Yield, water and nitrogen use efficiencies of sprinkler irrigated wheat grown under different irrigation and nitrogen levels in an arid region

Agricultural Water Management 187 (2017) 232–245

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Research Paper

Yield, water and nitrogen use efficiencies of sprinkler irrigated wheat grown under different irrigation and nitrogen levels in an arid region Vijay Singh Rathore a,∗ , Narayan Singh Nathawat a , Seema Bhardwaj a , Renjith Puthiyedathu Sasidharan a , Bhagirath Mal Yadav a , Mahesh Kumar b , Priyabrata Santra b , Narendra Dev Yadava a , Om Parkash Yadav b a b

ICAR- Central Arid Zone Research Institute, Regional Research Station, Bikaner, 334004, Rajasthan, India ICAR- Central Arid Zone Research Institute, Jodhpur, 342003, Rajasthan, India

a r t i c l e

i n f o

Article history: Received 10 December 2016 Received in revised form 25 March 2017 Accepted 28 March 2017 Keywords: Deficit irrigation Nitrogen use efficiency Triticum aestivum L. Water-nitrogen interaction Water productivity

a b s t r a c t A major challenge in crop production is to achieve the goal of increasing both yield and resource use efficiency. Irrigation water and nitrogen (N) are scarce and expensive resources constraining wheat production in arid regions. There is limited information on how irrigation and N supply can be simultaneously manipulated to achieve higher yield, water productivity (WP), and nitrogen use efficiency (NUE) of wheat in arid regions. A two-year field experiment was conducted to investigate the effects of irrigation and N rates on yield, WP and NUE of wheat in a hot, arid environment at Bikaner, India. The experimental treatments comprised of six irrigation [100% (ETm; full evapotranspiration), 90% (ETd1), 80% (ETd2), 70% (ETd3), 60% (ETd4), and 50% (ETd5) of ETc (crop evapotranspiration)] levels, and four N [0 (N0), 40 (N40), 80 (N80), and 120 (N120) kg ha−1 ] rates. Moderate deficit irrigation (ETd2) had greatest WP and caused a 17% reduction in water consumption with only a 5% reduction in yield compared to full irrigation (ETm). The N application improved yield and WP. The NUE declined with a reduction in water application and an increase in N rates. The yield and WP response to N rates modified with irrigation levels.The significant increase in grain yield was recorded with N120 at ETm and ETd1, with N80 at ETd2 and ETd3, and with N40 at ETd4 and ETd5 irrigation levels. The significant increase in WP was recorded with N80 at ETm, ETd1, ETd2 and ETd3, and with N40 at ETd4 and ETd5 irrigation levels. The results suggested that moderate deficit irrigation (ETd2) along with 120 kg N ha−1 could ensure satisfactory grain yield and WP of wheat in arid regions. The study also indicated that the adoption of an appropriate deficit irrigation and N rate combination can be an effective means to reduce non-beneficial water consumption, achieve higher yield, and improve WP and NUE for wheat in an arid environment. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Globally, agriculture uses almost 70% of all fresh water withdrawals for irrigation (Shen et al., 2008). Irrigated agriculture produces about 40% of all food from about 17% of the cropped land area (Fereres and Connor, 2004). Due to continued population growth, urbanization, and industrialization, agriculture will increasingly compete with other sectors for fresh water (Godfray et al., 2010; Tilman et al., 2011). The global demand for food crops is expected to approximately double by 2050 (Tilman et al., 2011). Therefore, crop production will need to increase to meet the projected demand for food, but the portion of fresh water available to

∗ Corresponding author. E-mail address: [email protected] (V.S. Rathore). http://dx.doi.org/10.1016/j.agwat.2017.03.031 0378-3774/© 2017 Elsevier B.V. All rights reserved.

agriculture is decreasing (Cai and Rosegrant, 2003). This highlights the challenges agriculture is faced with the need to grow more food with less water (Godfray et al., 2010). Hence, sustainable methods to increase crop water productivity (WP) are gaining importance, particularly in arid and semi-arid regions, where water remains a major production constraint. Wheat (Triticum aestivum L.) is one of the most important crops, providing over 20% of the calories consumed by the world’s population (Braun et al., 2010). It is an important crop in irrigated perimeters of the arid region of India (Gajja et al., 2008; Rathore et al., 2010), where it is grown during November to April. The precipitation ranges from 30 to 50 mm, while the average evaporation is 800–1000 mm during the wheat growing season. To achieve high yield, farmers in this region pump groundwater to irrigate wheat to offset the evapotranspiration (ET) deficit. The excessive exploitation of groundwater (which constitutes 52.3% share in the total

V.S. Rathore et al. / Agricultural Water Management 187 (2017) 232–245

irrigated area in northwestern Rajasthan) for irrigation is depleting at an alarming rate (Rathore, 2005), and is posing a serious threat for sustainable crop production in the region. Therefore, it is essential to improve WP of wheat production in this region. Within this context, deficit irrigation (DI), defined as the application of irrigation water below the full crop ET, is an important strategy to increase the efficiency of water use, particularly in dry regions (English et al., 2002; Geerts and Raes, 2009). Numerous studies have assessed the effects of DI on wheat growth, yield, and WP (Ali et al., 2007; Pradhan et al., 2014; Rao et al., 2013; Wang et al., 2012). Earlier research has shown that DI significantly improved WP by 11–40% (Rao et al., 2013; Wang et al., 2012; Zhang et al., 2006) compared to full irrigation (FI) in the wheat crop. Zhang (2003) compared the effects of DI on WP of wheat for three locations, representing different climatic conditions (Syria, North China Plain and Oregon, USA). The author concluded that the level of water application at the maximum WP differs considerably for three locations, and the optimum DI varies considerably among locations having different pedo-climatic and crop management practices. Therefore, the implementation of DI requires the quantification of crop response to water limitation under given pedo-climatic conditions of specific region (Geerts and Raes, 2009). Besides water, nutrient is another key factor determining the growth and yield of crops (Li et al., 2009). Nitrogen (N) is the key element in plant nutrition and strongly influences crop yield. The worldwide recovery of N fertilizer in wheat is low, i.e. approximately 30–50% (Spiertz, 2010). The poor recovery of applied N increases input cost to farmers and environmental problems. Therefore, improving nitrogen-use efficiency (NUE) is an important challenge to reduce input cost to farmers, and environmental impact of N losses while maintaining crop yield. It has been reported that, interaction and complementary activities of water and N are the main factors that affect yield and resource (water and N) use efficiency of crop production (Eck, 1988; Pandey et al., 2001; Pradhan et al., 2014). Eck (1988) evaluated the effects of irrigation and N application rates on WP of winter wheat, and reported that WP increased with increments of N through 140 kg ha−1 on non-stressed treatment, and through 70 kg ha−1 on stressed during head filling and grain filling stages, but applied N did not affect WP on stressed throughout crop growing season. In contrast, Pradhan et al. (2014) investigated effects of four levels of irrigation (rainfed, irrigation replenishes to 30, 60 and 100% moisture deficit from field capacity) and N (0, 30, 60 and 120 kg N ha−1 ) on WP and NUE of wheat in semi-arid region of India. They reported that the WP of wheat increased up to the application of 120 kg N ha−1 in all irrigation regimes. They observed greatest WP and NUE without any significant reduction in crop yield with application of 120 kg N ha−1 and irrigation to replenish 60% soil moisture depletion to field capacity. It is clear, therefore, the understanding of the interactive effects of water and N availability, along with the crop’s ability to efficiently use these resources (expressed by WP and NUE, respectively) are of crucial importance for improving WP and NUE while maintaining high yield of wheat in hot, arid region having sandy soils, which are vulnerable to leaching of water and soluble nutrients. The objective of this work was to study the interaction between water and N applied at different levels on growth, yield components, and yield of wheat as well as to analyze the efficiency of water and N used by the crop in an arid environment. Such a study would provide useful information to wheat production, achieving a higher grain yield and high resource use efficiency, and give insight into understanding the mechanism underlying the interaction between water and N on wheat growth and yield. Furthermore, this knowledge will aid in the development of concurrent management strategies

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for irrigation and N application amounts in wheat for the hot arid region.

