Optimization of Deficit Irrigation and Nitrogen Rates on Bread Irrigated ...

International Journal of Agriculture and Crop Sciences. Available online at www.ijagcs.com IJACS/2012/4-22/1681-1687 ISSN 2227-670X ©2012 IJACS Journal

Optimization of Deficit Irrigation and Nitrogen Rates on Bread Irrigated Wheat at Northwest of Iran Ali Reza Tavakoli1*, and Mehran Mahdavi Moghadam2 1. Assistant professor of Agricultural Engineering Research section, Agricultural Research Center of Semnan Province (Shahrood), Shahrood, Iran 2. Department of Irrigation and Drainage, College of Abouraihan University of Tehran * Corresponding author email: Ali Reza Tavakoli, [email protected] ABSTRACT: Limitation of water resources, relative much land and little of water productivity (WP) are the specifications of agricultural irrigated areas. So, optimization of WP and expanding cropping area, led to improve WP and increase total wheat production. This field experiment (during 20002002) on a deep clay silty soil in Northwest of Iran was conducted for four deficit irrigation levels (rainfed, 1/3, 2/3 and full irrigation) combined with N rates (0, 30, 60, 90 and 120kg.N.ha-1) on Alamout wheat variety. With irrigation and nitrogen, crop responses were generally significant up to 90kg.N.ha-1. An addition of 34 percent reduction of water use related to full irrigation (2/3 of F.I) significantly increased yields and obtained maximum water productivity. Use efficiency for both irrigation water and N levels were greatly increased by deficit irrigation. Nitrogen use efficiency (NUE) over two crop seasons increased from 2.63-25.04 kg.N-1.ha-1 for grain yield. The WPirr over two seasons increased from 15.08-27.92 kg.mm-1.ha-1 for total grain yield and 8.43-20.56kg.mm-1.ha1 for increase grain yield compare to rainfed condition. Optimum level of deficit irrigation was realized with 2/3 of full irrigation treatment (27.3 percent decreases in full irrigation water use = 160mm) which led to maximum irrigation water productivity and with 4467kg.ha-1 grain yield. Water productivity based on irrigation water alone (WPirr) and both irrigation plus rainfall (WPrain+irr) at 90kg.N.ha-1 over the two seasons were 9.58 and 27.92kg mm-1 respectively. Although it reduced 19.8 percent of grain yield comparison with full irrigation, but it got maximum water productivity, 37.5 percent increase in cropping area and mentioned 10.2 percent increase in total yield production. Thus, with 66% of full irrigation and 90kg.N.ha-1, combined with appropriate management, wheat output could be substantially and consistently increased in the semi arid climate zone. Keywords: Bread wheat, Water productivity, Nitrogen, Yield components INTRODUCTION Bread wheat (Triticum aestivum L.) is one of the most important food crops and is extensively grown throughout the dry areas in Iran. Precipitation is extremely variable, from year to year and within season, and can range from 50 to 1200 mm per year. Both rainfall and temperature dictate crop growth duration and cropping patterns. Cropping systems change in response to variation in elevation, rainfall and water resources. The foremost concern in arid and semiarid areas is moisture availability and its efficient use. Crop yields under arid and semi arid areas conditions are related to seasonal rainfall (amount and pattern), irrigation water (quality and quantity) and farmer agronomic management, then water productivity can be substantially improved by crop management practices (Tavakoli et al., 2010; Cooper and Gregory, 1987; Keating et al., 1986; Haris et al., 1991),fertilizer use (Harmsen, 1984; Keating et al., 1985; Ryan and Matar, 1992) and agronomic management (Tavakoli et al., 2010). Wheat production and water productivity under irrigated conditions are low and subject to substantial year to year fluctuation due to erratic rainfall and poor irrigation and agronomic management. Deficit irrigation can be considered as a key strategy for increasing on-farm water productivity in water-scarce dry areas (Zhang, 2003). In north Syria, wheat has water a productivity of applied water (1 kg m-3) twice as high as grain-legume crops (0.4– 0.5 kg m-3) (Zhang and Oweis, 1999; Zhang et al., 2000). Among agronomic practices, applications of nitrogen and deficit irrigation are widely recognized as a means of increasing wheat yield in the dry areas (Cooper et al., 1987; Siddique et al., 1990; Anderson and Smith, 1990; Oweis et al., 1998). The introduction of deficit irrigation (30-50 percent reduction water use related to full irrigation) to winter cereals can potentially stabilize and increase yields, as well as increasing the use

