower is large and comparable to the variation in seed number, in comparison to crops like wheat or soybean where seed numbers allow greater responsiveness to resource availability. Drought stress reduced the capacity of assimilate production due to a small green leaf area and leaf greenness. Thus, reduced current and reserve carbohydrates production during reproductive and/or vegetative water deficit may have limited the 100-kernel weight in our study. Regression analysis also confirmed that 47–86% of the total variation in grain yield of maize hybrids could be explained by the variation in LAI and leaf greenness following the WDV, WDR, WDVR and WI treatments (Table 5). LAI at the vegetative stage was the most component to explain yield variation in WDV and WI treatments, but leaf greenness at the reproductive stage had the same role when maize plants endured WDR and WDVR treatments (Table 5). Moreover, the importance of LAI and leaf greenness to explain the variations was dependent on hybrid types and development stages at which maize hybrid endure water deficit. Indeed, LAI and leaf greenness determine the capture and use of solar radiation by maize plant, hereby they affected the conversion rate of available radiation to dry matter accumulation. Tollenaar et al. (2004) found that increased LAI, stay-green and sustaining photosynthesis of green leaf area especially during the grain-filling period are the main physiological processes associated with Heterosis for grain yield in maize. In addition, it has been shown

C. Mansouri-Far et al. / Agricultural Water Management 97 (2010) 12–22

19

Table 5 Summary of stepwise multiple regression analysis in maize grain yield (as dependent variable) and chlorophyll and LAI at the V8 and R3 stages (as independent variables). Irrigation

Hybrid

Regression equation

R2

Significance level

WDV

S.C647 T.C647

Yield = 5124.56 + 2690.56LAIv Yield = 922.10 + 1698.79LAIv + 168.83SPADR

0.73 0.84

**

S.C647 T.C647

Yield = 754.01 + 174.38SPADR Yield = 301.50 + 222.67SPADR

0.48 0.66

*

S.C647 T.C647

Yield = 2900.26 + 109.23SPADR Yield = 5380.79 + 175.50SPADR  1609.48LAIR

0.47 0.75

*

S.C647 T.C647

Yield = 3167.15 + 2015.98LAIv + 815.03LAIR Yield = 1475.30 + 2705.10LAIv + 83.20SPADR

0.83 0.86

**

WDR

WDVR

WI

***

**

**

***

SPADR: SPAD at the R3 stage; LAIR: LAI at the R3 stage; LAIV: LAI at the V8 stage. *** Significance at P level of 0.001. ** Significance at P level of 0.01. * Significance at P level of 0.05.

that decreased leaf photosynthesis during the grain-filling period by abiotic stresses is greater in stress-susceptible than in stresstolerant hybrids (Tollenaar and Lee, 2002; Ying et al., 2002). The comparison between older and newer maize hybrids showed that selection for high yield potential is intimately linked to selection for stress resistance (Tollenaar and Lee, 2002). Relative growth rate (RGR) during a period bracketing the V8 or R3 stages, where maize hybrids subjected to water deficit, was significantly affected by WD treatments. Furthermore, a significant difference in RGR found between two hybrids at V8 stage (Table 3). The relationships between RGR and 100-kernel weight for the 2 sites of experiment are reported in Figs. 4 and 5. The results of the statistical regression analysis showed that liner relationships between given RGR and 100-kernel weight in all the WD treatments. The relationship between 100-kernel weight and RGR was stronger in T.C647 hybrids (R2 = 0.90) than S.C704 hybrid (R2 = 0.88) when WD treatment imposed at vegetative stage (Fig. 4). Furthermore, no significant difference was found between RGR of maize hybrids grown under WDR treatment; thus, the RGR data of two hybrids combined and a significant linear relation of 100-kernel weight to RGR found at reproductive stage (Fig. 4). The relationship between 100-kernel weights of two hybrids versus RGR at R3 stage was stronger than RGR at V8 stage, when water deficit imposed twice at vegetative and reproductive stages (Fig. 5). Jones et al. (1985, 1996) reported a highly positive correlation between kernel growth rate and number of endospermatic cells and starch granules, which in turn determine the potential kernel size. Variation in final grain weight was reflected the interaction between source capacity and sink strength (i.e. the source/sink ratio) during the effective grain-filling period (Westgate et al., 2004; Andrade et al., 2005). Source capacity is determined by the