2. Materials and methods 2.1. Experimental site Field experiments were conducted at the research farm of Regional Research Station, Bikaner of the Central Arid Zone Research Institute, Rajasthan, India (28◦ 4 N; 74◦ 3 E, 238.3 m altitude) during the wheat growing season (October–March) of 2011–12 and 2012–13. The climate of the site is a hot arid having 286 mm mean annual precipitation, the most of which is received during July–September. The air temperatures, precipitations and evaporations during the wheat growing seasons across the two study years measured at weather stations located 800 m away from the site are shown in Fig. 1. The soil (0–20 cm layer) of the experimental site was a sandy loam (Typic Torripssamentes, US classification) that contained 1.2 g kg −1 organic carbon (the Walkley–Black method), 4.6 mg kg −1 (Olsen) available phosphorus, 105.3 mg kg −1 (1 N NH4 acetate) available potassium, 8.4 pH (soil/H2 O, 1:2.5) and 841 g kg −1 sand (2000–50 ␮m), 46 silt g kg −1 (50–2 ␮m) and 113 g kg−1 clay (<2 ␮m).The important physicochemical properties of soil layer up to 100 cm are shown in Table 1.

2.2. Experimental design and treatments The experiment was a 6 × 4 (six irrigation levels and 4 N rates) factorial design with 24-treatment combinations. The treatments laid out in a split-plot design with irrigation in main plots (10 m wide and 37 m long, 370 m2 ), and N rates in sub-plots (10 m wide and 7 m long, 70 m2 ). The treatments comprised six levels of irrigation based on crop evapotranspiration (ETc) viz. 100% (ETm, full evapotranspiration), 90% (ETd1), 80% (ETd2), 70% (ETd3), 60% (ETd4) and 50% (ETd5) of ETc. The N rate treatments consisted four levels viz. 0, 40, 80 and 120 kg N ha−1 (designated as N0, N40, N80 and N120, respectively). The treatments were replicated three times. The experimental site was 231 m × 37 m field with a replication size of 75 m × 37 m. Sprinkler line was laid out in each main plot which offered irrigation to four sub-plots. The irrigation was applied through 32 mm PVC pipe line with a total of 24 minisprinklers (double nozzle, 2.5 mm × 1.8 mm size having discharge of 7.5 lpm at 2.5 kg cm −2 pressure; M/S Jain Irrigation Ltd; spaced at 10 m interval). A flow-meter was installed at the head of lateral pipe at each main plot to measure the applied water. Sprinkler irrigations were performed in the morning provided wind speed was <2 m s−1 . Pan evaporation and rainfall recorded from India Meteorological Department Class A Meteorological observatory located about 800 m away from the experimental site. The daily crop evapotranspiration requirement (ETc) was estimated using the equation: ETc = Epan × Kp × Kc

(1)

where Epan, pan evaporation (mm); KP , pan coefficient (0.75); KC , crop coefficient, which varies for different growth stages of the crop as per FAO 56 (Allen et al., 1998). A uniform pre-sowing irrigation of 70 mm was applied to all plots. Subsequent irrigations were applied after ≥45 mm of ETc. This resulted in irrigations every 8–10 days. The irrigation water requirement to be given through sprinkler irrigation was calculated as ETc × irrigation efficiency (80%) and a ready reckoner was prepared and irrigation was given as per irrigation treatments. N was applied through urea (46% N) in two splits, i.e., 50% at sowing and the remaining 50% with the first irrigation.

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Fig. 1. Weekly mean maximum and minimum temperatures, cumulative weekly rainfall and evaporation, and irrigation amount (full irrigation) applied in (A) 2011–12, and (B) 2012–13 during wheat growing seasons at Bikaner, Rajasthan, India. (Red line with triangles: maximum temperatures; blue line with triangles: minimum temperatures; violet unfilled bar: evaporation; green bar: irrigation; black solid bar: rainfall). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Table 1 Physico-chemical properties of the experimental soil. Soil layer (cm)

0–20 21–40 41–60 61–80 81–100

Soil texture (g kg −1 )

BD (Mg m−3 )

Sand

Silt

Clay

841 835 820 805 800

46 48 60 73 77

113 117 120 122 123

1.56 1.54 1.53 1.52 1.52

Volumetric soil water content (m3 m−3 ) FC

PWP

0.155 0.157 0.161 0.163 0.164

0.078 0.080 0.081 0.083 0.086

pH (1:2.5)

OC (g kg−1 )

8.4 8.1 8.0 8.1 7.9

1.2 1.0 0.8 0.9 0.7

BD: bulk density; FC: field capacity; PWP: permanent wilting point.

2.3. Crop management The wheat cultivar “Raj 3765” was sown on November 20 and November 25 during 2011, and 2012, respectively. The crop was sown with tractor-drawn seed drill using a seed rate of 100 kg ha−1 with row spacing of 20 cm. Seeds were treated with Thiamethoxam

30% FS (RENO) @ 3.3 ml kg −1 to control termite. Phosphorus (P2 O5 ) at the rate of 60 kg P2 O5 ha−1 was applied at the time of sowing via single super phosphate (16% P2 O5 ) to all the plots. The herbicide, 2,4 D sodium salt at 625 g ha−1 and Sulphosulfuron 75% WG + Metsulfuron 5% WG was applied at 40 g ha−1 at 35 days after

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sowing (DAS) to control weeds. The crop was harvested manually between 2 and 10 April in both years. 2.4. Sampling and measurements 2.4.1. Crop growth, yield components, and yields Leaf area and dry matter were recorded at 30, 60 and 90 days after sowing (DAS). For this purpose, plants from 0.5 m row length at two randomly selected places in the middle row of each sub-plot were selected. The plants were cut near ground level, and leaves were separated, and leaf area was recorded using a leaf area meter (Systronics India Ltd., Model 211). The whole plant (leaf + stem) was dried at 65 ◦ C and weighed to determine dry matter and converted to g m−2 . Yield components such as number of spike m−2 , number of grain m−2 , and 100-grain weight was recorded from five 1-m-row length of each sub-plot at harvest. At maturity, total above ground biomass production (ABY) and grain yield (GY) were determined on an area of 4 m2 (central 2 m × 2 m) from each sub plot by manual harvesting and was sun dried for four days and threshed separately for each experimental unit. GY was recorded and adjusted to 13% moisture content. The yield data were converted into kg ha−1 . The harvest index (HI) was calculated as the ratio of grain yield to total aboveground biomass. Protein content of grain (GPC) was determined by measuring its N concentration by Kjeldahl method and multiplying it by 6.25 to express the total protein concentration. Grain protein yield (GPY) was determined by multiplying the GPC with GY (kg ha−1 ). 2.4.2. Total water use, water productivity and yield water relationship The total water applied is the sum total of irrigation water and rainfall. For determining the soil water consumed by the crop (ET), soil profile water content (SWC) was measured at the time of sowing and harvest in 0–150 cm soil by thermo-gravimetric method. For SWC determination, soil samples were collected from 0 to 15, 15–30, 30–60, 60–90, 90–120, and 120–150 cm depths. The samples were then oven dried (105 ◦ C) and moisture content was calculated on dry weight basis. The percent soil moisture on dry weight basis was converted to depth wise by multiplying the moisture content with bulk density and thickness of the respective soil layer. The crop evapotranspiration (ET) was calculated by using the soil water balance equation: ET = P + I + Cp − S − D − R