Intl J Agri Crop Sci. Vol., 4 (22), 1681-1687, 2012

efficiency of water received both from rainfall and from irrigation (Oweis et al., 1992; Hang and Miller, 1983; Shearer, 1978; English, 1990; English and Raja, 1996, Janbaz and Fardad, 1996; Tavakoli, 2004, 2006a, and 2006b). Nitrogen deficiency, after drought, is the major constraint in dryland cereal farming (Campbell et al., 1993). Within the Mediterranean areas, N deficiency is ubiquitous, being extensively reported from Morocco (Mossedaq and Smith, 1994; Ryan et al., 1992; Shroyer et al., 1990) to Syria (Anderson, 1985; Harmsen, 1984) and indeed in many countries of the region (Ryan and Matar, 1992). As fertilizer N responses are directly related to rainfall and amounts of soil water storage, N use should be correspondingly greater, when deficit irrigation is also applied. However, the response of wheat to irrigation water is dependent on the cultivar (Fischer and Maurer, 1978; Sojka et al., 1981; Nachit et al., 1992; Tavakkoli and Oweis, 2004). Thus, potential yield in any environment depends not only on water and N (Aggarwal and Kalra, 1994), but on cultivars as well (Anderson, 1985; Guy et al., 1995; Tavakoli et al., 2005). Objective of this study was to optimization of irrigation water use, improving water productivity and to identify the optimum rates of nitrogen technology package the efficiency of water and other inputs. MATERIALS AND METHODS Research Site The experiment was conducted in two cropping seasons (2000-2002) at Maragheh, main station of Dryland Agricultural Research Institute (DARI), in North West of Iran (37º 15' N; 46º 15' E; elev. 1725m), with a long-term annual rainfall of 342 mm (1983-2001). Soil The soil at Maragheh station is deep and classified as fine clay (fine mixed active mesic vertic calcixerpts). Relevant properties were: pH, 7.7; EC, 0.61dS/m; Extractable K, 662 ppm; Extractable P, 16.3 ppm; Total N, O.C. and T.N.V., 0.055, 0.65 and 4.2%, respectively; and sand, silt and clay, 160, 410 and 450gr.kg-1, respectively. Soil moisture at field capacity (-30kpa) and at wilting point (-1500kpa) was about 380 and 200 mL.L-1, respectively. Weather Over the study period, growing season rainfall was 228mm (2000-2001), 382mm (2001-2002). The first season’s rainfall was below the long-term average (342mm), with the first rain on 23-25 October; 17.4mm rainfalls was well to germination and continue growth at autumn (Table 1). The rainfall in the second year was above normal but the first season’s rainfall was 5 November and very late (Table 1), rainfed treatment cannot to germination and growth. However, 49.5mm rainfall in May made a substantial contribution to crop yield, irrigation and rainfed treatments, in addition to the cooler weather in spring. Rainfall is inversely related to seasonal temperatures. a

Table1. Weather parameters at Maragheh research station, northwest of Iran Season 2000/2001

Parameter P (mm) ° Tmax ( C) ° Tmin ( C) RH (%)

Oct. 21.9 15.7 4.1 56.0

Nov. 22.6 8.4 -1.4 71.0

Dec. 28.6 3.9 -4.3 76.0

Jan. 4.5 2.6 -10.4 66.0

Feb. 14.5 2.6 -5.6 52.9

March 48.9 13.8 -0.9 51.2

April 21.8 16.4 2.8 51.1

May 32.8 21.9 6.4 42.9

June 0.0 30.4 12.1 28.6

July 31.6 30.0 14.6 35.1

Aug. 0.4 32.0 14.8 28.9

Sep. 0.2 26.4 11.4 32.8

2001/2002

P (mm) ° Tmax ( C) ° Tmin ( C) RH (%)

9.4 18.0 6.4 49.8

35.5 11.6 -2.4 67.0

50.5 4.1 -2.5 79.5

74.0 2.4 -11.2 80.0

13.2 4.6 -8.8 68.0

39.0 10.2 -4.2 59.0

109.5 11.8 2.3 69.0

49.5 21.7 4.7 55.0

1.2 27.1 9.6 30.0

0.0 30.8 15.9 37.0

0.0 28.4 14.5 33.6

0.0 26.4 10.6 26.5

long-term

P (mm) ° Tmax ( C) ° Tmin ( C) RH (%)

