Masoud Mohammadi; Bijan Ghahreman; Kamran Davari; Majid Vazifehdoost; Hamideh Noori
Abstract
Field studies to determine optimum amount of water required for maximum production are time-consuming and expensive. Therefore, in this study the agro-hydrological model SWAP 3.03 was used to simulate winter wheat yield under different qualities and quantities of irrigation water and to determine water-salinity-yield ...
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Field studies to determine optimum amount of water required for maximum production are time-consuming and expensive. Therefore, in this study the agro-hydrological model SWAP 3.03 was used to simulate winter wheat yield under different qualities and quantities of irrigation water and to determine water-salinity-yield optimum function. Irrigation treatments consisted of four water salinity levels (S1=0.7, S2=2, S3=4 and S4=6 dS/m), three amounts of water (W1=80, W2=100, and W3=120 mm), and six levels of management allowed depletion (MAD1=0.3, MAD2= 0.4, MAD3= 0.5, MAD4= 0.6, MAD5= 0.7 and MAD6= 0.8). Yield and water use efficiency values were determined in different modes and the best MAD value obtained was 0.5. Yield data were fitted to different forms of production functions (simple linear, logarithmic linear, quadratic and transcendental) and the best one was established based on sensitivity analysis. The maximum grain yield (6619 kg/ha) corresponded to W1S1MAD2 treatment and the minimum yield (2048 kg/ha) corresponded to W1S4 MAD3 treatment. The results showed that the quadratic production function was optimal for production and could be recommended. Investigation of the maximum values of error (ME) showed that the logarithmic linear and simple linear functions had the highest error. In the irrigation treatments, W1S1MAD3 and W1S1MAD4 with 0.61 kg /m3 had the highest water use efficiency. However, water use efficiency decreased when water stress and salinity increased. The iso-yield curve showed that by increasing amounts of irrigation, more saline water could be applied without a change in yield.