(2)

Where P is precipitation, I is irrigation, Cp is contribution through the capillary rise from ground water, S is the change in soil moisture between sowing and harvesting, D is deep drainage and R is run off. The Cp was assumed negligible, this is because the level of the water table near the experimental field was >30 m. R was assumed to be zero as the soil at the experimental site was sandy, had a good infiltration rate and each sub-plot was protected by a 35 cm bund. The D was assumed to be negligible since the water storage capacity of soil at the experimental site was high and normally exceeded the rainfall volume required to saturate that capacity or storage and the change in SWC below 100 cm were negligible. Rathore et al., (2014a,2014b) under similar soil and climatic conditions and irrigation amount also pointed out that D and R were negligible when sprinkler irrigation amount was controlled. Thus, Eq. (2) reduces to the following form for calculating ET: ET = P + I − S

(3)

Physical WP in terms of ET was determined using the following equation: WP GYET = GY/ET

(4)

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where WP GYET is water productivity (kg m−3 ) in terms of grain yield per unit of ET, GY is grain yield (kg ha−1 ), and ET is evapotranspiration (m3 ha−1 ). To determine the water use yield relationship, dimensionless parameters in relative yield reduction and relative reduction in ET were used: 1–Y ai /Y m = Kyi (1-ETai /ETm )

(5) (kg ha−1 )

ith

where Yai is the actual yield corresponding to irrigation and 120 kg ha−1 N level, Ym is the maximum yield (kg ha−1 ) across all irrigation and nitrogen level, ETai is actual ET (mm) corresponding to ith irrigation and 120 kg ha−1 N level, ETm is maximum ET (mm), Ya /Ym is relative yield, ETa /ETm is relative ET, and Kyi is a yield response factor at ith irrigation level defined as decrease in yield with respect to per unit decrease in ET (Doorenbos and Kassam, 1979).The combined Ky factor was also calculated by plotting (1-ETai /ETm ) versus (1-Yai /Ym ),and fitting the regression line passing through origin in which slope of the equation represents the combined Ky factor. 2.4.3. Nitrogen uptake and nitrogen use efficiencies Plant samples (both grain and straw) were taken at harvest stage each year. Samples were oven-dried, ground and analyzed for N contents using the Kjeldahl method. The N content of the seed and straw were multiplied with their respective yields in order to calculate the N uptake by the seed and straw. The N uptake by the seed and straw were added together to determine the total N uptake (TNU) and converted to kg N uptake ha−1 . The N use efficiency (NUE) measures, i.e., agronomic efficiency (AEN ), recovery efficiency (REN ) and physiological efficiency (PEN ) were calculated as described by Mon et al. (2016): AEN (kggrainkgNapplied−1 ) : (Y i − Y c )/Nfi

(6)

REN (%) = (Nui − Nuc )/Nfi × 100

(7)

PEN (kggrainkgNuptake−1 ) = (Y i − Y c) /(Nfi − Nfc )

(8)

where Yi , and Yc is seed yield (kg ha−1 ) in N-fertilized plot, and zero-N fertilized plot, respectively. Nfi and N fc are applied N as fertilizer in different treatments and control, respectively (kg ha−1 ); and N ui and Nuc are the TNU in different N treatments and control, respectively (kg ha −1 ). 2.5. Statistical analyses The data recorded for different parameters were analysed with the help of analysis of variance (ANOVA) technique (Gomez and Gomez, 1984) for split-plot design using SAS 9.1 software (SAS Institute, Cary, NC). Data from each year were analyzed separately. The significance of the treatment effect was determined using the Ftest, and comparisons of means were carried out using the least significant difference (LSD) at the 5% level of significance. Regression analysis was performed between water applied and ET, and ET and yield. 3. Results and discussion 3.1. Weather conditions The air temperatures, precipitation, evaporation and irrigation amount (used for FI treatment) applied during the wheat growing season across the two study years measured at a weather station close (∼800 m) to the experimental site are shown in Fig. 1. The wheat-growing period, November to March, was characterized by dry winters. The daily minimum and maximum temperatures within the crop season varied between −0.3 to 23.5 ◦ C,

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and 15.6–42 ◦ C, respectively. The daily evaporation (measured by USWB Class A Pan evaporation) ranged between 1–10.7 mm. 3.2. Plant growth The irrigation (I), nitrogen (N) and their interaction (I × N) had significant (P < 0.01) effects on leaf area and dry matter measured at 60 and 90 DAS in both years (Table 2). The leaf area and dry matter measured at 60 and 90 DAS increased with an increase in irrigation level and N rates. Compared to full irrigation (ETm), irrigation at ≤ETd3 caused 11–36% and 14–41% (mean of two years) reduction in leaf area and dry matter production measured at 90 DAS, respectively. The leaf area and dry matter increased with an increase in N rates in both years. Averaged across years and irrigation level, the N120 fertilized plots had 1.6–1.7-times greater leaf area and dry matter measured at 90 DAS, respectively, compared to N0 fertilized plots. Water and N-deficit cause a marked reduction in cell division, cell-elongation and duration of cell elongation (Farooq et al., 2009; Novoa and Loomis, 1981) which results in the lower leaf area. The reduction in dry matter under declined water and N supply (Table 2) might be attributed to reduced canopy absorption of PAR due to water and N-deficit induced limitation of leaf area (Ram et al., 2013). In this study dry matter is positively related to leaf area (r2 = 0.94, P = 0.01). The growth response to N rates modified with irrigation levels (Table 2). The highest leaf area and dry matter were observed under the conjunct influences of higher irrigation (ETm, ETd1) and N120 in this study implying that adequate water and N supply are essential to achieve greater leaf area and dry matter in hot, arid environment. The growth response to added N reduced with a reduction in water supply in this study (Table 2). It has been reported that the effectiveness of N-fertilizer is reduced due to reduction in mineralization and transport of N to the roots under decreased soil water availability (Gonzalez-Dugo et al., 2010). 3.3. Yield components I, N and their interaction effects were detected to be significant for yield components in both years (Table 3). Spike number, grain number, and 100–grain weight ranged from 140 to 303 m−2 , 4159 to 15,191 m−2 and 2.67 to 4.40 g, respectively.The yield components declined with a decrease in irrigation and N rates. The water and N-deficit induced decline was greater in grain number and spike number compared to that in grain weight. The ≥ETd1 had a significantly greater yield component compared to ≤ETd3 irrigation levels in both years. Averaged across years and N rates, irrigation at ≤ ETd3 caused 18–40, 11–29, and 15–25% reduction in grain number, spike number, and grain weight, respectively. Yield component increased with an increase in N rates. Averaged across years and irrigation levels, N120 fertilized plots had 1.2, 1.6 and 2.1–folds greater grain weight, spike number, and grain number respectively, compared to zero N-fertilized plots. Adequate production and transport of photoassimalates maintained by leaf area and dry matter are essential for full development of yield component in wheat (Sattore and Slafer, 1999). The significant reduction in GN (grain number) and GW (grain weight) under decreased supply of water and N observed in this study might be attributed to decreased availability of photosynthates [evident by the less leaf area and dry matter under lower water and N supply condition (Table 2)], and reduced transport of assimilates to grain. The effects of N rates on yield components varied with irrigation levels. The higher N rates were ineffective to increase yield component with decreased water supply in this study. The N120 at ≥ETd1 recorded highest yield component. The spike number and grain number increased up to N80 at ≥ETd2 irrigation levels, while spike number and grain number increased up to N40 at ETd3 irrigation level. At ETd5, the spike num-