10.6 21.9 3.7 50.4

26.2 13.5 -3.9 66.9

27.2 9.3 -10.7 72.6

48.8 4.7 -13.7 73.7

24.7 4.6 -17.5 66.9

51.6 13.8 -10.8 63.1

56.0 18.3 -0.9 56.8

27.6 22.6 3.9 50.6

2.6 30.4 9.6 36.7

8.8 31.9 14.2 40.4

1.8 32.0 13.2 35.8

1.3 26.7 8.8 37.9

a Precipitation (P), Maximum and Minimum temperatures (Tmax, Tmin) and mean monthly relative humidity (RH) for the two study seasons and for long-term.

Produce The treatments included four levels of deficit irrigation (i.e. full irrigation, or 100% of crop water requirements, and 1/3 and 2/3 of that amount, as well as rainfed conditions), five N rates (0, 30, 60, 90 and 120kg.N. ha-1), on one bread wheat cultivar (Alamout). A split plot design with three replicates was used. Dates of sowing (12-14 October) were about two weeks before the first rainfall (based on long-term climate data) (Tavakoli et al., 2003). Water levels were represented by the main plots and N rates by subplots. The site 1682


changed each year between two adjacent blocks the cereal – fallow. A surface irrigation system (small basins) was designed and distributed with linear hand move polyethylene pipes at small basin areas (4m*5m), along polyethylene pipe, which were 4m long and 63mm in diameter. Spacing between holes along distributive pipe were 2.5cm. The source of the irrigation water was groundwater, of good quality: PH, 7.6; EC, 1ds/m and SAR, 1.5. Water was applied to all treatments at the same time: i.e., when the root zone of the full irrigation treatment had lost 50% of its available moisture. The amount of water, which was then given to full irrigation treatment, was calculated to restore root zone moisture to field capacity. The other treatments received fixed proportions (1/3 and 2/3 of the full irrigation treatment). Details regarding the amount of irrigation water applied and the application dates for each season are presented in Table 2. Soil moisture was measured weekly, before and after water application, using TRIME probes (TDR groups, Time Domain Reflectometer), these had access tubes inserted to 80 cm depth in two replicate representing all five N rates. Table2. Irrigation amount and application dates for bread wheat trials at Maragheh, Iran, 2000-02 2000/2001 Irrigation date 15 Oct. 21 April 15 May 29 May

First irrigation Second irrigation Third irrigation Fourth irrigation Total irrigation water (mm) Precipitation (mm) Total water received (mm)

1/3 (mm) 40 24 24 24 112 228 340

2/3 (mm) 40 48 48 48 184 228 412

Full Irr. (mm) 40 72 72 72 256 228 484

2001/2002 Irrigation date 13 Oct. 22 May 7 June none

1/3 (mm) 40 24 24 none 88 382 470

2/3 (mm) 40 48 48 none 136 382 518

Full Irr. (mm) 40 72 72 none 184 382 566

The crop was planted in 20 cm rows at seed rates was approximately 400seeds.m-1. The N application was split, half at planting and half top – dressed at the early spring. Measurements included: grain and straw yield, biomass, 1000KW, Plant height, kernel number per spike, spike number per squire meter and harvest index. Analysis of variance (ANOVA) was used to assess, statistical significance using a block structure, treatment structure and ANOVA commands set in MSTATC and SPSS program. RESULTS The analysis of variance (Table 3) showed that, during the two seasons of the study, there were significant effects due to the primary factors and their interactions. However, the effects were more consistently expressed for grain (kg.ha-1), straw (kg.ha-1), biomass (kg.ha-1), harvest index (%), 1000KW (gr), plant height (cm), spike number per squire meter and kernel number per spike. Table3. Mean squares of the effect of Irrigation and Nitrogen rates on agronomic parameters of irrigated wheat (2000-2002) Source of variation Year Error Irrigation (I) I× Y Error Nitrogen (N) N×Y I×N I×N×Y Error C.V (%)

df. 1 4 3 3 12 4 4 12 12 64

1000K.W ns

73.79 18.73 ** 132.0 ** 70.78 1.375 ** 17.25 ** 40.28 ** 4.403 ** 7.962 1.640 4.07

ns: Non significant.