current photosynthetic activity of the crop and by the availability of carbohydrate reserves (Westgate et al., 2004). Water deficiency due to reduce leaf area and greenness resulted in decreasing radiation interception and radiation use efficiency that is related directly to carbon assimilation and plant growth (Boyer, 1970; Tollenaar et al., 2004). This is probably the reason for the close relationship between kernel weight and relative growth rate. Based on these results, it can be inferred that differences in kernel weight of maize hybrids were associated with variations in RGR which determined the conversion rate of available resources (such as radiation) to dry matter accumulation. 4.2. Yield–irrigation relationship The linear relationship was found between yield and seasonal irrigation in any of the two study locations (Fig. 3). Payero et al. (2006) also reported that liner relationship between grain yield and seasonal water applied in maize subject to deficit irrigation treatments. However, it was reported that irrigation versus yield have been linear, curvilinear and no linear relationship (Tolk and Howell, 2003; Payero et al., 2006; Farre´ and Faci, 2009). It was found that the generalized relationship between irrigation water supply and yield when applied water are all initially consumed in ET producing a linear relationship with yield (Payero et al., 2008). Comparing the regression lines of two locations showed that higher slope of the regression line and the R2 value at Kermanshah, with clay soil, than that of location with sandy loam soil (Tehran). Low water holding capacity in sandy loam soil resulted in high water lose by percolation and ultimately reduction yield–irrigation relationship at Tehran sit. Payero et al. (2006) showed that the reported yield versus ET relationships for maize are not consistent

Fig. 3. Relationship between maize grain yield and seasonal irrigation amounts as a function of nitrogen treatments at Tehran (left) and Kermanshah (right), Iran.

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C. Mansouri-Far et al. / Agricultural Water Management 97 (2010) 12–22

Fig. 4. Relationship between relative growth rate (RGR) during a period bracketing V8 and R3 stages and 100-kernel weight for hybrids S.C647 (continuous line) and T.C647 (cut line) when maize plant endured once water deficit at V8 (left) or R3 (right) stages. The RGR data at R3 stage of 2 hybrids combined, because of no significant difference between hybrids.

and vary with location, which is likely due to differences in precipitations pattern, soil and crop characteristics and weather conditions. The slopes of the regression lines, which represent the increment of grain yield for unit increment of seasonal irrigation, were different between N treatments over the two locations. At Tehran, the linearity of the regression line for the N200 treatment was higher than that of N100 treatment. On the contrary, the linearity of the regression line for the N200 treatment was slightly lower than that of N100 treatment, at Kermanshah (Fig. 3). Di Paolo and Rinaldi (2008) showed the linearity of the regression line for the N300 was slightly higher than that of N150 treatment. 4.3. Irrigation water use efficiency (IWUE) The main effects of WD, N, H and the interaction of WD  N treatments on IWUE were significant (Table 3). The comparison of means between WD treatments showed that IWUE in WDV and WI treatments were more than WDR and WDVR treatments at Tehran. Moreover, at Kermanshah, WI treatment had the highest IWUE among WD treatments. However, no significant differences in IWUE values found not only in WDV, WDR and DWVR treatments, but also in WDV and WI treatments (Table 3). Thus, maize could endure at least once irrigation deficit during vegetative stage without sacrificing IWUE. Moreover, imposing water deficit twice; i.e. at the low-sensitive vegetative and reproductive stages had similar effect on IWUE compared to imposing water deficit at the