ber was not affected by N rates in either year. A significant increase in grain weight was recorded up to N80 at ≥ETd3, and up to N40 at ≤ETd4 irrigation levels. An adequate supply of photosynthates due to the greater leaf area and dry matter under well-watered conditions (ETm and ETd1) might be an explanation for greater yield components at higher irrigation (ETm and ETd1) and N rates in the present study. 3.4. Yield and HI I, N and their interaction (I × N) had significant effects on yields [grain yield (GY) and above ground biomass yield (ABY)] and harvest index (HI) (Table 4). Previous studies have shown that compared to full irrigation, the moderate deficit irrigation could give similar (Zhang, 2003), higher (Zhang et al., 2006), or lower (Wang et al., 2012) wheat yield. An application of 90% of the full irrigation (ETd1) produced a slightly greater yield than full irrigation, while application of 80% of the full irrigation (ETd2) caused 4–6% reduction in yield compared to full irrigation (ETm) in this study (Table 4). It has been reported that moderate deficit irrigation could enhance root growth, facilitate the remobilization of reserve C to the grains, accelerate grain filling (Zhang et al., 1998; Bandyopadhyay et al., 2010) and higher HI (Table 4), which might be responsible for better grain yield with moderate deficit irrigation (ETd1 and ETd2) observed in the present study. The irrigation application less than 20% of crop ETm caused 20–50% reduction in grain yield, and 18–46% reduction in biomass yield (Table 2). Rao et al. (2013) demonstrated that applying 25–54% less water than full irrigation (ET100%) caused a reduction of 12–47% in grain yield and 10–43% of biomass yield of wheat in arid regions of India. A marked reduction in grain yield under severe deficit irrigation levels might be attributed to water-deficit induced reduction in yield component (Table 3), and this is confirmed by our correlation results that grain yield is strongly related to grain number (r2 = 0.96, P = 0.01)), spike number (r2 0.94, P = 0.01)) and grain weight (r 2 = 0.89, P = 0.01). The marked reduction in leaf area and the number of tillers (Table 2) is a possible explanation for reduced ABY under severe deficit irrigation levels observed in this study. The moderate deficit irrigation levels had greater HI than full irrigation (Table 4). Palta et al. (1994) reported that mild water stress in wheat may lead to a better translocation of the carbon reserve from the leaf and sheath to grain which leads to improvement of HI. N fertilization played an important role in yield promotion (Table 4). Averaged across years and irrigation levels, N120 fertilized plots produced 2-folds greater ABY, and 2.3-folds greater GY than N0 fertilized plots. Rathore et al. (2016) also reported an increase in grain yield of wheat (1.3–2.4-times) with an increase in N rates under hot arid environment. An adequate supply of N increases canopy green area, number of tillers, yield component (especially grain and spike number) which is closely related to biomass and grain yields in wheat (Shearman et al., 2005). In contrast to yields, the N application increased HI up to N80, and thereafter the HI was not improved with a rise in N rates in this study. The results implied that N application up to N80 improved both yield and biomass partitioning to sink, while at higher N rates the grain yield followed biomass yield without significant effect on partitioning. The results are in agreement with the findings of Sattore and Slafer (1999), who demonstrated that HI is generally found to decrease with N supply at higher N rates, as grain yield declined before above ground dry matter production. The yield response to N rates modified with irrigation levels (Table 4). The yield response to higher N rates declined with a decrease in irrigation levels. The highest yields were observed under the conjunct influences of higher irrigation (ETm, ETd1) and N (N120) rate during both years. The N0 fertilized plots produced lowest yields at all irrigation levels in either year. A significant

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Table 2 Leaf area and dry matter production of wheat under various irrigation and nitrogen treatments in 2011–12, and 2012–13, at Bikaner, Rajasthan, India. Year

Irrigation level

N rate (kg ha−1 )

Leaf area (cm−2 plant−1 ) **

2011–12

30 DAS

60 DAS

90DAS

30 DAS

60 DAS

90DAS

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

36 a*** 86 a 127 a 133 a 42 a 88 a 123 a 133 a 40 a 88 a 128 a 137 a 47 a 95 a 130 a 133 a 44 a 99 a 135a 126 a 43 a 99 a 109 a 101 a

70 h 140 e–g 240 bc 295 a 72 h 149 ef 248 b 309a 75 h 142 e-g 236 bc 291a 69 h 139 fg 220c 219 c 63 h 134 fg 175 d 163 de 53 h 121 g 151 d–f 141 e–g

78 g b 162 e 268 b 338 a 82 g 169 ef 273 b 349 a 80 g 164 ef 264 bc 333 a 82 g 163 ef 240 c 253 bc 73 g 156 ef 202 d 200 d 68 g 143 f 179 de 171 e

62 a 79 a 90 a 95 a 58 a 81 a 88 a 94 a 68 a 75 a 95 a 101 a 70 a 83 a 90 a 90 a 68 a 79 a 87 a 83 a 61 a 73 a 84 a 81 a

247 g–i 370 d 452 ab 475 a 239 hi 388 c 471 a 488 a 265 f-h 374 cd 450 bc 463 a 289 fg 371 cd 406 bc 410 bc 239 hi 303 de 335 de 301 ef 230 i 275 f–h 290 fg 278 f–h

502 kl 803 ef 1087 bc 1192 a 519 i–k 799 ef 1069 c 1166 ab 517 ijk 774 ef 1032 c 1080 bc 497 kl 730 eg 922 d 939 d 474 kl 662 gh 695 fg 691 fg 414 l 603 hi 576 hij 513 jk

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

33 a 77a 119a 125 a 37 a 79 a 115 a 125 a 38 a 79 a 120 a 132 a 46 a 97 a 139 a 133 a 43 a 116 a 130 a 123 a 40 a 105 a 126 a 117 a

58 f 127 e 226 bc 278 a 65 f 134 e 234 b 289 a 58 f 127 e 219 bc 284 a 58 f 138 e 206 c 228 bc 54 f 139 e 174 d 174 d 51 f 119 e 147 e 138 e

73 i 152 gh 284 c 373 a 79 i 162 fg 287 c 381 a 75 i 154 gh 286 c 373 a 73 i 153 g 256 d 314 b 67 i 146 gh 210 e 218 e 63 i 132 h 182 f 181 f

60 a 72 a 86 a 92 a 62 a 76 a 85 a 90 a 65 a 75 a 87 a 89 a 68 a 78 a 86 a 82 a 66 a 75 a 81 a 78 a 65 a 72 a 81 a 78 a

240 hi 362 de 446 ab 466 a 249 hi 377 cd 458 ab 480 a 261 g-i 366 de 442 bc 450 ab 280 f-h 362 de 413 b-d 401 cd 248 hi 298 fg 329 ef 299 fg 227 i 271 g-i 272 g-i 278 f-h

480 jk 796 f 1116 c 1232 a 498 jk 791 f 1098 c 1206 ab 496 j 767 f 1061 cd 1120 bc 476 jk 723 g 951 e 979 cd 453 jk 655 gh 724 fg 731 fg 392 k 596 i 597 i 541 h-j