Spike per squire meter ns 8036 2951 ** 285337 ns 9885.2 3384.8 ** 31722 ns 921.3 ns 3628.2 ns 2180.5 3064.8 16.7

Kernels per Spike ** 3683 55.8 ** 745.2 ns 51.74 100.2 ns 81.83 * 127.1 ns 62.98 ns 49.62 39.63 22.21

Plant Height ns 2493 1091 ** 9077 ** 252.9 25.3 ** 643.4 ** 101.4 * 99.97 * 41.87 44.26 8.94

*: Significant at the 5 % level of probability

Harvest Index ** 269 8.79 ** 1107 ** 141.2 21.6 ** 25.12 * 16.38 ** 58.92 * 13.83 5.99 7.76

Biomass **

173.8 1.402 ** 264.8 ** 29.97 4.407 ** 22.66 ** 8.057 ** 4.073 ** 1.779 0.499 7.74

Straw **

63.84 0.974 ** 73.59 ** 17.71 2.742 ** 10.61 ** 3.123 ** 1.042 ** 0.973 0.378 10.08

Grain Yield ** 26.96 0.115 ** 60.24 * 1.572 0.381 ** 2.659 ** 1.407 ** 1.448 ** 0.321 0.065 8.46

**: Significant at the 1 % level of probability

Differences due to year, irrigation and nitrogen were highly significant for all variables, except N rates on kernel number per spike. In addition, the interactions of N with year were significant for all variables, except on spike number per M-2. Similarly, there were significant interaction between “irrigation level with N rates”, “irrigation level with year” and between “irrigation level, N rates and year” for all variable, except on kernel number per spike and spike number per squire meter. Grain yield and yield components As the main production factor in irrigated cropping is water, whether from rainfall and added as irrigation, the interaction involving water, year and nitrogen are depicted (Fig 1). Addition of irrigation increased crop yields in each season, but the effect varied with the season. Thus the highest yields were in second season (2001-2002) and the lowest yields in first season (2000-2001). 1683


Yields from rainfall plots alone were poorly related to seasonal rainfall. Regardless of season, the pattern of response to deficit irrigation was similar, but as well, with the addition of the first increment of water having the greatest effect. While further increases occurred at the 2/3 of full irrigation level, there was non significant at additional increase with full irrigation (Fig. 1c). The response to N was conditioned by water levels (Fig.1a,b,d,f). As expected, the lowest response to N was under rainfed conditions, with no increase beyond the 30kg.ha-1 on dry years or delay first effective rainfall at autumn, the highest level (more 120kg.N.ha-1) tended to decrease yields. As the N application rate increased, the effect on yield was limited by water (at 1/3, the lowest irrigation rate) response to N were not limited by available water at the 2/3 of full irrigation level, as they were similar to those at full irrigation, but the highest level (120kg.N.ha-1), tended to decrease yields (Table 4). Under any soil water condition, delay in seed germination at autumn, on all treatments, reduced the extent of a yield response to added N. N

N

N

N

I

I

I

I

b

a

Grain yield (kg/ha)

Grain yield (kg/ha)

N

I

I

I

I

N

N

I

c

N

I

N

I

N

I

Straw (kg/ha)

Grain yield (kg/ha)

d

I

I

I

I

I

I

I

N

N

N

N

N

N

N

N

I

f Biomass (kg/ha)

Grain yield (kg/ha)

e

N

N

N

N

N

N

N

Figure.1 Bread wheat grain yield as a function of deficit irrigation and nitrogen at two years

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Table4. Effects of irrigation and nitrogen on grain yield (ton/ha) at Maragheh, northwest of Iran Irr (mm) Rainfed I1/3 (100mm) I2/3 (160mm) I3/3 (220mm) Mean

N (kg/ha)