vegetative stage only. Arora and Gajri (1998) reported that in order to optimize crop yields and WUE in irrigated environments, irrigations should be timed in a way that possible inevitable water deficits coincide with least sensitive growth period. The proper water deficits in certain growth stages are helpful for increase of yield and WUE (Asseng et al., 1998). Although, inverse the previous studies, Payero et al. (2006) found no beneficial increase in WUE in the semi-arid environment of the US Great Plains with deficit irrigation. No significant differences in IWUE of maize hybrids found at the WDV treatment with similar N level, at the both locations. Moreover, the increases of N supply enhanced IWUE in T.C647 hybrid, at Tehran, but this increase was observed for both hybrids, at Kermanshah (Table 4). While, no significant differences in IWUE found between hybrids with similar N supply at Tehran, when maize hybrids endured WDR treatment, IWUE in T.C647 was more than S.C647 under high N supply, at Kermanshah. Moreover, the increase of N rate made only significant increase in IWUE of T.C647 hybrid at the Kermanshah location. When maize endured WDVR treatment, not only no significant differences found between hybrids with similar N supply, but also the increase of N supply had no significant increase on IWUE of hybrids, at both sites. The IWUE of T.C647 hybrid was enhanced by increase of N supply under well irrigation treatment, at Tehran. Furthermore, the differences between hybrids were significant under high N rate. But, increase of N rate and hybrid type made no significant differences in IWUE of maize plant imposed to WI treatment, at Kermanshah (Table 4).

Fig. 5. Relationship between relative growth rate (RGR) during a period bracketing V8 (cut line) and R3 (continuous line) stages and 100-kernel weight for hybrids S.C647 (left) and T.C647 (right), when maize plant endured twice water deficit at V8 and R3 stages.

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In general, it was found that the increase of N supply led to more IWUE when maize endured once water deficit at vegetative stage. Moreover, T.C647 hybrid was more efficient in using high level of N supply to output more IWUE. Some researchers reported that maize is particularly very sensitive to water and other environmental stresses (NeSmith and Ritchie, 1992; C¸akir, 2004; Pandey et al., 2000a,b). This high sensitivity to water stress means that under water deficit conditions, it is difficult to implement irrigation management strategies without incurring in important yield losses. However, the results showed that irrigation water can be conserved and yields maintained in maize plant (as sensitive crop to drought stress) under water limited conditions through improved fertilizer managements and selecting more tolerant hybrids. Di Paolo and Rinaldi (2008) carried out a 2-year field experiment in Italy in which corn was subjected to three irrigation levels (rainfed and supply at 50 and 100% of crop evapotranspiration) in interaction with three nitrogen fertilization levels. They found that nitrogen rates affected water use efficiency and irrigation water use efficiency, with significant differences between non-fertilized and the two fertilized treatments (15 and 30 g (N) m2). Halvorson et al. (2006) reported that water use efficiency can be increased by N application and WUE increased curvilinearly with increasing level of available N. 5. Conclusion Our results show that in both locations, water stress imposed on maize in three low-sensitive growth stages resulted in more yield reduction during R3 stage than V8 stage, compared with fully irrigated treatment. WD treatments significantly affected RWC, proline, LAI and leaf greenness of maize plant; but regression analysis showed that 47–86% of the total variation in grain yield of maize hybrids could be explained by the variation in LAI and leaf greenness. Moreover, T.C647 hybrid was observed to yield relatively well under both deficit and adequate water supply, suggesting that the agronomic and physiological characteristics associated to high yield potential could be used as stress tolerance indexes in future elite germplasm. The 100-kernel weight was the most important yield component to determine the yield variation in maize hybrids when imposed WD treatments in low-sensitive growth stages. Furthermore, it was found that the differences in kernel weight of maize hybrids were associated with variations in RGR. Thus, physiological features associated with ability to maintain 100-kernel weight under water stress in low-sensitive growth stages should be a high priority of maize improvement programs. The cut of once irrigation application at vegetative stage can be done without sacrificing IWUE. Furthermore, imposing water deficit twice; i.e. at the low-sensitive vegetative and reproductive stages had similar effect on IWUE compared to imposing water deficit at the vegetative stage only. Although, deficit irrigation reduced potential yield of maize plant in comparison to adequate water supply; however this practice led to the possibility of crop production with regard to conserving irrigation water, the reduction of irrigation application cost and sustainability of irrigated agriculture in arid and semi-arid regions. The increase of N supply could improve yield and IWUE when maize plant endured once water shortage at vegetative stage. But, the performance of high N fertilizer reduced and eliminated when water deficit imposed once at reproductive stage and twice at vegetative and reproductive stages, respectively. Furthermore, the response of T.C647 hybrid to increase of N supply was stronger than S.C647 hybrid. Thus, the improved fertilizer managements and selecting tolerant hybrids can increase the performance of deficit irrigation scheduling in semi-arid regions where water is the most limited resource to crop production.

21

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