Irrigation level (I) N rate (N) I×N

NS**** 8 NS

19 12 28

21 11 28

NS 5 NS

30 18 44

65 37 90

Irrigation level (I) N rate (N) I×N

NS 7 NS

28 11 27

18 10 25

NS 6 NS

29 17 41

67 38 94

ETm*

ETd1

ETd2

ETd3

ETd4

ETd5

2012–13

Dry matter (g m−2 )

ETm

ETd1

ETd2

ETd3

ETd4

ETd5

LSD 5% 2011–12

2012–13

* ** *** ****

ETm, ETd1,ETd2,ETd3,ETd4 and ETd5 represent irrigation at 100, 90, 80, 70, 60 and 50% ETc, respectively. DAS stand for days after sowing. Within a column for each year, means followed by the same letter/s are not significantly different at the = 0.05 level by LSD test. NS means non-significant at the P = 0.05 level.

increase in yields was recorded up to N 80 at ETd2 and ETd3 irrigation levels, while at ≤ ETd4, the significant increase in yields was recorded up to N40. At ETd5, the N120 fertilized plots had lower yields than N80 fertilized plots. Our results that optimum N supply under non-water limiting conditions can result in greater yields, but under water-limiting conditions, may increase the severity of water-deficit induced reduction in yield are in agreement with the findings reported by Frederick and Camberato (1995).

3.5. Quality The grain protein content (GPC) was significantly different (P < 0.01) between irrigation levels and N rates for both years (Table 4). The GPC increased with a decrease in irrigation rate and an increase in N rates. Averaged across years and N rates, the ETd4 had greatest GPC (10.7%) followed by ETd5 (10.7%), ETd3 (10.6%), ETd2 (10.5%) and ETd1 (10.4%). Our observation that GPC of wheat

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Table 3 Yield components of wheat under various irrigation and nitrogen treatments in 2011–12, and 2012–13, at Bikaner, Rajasthan, India. Year

Irrigation level

N rate (kg ha−1 )

Spike number (m−2 )

Grain number (m−2 )

100–grain weight (g)

2011–12

ETm*

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

149 g** 224 cd 269 a 277 a 159 fg 218 c-e 271 a 281 a 160 fg 209 cde 260 ab 264 ab 163 fg 192 ef 225 bc 236 abc 161 fg 185 efg 179 efg 182 efg 155 fg 181 e-g 165 fg 156 fg

4796 k 8307 ef 11278 abc 12815 a 5153 jk 8295 ef 11446 a-c 12678 ab 5292 i-k 7887 e-g 10441 cd 11195 bc 5408 i-k 7194 e-k 8757 e 9028 de 4997 k 6547 g-j 6675 g-j 6804 f-i 4749 k 6422 h-k 6111 h-k 5674 h-k

3.43 d-f 3.55 c-e 3.79 b-d 4.18 a 3.44 d-g 3.58 c-e 3.82 ab 4.12 ab 3.32 e −g 3.54 c-e 3.74 cd 3.76 bd 3.07 gh 3.45 d-f 3.58 c-e 3.53 c-e 3.03 gh 3.33 d-f 3.43 c-e 3.35 c-e 2.87 h 3.10 gh 3.13 f-h 3.10 gh

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

146 j 225 df 281 ab 300 a 156 h-j 222 d-f 285 ab 303 a 163 h-j 213 d-g 272 a-c 287 ab 164 h-j 193 f-h 237 c-e 252 b-d 146 ij 175 h-j 194 f-h 202 e-g 140 j 171 h-j 180 hi 176 hj

4507 jk 8145 fg 12818 bc 15053 a 4925 jk 8671 ef 13076 bc 15191 a 5337 i-k 8258 fg 11738 cd 13387 b 5389 i-k 7570 fg 9859 e 10201 de 4527 jk 5841 h-j 7624 fg 8108 fg 4159 k 5779 ij 7016 gh 6691 g-i

3.33 d-f 3.45 c-e 4.18 a 4.40 a 3.34 d-f 3.48 c-e 4.21 a 4.37 a 3.22 eg 3.44 c-e 4.13 ab 4.10 ab 2.99 f-h 3.25 c-e 3.77 bc 3.76 bc 2.83 h 3.13 d-g 3.62 cd 3.60 cd 2.67 g-i 2.90 g-i 3.22 e-g 3.30 d-f

Irrigation level (I) N rate (N) I×N

26 16 39

999 623 1526

0.23 0.14 0.35

Irrigation level (I) N rate (N) I×N

27 16 40

1021 635 1557

0.22 0.15 0.36

ETd1

ETd2

ETd3

ETd4

ETd5

2012–13

ETm

ETd1

ETd2

ETd3

ETd4

ETd5

LSD 5% 2011–12

2012–13

*

ETm, ETd1,ETd2,ETd3,ETd4 and ETd5 represent irrigation at 100, 90, 80, 70, 60 and 50% ETc, respectively. Within a column for each year, means followed by the same letter/s are not significantly different at the = 0.05 level by LSD test.

**

decreases with an increase in irrigation amount is consistent with the results reported by Coventry et al. (2011), and Ram et al. (2013). Brooks et al. (1982) demonstrated that the water deficit hinders the starch synthesis more than that of protein formation. The GPC increased with an increase in N rates. The I, N and their interaction had significant effects on grain protein yield (GPY) in both years. The GPY ranged from 127 to 557 kg ha−1 . Averaged across years and N rates, the ETm produced 1.2, 1.6 and 2.0-folds greater GPY compared to ETd3, ETd4 and ETd5 irrigation levels, respectively. The GPY increased with a rise in N rates up to N120 in both years. Averaged across years and irriga-

tion levels, the N40, N80 and N120- fertilized plot produced 1.6, 2.3 and 2.5-times greater GPY compared to N0 fertilized plots. The GPY response to N rates varied with irrigation levels. The N120 fertilized plots at ETd1 and ETd2 recorded maximum GPY. The GPY increased up to N120 at ≥ ETd1, while at ETd2 and ETd3 irrigation levels a significant increase in GPY was recorded up to N80. At ETd5 irrigation level, a significant increase in GPY was recorded only up to N40. In contrast to GPC, GPY was greater with higher irrigation and N rates. In-fact, the GPY is product of yield and protein contents of grain, and greater grain yield under higher water and N

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239

Table 4 Yields, harvest index, grain protein content and grain protein yield of wheat under various irrigation and nitrogen treatments in 2011–12, and 2012–13,at Bikaner, Rajasthan, India. Year

Irrigation level

N rate (kg ha−1 )

Grain yield (kg ha−1 )

Aboveground biomass yield (kg ha −1 )

Harvest index

Grain protein content (%)

Grain protein yield (kg ha−1 )

2011–12

ETm*

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

1622 i-k** 2912 de 4182 bc 4704 a 1777 ij 2928 d 4270 bc 4561 a 1775 ij 2856 e 3927 c 4069 c 1634 i-k 2517 ef 3260 d 3308 d 1501 jk 2222 h 2332 fg 2275 f-h 1304 k 1997 g-i 1868 h-j 1608 i-k

4210 ij 7140 e 9732 bc 10678 a 4426 hi 7060 e 9636 bc 10174 ab 4365 hi 6813 e 9259 c 9611 bc 4276 ij 6415 ef 8089 d 8213 d 3976 ij 5689 fg 5829 fg 5640 fg 3429 j 5164 gh 4688 hi 3904 ij