N0 1.464 j 2.476 i 3.064 gh 3.318 fg 2.580

N30 1.446 j 2.670 hi 3.540 ef 3.887 de 2.886

N60 1.354 j 2.724 hi 3.983 d 4.559 bc 3.155

N90 1.178 jk 2.713 hi 4.467 c 5.572 a 3.482

N120 0.796 k 2.319 i 4.049 d 4.919 b 3.021

Mean 1.248 D 2.580 C 3.820 B 4.451 A

Water Productivity The productivity of applied water (PAW) is defined as crop yield per unit volume of water use. Volume of water use refers to irrigation, rainfall and or sum of irrigation and rainfall amounts. After its maximum, PAW shows a decrease with increasing water supply, depending on the response of yield to water. The most productive use of water was reached with about 160mm of irrigation water use. The quadratic production function was used to describe the response of wheat yield to total applied water: WPirr = -1.947 + 0.058×N + 0.173×Irr -4.225×10-4×N2 + 4.489×10-4×Irr×N – 5.939×10-4×Irr2 Where WP is water productivity (kg.mm-1), Irr is the irrigation water use (mm), N is nitrogen rates (kg.ha1 ), and -1.947 is the regression coefficient. Fig. 2 shows the relationship between PAW and the levels of water application and nitrogen rates for wheat in northwest of Iran. The crop water productivity function in Fig. 2 was used to derive the productivity of the applied water. Deficit irrigation, nitrogen and their interaction affected on water productivity. The WPrain+irr, WPirr and nitrogen use efficiency (NUE) calculated for treatments averaged over the two seasons (Table 5). NUE over two seasons increased from 2.63 to 25.04kg.N-1.ha-1 for grain yield. The WPrain+irr over two seasons increased from 3.85 to 10.59kg.mm-1.ha-1 for grain yield by applying 90kg.N.ha-1 and maximum WPirr over two seasons was 20.56kg.mm-1.ha-1 for grain yield at applying optimum level of irrigation rate (2/3 of full irrigation) (table 5). Optimum deficit irrigation strategy allows one to apply 27.3% less irrigation water for a grain-yield loss of only 19.8%, but it got maximum water productivity (27.92kg.mm-1) and 37.5 percent increase in cropping area mentioned 10.2 percent increase in total yield production. WP amounts (kg/mm)

Figre.2 Relationship between irrigation WP and the amounts of water and nitrogen -1

-1

Table 5. Amounts of water productivity (kg.mm .ha ) under irrigation and nitrogen rates -1 a

N (kg/ha) N0 N30 N60 N90 N120

WP.irr (kg.mm ) (on increase yield compare with rainfed condition) F.I 66%F.I 33%F.I Rainfed 8.43 10.00 10.12 11.1 13.09 12.24 14.57 16.24 13.70 19.97 20.56 15.35 18.74 20.33 15.23 -

-1 b

-1 c

WP.irr (kg.mm ) (on total yield) F.I 15.08 17.67 20.72 25.30 22.36

66%F.I 19.15 22.13 24.71 27.92 25.31

WP.rain+irr (kg.mm ) (on total yield) 33%F.I 24.76 26.70 27.24 27.13 23.19

Rainfed -

F.I 6.31 7.39 8.67 10.59 9.35

66%F.I 6.57 7.60 8.48 9.58 8.69

33%F.I 6.10 6.58 6.71 6.68 5.71

Rainfed 4.78 4.72 4.42 3.85 2.60

Yield irr − Yield ra inf ed Yield Yield a ) WPirr = b ) WP irr = irr irr . + rain irr . Zhang and Oweis (1999) reported that the deficit irrigation strategy allows one to apply 40–70% less irrigation water for a grain-yield loss of only 13%. Similarly, English and Raja (1996) reported that deficit irrigation averaging 64% of full irrigation was found to be economically equivalent to full irrigation when water c ) WP irr + rain =

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was the limiting factor, and deficit irrigation in which only 30% of full irrigation was applied was found to be equivalent to full irrigation in land-limiting cases. Zhang (2003) showed that two-thirds of full irrigation increased water productivity by 19–28% for wheat and 8% for maize. DISCUSSION Notwithstanding the variation in annual rainfall, and therefore dryland crop yields, this 2-yr study demonstrated some important findings. Yields can be substantially increased and stabilized with optimal irrigation and fertilizer inputs, together with higher yield potential. While many of the previous studies in the Mediterranean zone have focused on individual components of cereal cropping, few have integrated these components into a technology package with potential for adoption. However, even when this technology package is applied, some year to year yield ceiling will occur due to factors such as cold and fungal disease, which are difficult to control. The most dramatic implication from this study is the saving in irrigation water with little loss in yield. In most cases, applying 2/3 of full irrigation with 90kg.N.ha-1 quadruple yield compared with rainfed conditions. Although it reduced 19.8 percent of grain yield comparison with full irrigation, but it got maximum water productivity. Such yield increases clearly support the findings of Stewart and Musick (1982) in favor of the potential for conjunctive use of irrigation and rainfall semiarid regions with a rainfall ranges as found in WANA. The strategy of applying restricted amounts of water at critical growth stages based on available soil moisture, as practiced in this experiment, is the essence of the concept of deficit irrigation. By combining rainfall and −1

deficit irrigation, the combined water productivity at 90kg.N.ha in terms of crop grain yield ranged from 6.68, 9.58 and 10.59kg of grain per mm of water (Precip.+ Irr.) at the 1/3, 2/3 and full irrigation levels, respectively. However, when separating the contribution of the two sources to crop grain yield, water productivity of deficit irrigation at 90kg.N.ha-1 ranged from about 15.35, 20.56 and 19.97 kg of grain per mm of water at the 1/3, 2/3 and full irrigation levels, respectively. Optimum level of deficit irrigation was realized with 2/3 of full irrigation treatment (27.3 percent decreases in full irrigation water use = 160mm) which led to maximum irrigation water productivity and with 4467kg.ha-1 grain yield. Water productivity based on irrigation water alone (WPirr) and both irrigation plus rainfall (WPrain+irr) at 90kg.N.ha-1 over the two seasons were 9.58 and 27.92kg mm-1 respectively. In addition, when the crop water productivity functions are known, it is possible to appropriately allocate limited water resources where irrigation strategy and nitrogen rate compete for scarce water in dry areas. ACKNOWLEDGMENTS This project funded by Dryland Agricultural Research Institute (DARI) of Islamic Republic of Iran and we thank Mr. A. Haghighati-Maleki and Dr. B. Abdol-Rahmani researcher staffs of DARI, Dr. M. Pala and Dr. T. Oweis from International Center for Agricultural Research in Dry Areas (ICARDA). REFERENES Aggarwal PK, Karla N. 1994. Analyzing the limitations set by climatic factors, genotype, and water and nitrogen availability on productivity of water: II. Climatically potential yields and management strategies. Field Crops Research, 38: 93-103. Anderson WK, Smith WR.1990. Yield advantage of semi dwarf compare to tall wheat depends on sowing time. Australian J. Agricultural Research, 41: 811-826. Anderson WK. 1985. Differences in response of winter cereal varieties to applied nitrogen in the field: I. Climatically potential yields and management strategies. Field Crops Res. 11: 363-367. Campbell CA, selles F, Zentner RP, McConkey BG. 1993. Available water and nitrogen effects on yield components and grain nitrogen of zero–till spring wheat. Agronomy J.85: 114-120. Cooper PJM, Gregory PJ, Tully D, Harris H. 1987. Improving water –use efficiency in the rainfed farming systems of West Asia and North Africa. Exp. Agriculture, 23: 113-158. Cooper PJM, Gregory PJ. 1987. Soil water management in the rainfed farming systems of the Mediterranean region. Soil Use Management, 3(2): 57-62. English MJ, Raja SN. 1996. Perspectives of deficit irrigation. Agric. water Mang. 32:1-14. English MJ. 1990. Deficit irrigation: Analytic framework .J. of ASCE (IR), 116(3): 399-412. Fischer RA, Maurer R. 1978. Drought resistance in spring wheat cultivars: I. Grain yields responses. Australian J. Agricultural Research, 29: 897-912. Guy SO, Tablas–Romero H, Heikkinen MK. 1995. Agronomic responses of winter wheat cultivars to management systems. J. Prod. Agric. 8: 529-535. Hang AN, Miller DE. 1983. Wheat development as effected by deficit irrigation frequency sprinkler irrigation. Agroomy J. 75: 234-239. Harmsen K. 1984. Nitrogen fertilizer uses in rainfed agriculture. Fert. Res.5: 371-382. Harris HC, Cooper PJM, Pala M. 1991. Soil and crop management for improved water use efficiency in rainfed areas. Proc. Int. Workshop, Ankara, Turkey. 15-19 May 1989. ICARDA, Aleppo, Syria. Janbaz HR, Fardad H. 1996. Effects of water stress and interval irrigation on wheat in Karaj region (Iran), MSc thesis of Tehran University. (in Persian) Keating JDH, Dennett MD, Roadgers J. 1986. The influence of precipitation regime on the management of dry areas in northern Syria. Field Crops Res. 13: 239-249.