0.38 e 0.41 cd 0.43 ab 0.44 ab 0.40 c-e 0.41 cd 0.44 ab 0.45 a 0.41 cd 0.42 bc 0.42 bc 0.42 bc 0.38 cd 0.39 de 0.40 de 0.40 de 0.38 e 0.39 de 0.40 de 0.40 de 0.38 e 0.39 de 0.40 c-e 0.41 cd

10.08 a 10.25 a 10.31 a 10.56 a 10.08 a 10.17 a 10.25 a 10.58 a 10.10 a 10.25 a 10.33 a 10.73 a 10.17 a 10.25 a 10.38 a 10.79 a 10.23 a 10.38 a 10.52 a 10.90 a 10.08 a 10.35 a 10.65 a 10.90 a

163 ij 298 de 431 b 497 a 180 hi 297 e 438 b 482 a 179 hi 293 e 406 bc 436 b 165 ij 258 ef 338 cd 357 d 154 ij 229 fg 246 fg 248 fg 131 j 207 gh 199 h 175 hi

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

1510 ij 2768 e 4466 c 5136 a 1649 ij 2783 e 4558 bc 5004 ab 1647 ij 2716 e 4331 c 4604 bc 1521 ij 2401 e-g 3548 d 3652 d 1401 j 2127 f-h 2490 e-g 2525 ef 1223 k 1918 hi 2037 gh 1811 hi

4068 h 7146 de 10215 bc 11597 a 4397 gh 7107 de 10192 bc 10698 ab 4333 gh 6802 e 9426 c 9942 bc 4286 gh 6334 ef 8143 d 8248 d 4173 gh 5927 e 6409 ef 6263 ef 3666 h 5275 fg 5292 f 4698 gh

0.37 ef 0.39 cd 0.44 b 0.44 b 0.38 c-e 0.39 cd 0.45 ab 0.47 a 0.38 c-e 0.40 c 0.46 ab 0.46 ab 0.35 c-h 0.38 c-e 0.44 b 0.44 b 0.34 f-h 0.36 e-g 0.39 cd 0.40 c 0.34 h 0.36 e-g 0.39 cd 0.40 cd

10.42 a 10.58 a 10.60 a 10.85 a 10.38 a 10.50 a 10.54 a 10.92 a 10.46 a 10.58 a 10.69 a 11.00 a 10.52 a 10.54 a 10.71 a 11.13 a 10.56 a 10.69 a 10.85 a 11.23 a 10.40 a 10.65 a 10.98 a 11.21 a

157 i 293 e 473 c 557 a 171 hi 292 e 480 c 546 ab 172 hi 288 e 463 c 506 bc 160 hi 253 ef 380 d 406 d 148 i 227 fg 271 e 283 e 127 i 204 gh 224 fg 203 gh

Irrigation level (I) N rate (N) I×N

293 175 428

654 359 879

0.01 0.01 0.02

0.26 0.15 NS***

27 17 42

Irrigation level (I) N rate (N) I×N

328 185 453

702 470 1151

0.01 0.01 0.02

0.27 0.14 NS

32 19 46

ETd1

ETd2

ETd3

ETd4

ETd5

2012–13

ETm

ETd1

ETd2

ETd3

ETd4

ETd5

LSD 5% 2011–12

2012–13

* ** ***

ETm, ETd1,ETd2,ETd3,ETd4 and ETd5 represent irrigation at 100, 90, 80, 70, 60 and 50% ETc, respectively. Within a column for each year, means followed by the same letter/s are not significantly different at the = 0.05 level by LSD test. NS means non-significant at the P = 0.05 level.

rates might be responsible for their greater GPY compared to that of lower irrigation and N rate treatments observed in this study.

3.6. Water consumption The effects of irrigation, N rates, and I × N interaction were significant on water consumption (ET) (Table 5). The water con-

sumption declined with a decrease in irrigation and N rates. Averaged across years and N rates, compared to ETm, the ETd3, ETd4 and ETd5 recorded 26, 37, and 41% reduction, respectively in ET. The ET increased with an increase in N rates. Averaged across years and irrigation levels, N120 fertilized plots had 8% greater ET than N0 fertilized plots. The reduced availability of soil-water along with water-deficit induced reduction in leaf area (Table 2) and sto-

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Table 5 Water use and water productivities of wheat under various irrigation and nitrogen treatments in 2011–12, and 2012–13 at Bikaner, Rajasthan, India. Year

Irrigation level

N rate (kg ha−1 )

Irrigation (mm)

Water consumption* (mm)

WPGYET (kg m−3 )

2011–12

ETm**

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

460 460 460 460 421 421 421 421 382 382 382 382 343 343 343 343 304 304 304 304 265 265 265 265

319.0 bc*** 325.7 b 329.7 ab 341.3 a 297.3 d 304.0 d 310.0 cd 314.7 bc 266.3 fg 276.3 ef 284.7 e 289.7 de 233.0 i 240.7 i 246.7 hi 254.0 gh 188.0 kl 195.0 k 205.3 j 210.0 j 179.3 l 186.0 kl 195.0 k 198.7 jk

0.51 i 0.89 ef 1.27 b 1.38 ab 0.60 hi 0.96 de 1.38 ab 1.45 a 0.66 h 1.03 cd 1.38 ab 1.40 ab 0.70 h 1.04 cd 1.32 ab 1.30 b 0.80 fg 1.13 c 1.13 c 1.08 cd 0.72 gh 1.07 cd 0.96 de 0.81 fg

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

440 440 440 440 403 403 403 403 366 366 366 366 329 329 329 329 292 292 292 292 255 255 255 255

304.2 cd 309.6 bc 322.0 ab 325.7 a 287.9 ef 293.9 c-e 318.9 ab 301.0 ab 266.8 g 271.2 g 274.2 fg 275.7 ef 225.7 i 233.3 hi 236.7 hi 238.0 hi 196.1 jk 199.5 jk 206.8 jk 210.2 j 181.7 lm 187.9 k-m 193.3 k-m 194.6 k-m

0.50 g 0.90 e 1.39 bc 1.58 ab 0.57 fg 0.95 e 1.43 bc 1.57 ab 0.62 fg 1.00 e 1.58 ab 1.67 a 0.67 fg 1.03 de 1.50 ab 1.54 ab 0.71 f 1.06 de 1.21 cd 1.20 d 0.68 fg 1.02 de 1.05 de 0.93 e

Irrigation level (I) N rate (N) I×N

10.9 7.0 16.8

0.08 0.05 0.12

Irrigation level (I) N rate (N) I×N

9.2 6.1 15.2

0.16 0.08 0.19

ETd1

ETd2

ETd3

ETd4

ETd5

2012–13

ETm

ETd1

ETd2

ETd3

ETd4

ETd5

LSD 5% 2011–12

2012–13

* ** ***

Water consumption is water used by the crop (ET) which is calculated by using Eq. (3). ETm, ETd1,ETd2,ETd3,ETd4 and ETd5 represent irrigation at 100, 90, 80, 70, 60 and 50% ETc, respectively. Within a column for each year, means followed by the same letter/s are not significantly different at the = 0.05 level by LSD test.

matal conductance (Davies and Zhang, 1991) are responsible for less ET under deficit irrigation levels. An increase in ET by crop with N application might be attributed to the increased leaf area and biomass (Table 2) with application of N (Zhang et al., 1999; Qi et al., 2009). The effects of N rates on ET varied with irrigation levels. The ET ranged from 266.3 to 341.3 in 2011–12 and 266.8–325.7 mm in 2012–13 among N rates at ≥ ETd2 irrigation levels, while at ≤ETd3 irrigation levels the ET ranged from 179.3 to 250.4 mm in 2011–12

and 181.7–238.0 mm in 2012–13. Frederick and Camberato (1995) demonstrated that N fertilization increases root growth and leads to greater absorption of soil water during the crop season in wheat. The relationship between ET and irrigation amount applied were linear and had a high coefficient of determination (R2 = 0.98) (Fig. 2), which is expected, because the precipitation during the crop growing season (November to March) was negligible during both years (Fig. 1), and ET was mainly from applied irrigation water.