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Intl J Agri Crop Sci. Vol., 4 (22), 1681-1687, 2012 Keating JDH, Neate PJH, Shepherd KD. 1985. The role of fertilizer management in the development and expression of crop drought stress in cereals under Mediterranean environmental conditions. Exp. Agric. 21: 204-222. Mossedaq F, Smith DH. 1994. Timing nitrogen application to enhance spring wheat yields in a Mediterranean climate. Agronomy J. 86: 221-226. Nachit MM, Sorrells ME, Zobel RW, Gauch HG, Fischer RA, Coffman WR. 1992. Association of environmental variables with sites means grain yield and components of genotype environment interaction in durum wheat: II.J. Genet. Bread. 46: 369-372. Oweis T, Pala M, Ryan J. 1998. Stabilizing rainfed wheat yields with supplemental irrigation and nitrogen in a Mediterranean climate.Agronomy J. 90:672-681. Oweis T, Zeidan H, Taimeh A. 1992. Modeling approach for optimizing supplemental irrigation management .Proc. International Conference on Supplemental Irrigation and Drought Water Management, Bari, Italy. Ist. Agron. Mediterraneo, CIHEAM/MAI-B, Bari. Ryan J, Abdel-Monem M, Shroyer JP. 1992. Using visual assessment of nitrogen deficiency in dryland cereals as a basis of action in Morocco. J. Nat. Resour. Life Sci. Educ. 21: 31-33. Ryan J, Matar A. (Eds). 1992. Fertilizer use efficiency under rainfed agriculture in West Asia and North Africa. ICARDA. Aleppo, Syria. Shearer MN. 1978. Comparative efficiency of irrigation systems. Proc. Annual Tech. Tonf. 183-188. Shroyer JP, Ryan J, Abdel-Monem M, El-Mourid M. 1990. Production of fall-planted wheat in Morocco and technology for its improvement. J. Agron. Educ.19: 32-40 Siddique KHM, Tennant DW, Perry M, Belford RK. 1990. Water use and water use efficiency of old and modern wheat cultivars in a Mediterranean type environment. Aust. J. Agric. Res. 41: 431-447. Sojka RE, Stolzy LH, Fischer RA. 1981. Seasonal drought response of selected wheat cultivars. Agron. J. 73: 838-845. Stewart BA, Musick JR. 1982. Conjunctive use of rainfall and irrigation in semi-arid regions. Adv. Irrig.1: 1-24. Tavakkoli AR, Oweis T. 2004. The role of supplemental irrigation and nitrogen in producing bread wheat in the highlands of Iran. Agric. Water Manage. 65(3): 225-236. Tavakoli AR, Belson V, Ferri F, Razavi R. 2003. Response of rainfed wheat to supplemental irrigation and nitrogen rates. Final research report, Dryland Agricultural Research Institute (DARI), Maragheh, Iran. (in Persian) Tavakoli AR, Oweis T, Ashrafi Sh, Asadi H, Siadat H, Liaghat A. 2010. Improving rainwater productivity with supplemental irrigation in upper Karkheh river basin of Iran. International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria, 123pp. Tavakoli AR, Oweis T, Ferri F, Haghighati A, Belson V, Pala M, Siadat H, Ketata H. 2005. Supplemental Irrigation in Iran: Increasing and Stabilizing Wheat Yield in Rainfed Highlands. On-Farm Water Husbandry Research Report Series No.5. 46pp, ICARDA. Tavakoli AR. 2004. An Economic Evaluation of Supplemental Irrigation at Optimum Rate of Nitrogen on Wheat in Rainfed Condition. J. of Agric. Eng. Res. 5(20): 86-97. (in Persian). Tavakoli AR. 2006b. Estimation of wheat production function and optimization of deficit irrigation and nitrogen. Pajouhesh-va-Sazandegi, in Agronomy & Horticulture, No 71, accepted. (in Persian) Zhang H, Oweis T. 1999. Water-yield relations and optimal irrigation scheduling of wheat in the Mediterranean region. Agric. Water Manage. 38: 195-211. Zhang H, Pala M, Oweis T, Harris H. 2000. Water use and water use efficiency of chickpea and lentil in a Mediterranean environment. Aus. J. of Agric. Res. 51: 295-304. Zhang H. 2003. Improving water productivity through deficit irrigation: Examples from Syria, the North China plain and Oregon, USA. PP. 301-309. In: Kijne, J.W., Barker, R. and Molden, D. (Eds.), Water Productivity in Agriculture, Limits and Opportunities for Improvement, International Water Management Institute (IWMI), Colombo, Sri Lanka.

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