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Fig. 2. The relationship between irrigation water applied and crop water consumption (ET) in wheat in 2011–12, and 2012–13 during wheat growing seasons at Bikaner, Rajasthan, India. (Each point represents an average value of 12 samples).

3.7. Water productivity There have been different and contradictory results for wheat, when WPs under full and deficit irrigations are compared. Studies have shown that compared to full irrigation, the deficit irrigation could give a greater (Pradhan et al., 2014), or lower (Johnson et al., 1984) WPs in wheat. In the present study, moderate deficit irrigation (ETd1 and ETd2) recorded greater WPs compared to full (ETm) and severe deficit irrigation (ETd4 and ETd5) levels (Table 5). The improved WPs at a moderate water deficit could be explained by several reasons. First, the moderate deficit irrigation caused less reduction in grain yield [4 and 19% reduction in grain yield at ETd2 and ETd3 compared to full irrigation (Table 4)] compared to the reduction in ET [14 and 26% reduction in ET at ETd2 and ETd3 compared to full irrigation (Table 5)]. Second, the moderate deficit irrigation increased HI (Table 4), and HI are closely associated with a higher WPs in cereals (Wang et al., 2016). Third, previous studies have shown that more efficient use of available soil water in the root zone (Zhang et al., 2006), leads to greater WPs at moderate deficit irrigation than full irrigated conditions. WPs increased with rising N rates, although the differences in WP between N100 and N120 rates were not significant (Table 5). Averaged across years and irrigation levels, application of N120 recorded 2.0- times greater WPGYET than N0. The improved WP with N fertilization observed in this study might be attributed to increased leaf area (Table 2) which leads to a reduction in E (evaporation) component of ET (Frederick and Camberato, 1995); and smaller increase in ET (Table 5) compared to yield (Table 4) (Hatfield et al., 2001). The N120 at ETd2 irrigation levels had greatest WP in both years. A significant increase in WP was recorded up to N 80 at ≥ ETd3 irrigation levels, while a significant increase in WP was recorded up to N40 at ≤ ETd4 irrigation levels. The results are in agreement with the findings of Amir et al. (1991), and Wang et al. (2012), who demonstrated that the addition of N in N-deficient soil increases WP, when water is available. The results implying that adjusting N rates according to availability of water are essential to achieve greater WP in wheat.

Fig. 3. The relationship between wheat grain yield (y) and crop water consumed (ET) during 2011–12, and 2012–13 in wheat at Bikaner, Rajasthan, India. (Each point represents an average value of 12 samples).

grain yield to ET (Fig. 3) suggests that a policy for maximizing grain yield under limited water resources conditions should be avoided, and maximizing WP is recommended for sustainable use of water resources in this region. In water scarce areas such as arid region, high WP for an irrigation scheduling should be associated with high or acceptable yield (Ali et al., 2007). For this, we used the two curves of grain yield and WP with ET to determine the optimum ET amount (Fig. 4).The intersection points of two curves showed that optimum ET was about 280–300 mm corresponding to the irrigation amount of about 400 mm with about 3000–3200 kg ha−1 GY and 1.18–1.20 kg m−3 WPGYET . With this optimal irrigation amount, 95% of the maximum GY and WP can be achieved. The relationship between grain yield and water consumption (ET) under different N rates exhibited a significant non-linear relationship (R2 = 0.96–0.98) (Fig. 5). The yield increased with an increase in ET, but the magnitude of response to water differed for individual N rate. The significant non-linear relationship between grain yields to the total ET corresponding to different N rates observed in this study indicates that yield response to ET depends on N rates, and adjusting N rates in accordance with water availability is essential to produce better yield. These empirical relationships may be used to estimate the levels of irrigation water (as ET is strongly related to the amount of irrigation water applied depicted in Fig. 2) and N for achieving higher yield. The good linear relationship (R2 = 0.87 to 0.91) between the relative GY decrease and ET deficit were observed in both years (Fig. 6). The yield response index (Kyi ) for ETd1, ETd2, ETd3, ETd4 and ETd5 were 0.34, 0.67, 1.07, 1.43 and 1.61, respectively in 2011–12; the Kyi were 0.39, 0.81, 1.16, 1.45 and 1.64 for the respective irrigation levels in 2012–13.The combined yield response factor (Ky ) had a value between 1.3–1.4. 3.9. Nitrogen uptake and use efficiency

3.8. Water-yield relations The grain yield exhibited a significant polynomial relationship with the amount of water consumption by crop (ET) applied in both years (R2 = 0.98–0.99) (Fig. 3). The non-linear relationship of

The I, N and I × N interaction effects had significant effects on the total nitrogen uptake (TNU) in both years (Table 6). The TNU increased with an increase in irrigation and N rates. A marked reduction in TNU was recorded with ≤ETd3 irrigation levels. Aver-

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Fig. 6. The relationship between relative yield reduction and relative evapotranspiration deficit for wheat during 2011–12, and 2012–13 at Bikaner, Rajasthan, India.

Fig. 4. Crop water consumed (ET), yield and water productivity relationship in wheat during (A) 2011–12, and (B) 2012-13 in wheat at Bikaner, Rajasthan, India. (Each point represents an average value of 12 samples).

aged across years and N rates, compared to ETm, the TNU declined by 17, 33 and 45% at ETd3, ETd4 and ETd5 irrigation levels, respectively. The crop N uptake depends on both soil N supply (N supply approach) and crop growth (N demand approach); and soil water content affects both the availability of N and crop growth (Gonzalez-Dugo et al., 2010). A reduction in N uptake under deficit irrigation compared to full irrigation observed in this study might be attributed to reduction in N demand due to water-deficit induced reduction in crop growth (Table 2), along with reduction in mineralization (Lemaire et al., 2004), and transport of N to soilroot interface (Gonzalez-Dugo et al., 2010). The TNU increased with a rise in N rates, and the application of N40, N80 and N120 had 60–62, 104–125 and 117–144% greater TNU respectively, compared to N0. The increase in TNU with an increase in N rates is due to

Fig. 5. Wheat yield response to crop water consumed (ET) under different N rates during (A) 2011–12, and (B) 2012–13 in wheat at Bikaner, Rajasthan, India. The N0, N40, N80 and N120 represent application of 0, 40, 80, and 120 kg N ha−1 , respectively. (Each point represents an average value of 3 samples).

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Table 6 Nitrogen uptake and nitrogen −use efficiencies of wheat under various irrigation and nitrogen treatments in 2011–12, and 2012–13, at Bikaner, Rajasthan, India. PEN (kg grain kg N uptake −1 )

Year

Irrigation level

N rate (kg ha−1 )

Total N uptake (kg ha−1 )

AEN (kg grain kg N−1 )

REN (%)

2011–12

ETm*

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

39 i-k** 68 e 97 c 110 a 42 ij 68 e 97 c 108 ab 42 ij 67 ef 93 c 100 bc 39 i-k 61 f 79 de 84 d 37 jk 54 fg 58 fg 58 fg 32 k 50 gh 47 hi 41 ij

– 32.3a 32.0a 25.7abc – 28.8 ab 31.2 a 23.2 a-c – 27.0 ab 26.9 ab 19.1 c-e – 22.1 b-d 20.3 cd 13.9 d-f – 18.0 de 10.4 d-g 6.5 fg – 17.4 c-e 7.0 fg 2.5 g

– 75.1 a 73 2 ab 59.1 a-d – 66.3 a-c 70 ab 55 b-d – 64.5 a-c 64.2 a-c 48.3 c-e – 53.1 b-e 49.2 c-e 37.4ef – 44.2 ef 26.5 fg 18.4 gh – 44.4 ef 19.4 gh 08.1h

N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120 N0 N40 N80 N120

37 h 67 e 104 c 121 a 40 f-h 68 e 105 c 118 ab 40 f-h 66 e 100 c 109 ab 39 f-h 59 e 83 c 89 b 37 h 55 ef 63 d 65 d 33 h 50 fg 53 f 49 fg

– 31.5 a-c 37.0 a 30.2 bc – 28.4 cd 36.4 ab 28.0 cd – 26.7 cd 33.5 ab 24.6 c-e – 22.0 d-f 25.3 cd 17.8 fg 18.1 e-g 13.6 gh 9.4 hi – 17.4 fg 10.2 hi 4.9 i

– 76.2 ab 83.2 a 70.4 a-c – 68.1 a-c 80.3 ab 65.2b-d – 65.1 b-d 74.3 ab 57.2 c-e – 52.2 de 56.3 de 42.4 ef – 45.4 d-f 33.2 fg 24.2 gh – 43.2 ef 25.3 f-h 13.2 h

Irrigation level (I) N rate (N) I×N

6 3 8

7.9 4.1 8.9

14.8 6.9 17.8

NS*** NS NS

Irrigation level (I) N rate (N) I×N

7 4 10

4.8 3.1 7.2

9.8 7.1 15.6

NS 2 NS

ETd1

ETd2

ETd3

ETd4

ETd5

2012–13

ETm

ETd1

ETd2

ETd3

ETd4

ETd5

42.7 a 44.0 a 43.3 a – 43.3 a 46.7 a 41.7 a 42.3 a 42.3 a 39.0 a 37.7 a 41.7 a 37.8 a 40.3 a 39.7 a 36.3 a 38.7 a 35.0 a 32.0 a 41.2 a 44.4 a 43.2 a 41.8 a 45.3 a 43.1 a 41.6 a 45.5 a 43.1 a 41.7 a 45.3 a 42.2 a 39.5 a 41.3 a 40.5 a 40.5 a 40.3 a 36.5 a

LSD 5% 2011–12

2012–13

* ** ***

ETm, ETd1,ETd2,ETd3,ETd4 and ETd5 represent irrigation at 100, 90, 80, 70, 60 and 50% ETc, respectively. Within a column for each year, means followed by the same letter/s are not significantly different at the = 0.05 level by LSD test. NS means non-significant at the P = 0.05 level.

increased N availability and greater growth (Table 2) with N application (Rathore et al., 2016). The NU under different N rates varied with irrigation levels. A significant increase in TNU was recorded up to N120 with ≥ETd2, up to N80 at ETd3, and up to N40 at ≤ETd4 irrigation levels. The NUE parameters (AEN , REN and PEN ) declined with a decrease in irrigation levels and rise in N rates in both years (Table 6). Averaged across years and N rates, ETd5 had 67, 64 and 9% reduction in AEN , REN and PEN , respectively. The higher NUE at

higher levels of irrigation might be attributed to the better N mineralization and least nitrogen loss through leaching and volatilization at optimum soil moisture condition ultimately leading to better plant uptake of N and hence growth and yield (Bandyopadhyay et al., 2010). The better growth as evident from the higher leaf area and dry matter (Table 2), and better partitioning of biomass to sink as evident from higher yield components (Table 3) is a possible explanation for higher AEN and REN with full irrigation and moder-

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ate water deficit irrigation treatments compared to severe deficit irrigation (ETd4 and ETd5) levels observed in this study. The NUEs declined with a rise in N rates. The I × N interaction effects had significant effects on AEN and REN . The AEN and REN were greater among N rates at ≥ETd2 irrigation levels compared to their respective values with ≤ ETd3 irrigation levels in both years. The AEN ranged from 19.1 to 32.3 kg grain kg N −1 in 2011–12 and from 24.6 to 37.0 kg grain kg N −1 in 2012–13 among N rates at ≥ETd2 irrigation levels, while at ≤ ETd3 irrigation levels, the AEN ranged from 2.5 to 22.1 kg grain kg N−1 , and from 4.9 to 25.3 kg grain kg N−1 in the respective years. The results of the present study are in agreement with the findings of Pradhan et al. (2014) and Rathore et al. (2016). The decrease in AEN and REN with an increase in N rates might be attributed to greater losses of N at higher levels of N, and to the fact that N uptake and yield of wheat did not increase with the same proportion as the N fertilizer application. 4. Conclusions Irrigation levels and N rates are two of the most important factors for optimizing yield, water productivity and nitrogen-use efficiency of wheat in arid regions. The moderate deficit irrigation ETd2 had greatest water productivity with about 17% of irrigation water use and only 5% reduction in grain yield compared to full irrigation. The high water productivity indicated a definitive advantage of employing sustained moderate deficit irrigation (applying 80% water of full irrigation throughout the growing season) in sprinkler irrigated wheat under limited water supply conditions. The study demonstrates that yield and water productivity were determined not only by irrigation levels, but also by their interaction with N rates. There was an optimal level of N for each level of irrigation. Therefore, for arid regions where water is a limiting factor and the wheat crop is normally fully irrigated, the amount of N fertilizer that will be applied should be adjusted to the amount of water that is available for the irrigation. Differential N rates at different water supply offer farmers and irrigation system managers an opportunity to make wheat production more profitable by using different rates of fertilizer in different sectors of the irrigated perimeters. This study indicated that optimization of irrigation and N rates can significantly improve yield, water productivity and nitrogen use efficiency of wheat in arid regions. Further study is needed to evaluate the performance of deficit irrigation with different cultivars, soil moisture conservation options (tillage, planting methods, mulching), and N management strategies (splitting of N). Acknowledgement This study was financially supported by ICAR-CAZRI Institute Project CAZRI/T04/40. References Ali, M.H., Hoque, M.R., Hassan, A.A., Khair, A., 2007. Effect of deficit irrigation on yield, water productivity and economic return of wheat. Agric. Water Manage. 92, 151–161, http://dx.doi.org/10.1016/j.agwat.2007.05.010. Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop Evapotranspiration. FAO Irrigation and Drainage Paper 56. Food and Agriculture Organization of the UN, Rome. Amir, J., Krikun, J., Orion, D., Putter, J., Klitman, S., 1991. Wheat production in an arid environment. I. Water-use efficiency, as affected by management practices. Field Crop Res. 27, 351–364, http://dx.doi.org/10.1016/03784290(91)90041-S. Bandyopadhyay, K.K., Misra, A.K., Ghosh, P.K., Hati, K.M., Mandal, K.G., Mohanty, M., 2010. Effect of irrigation and nitrogen application methods on input use efficiency of wheat under limited water supply in Vertisol of Central India. Irrig. Sci. 28, 285–299, http://dx.doi.org/10.1007/s00271-009-0190-z. Braun, H.J., Atlin, G., Payne, T., 2010. In: Reynolds, M.P. (Ed.), Multi-location Testing as a Tool to Identify Plant Response to Global Climate Change. Climate change and crop production. CABI Climate Change Series, Surrey, pp. 115–118, http:// dx.doi.org/10.1079/9781845936334.0115.

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