Determination of the yield response factor to water (Ky) and the best function of water-salinity-yield of turnip in Kashmar

In order to adapt to water scarcity, various strategies can be proposed and implemented including; the adoption of appropriate policies for optimizing water use through the determination of optimal production functions. Water scarcity and a decreasing in the quality of water and soil resources in the country are among the main causes of production decline. Hence, this study was conducted to determine the sensitivity coefficients of plant and optimum water-salinity-yield function for turnip in Kashmar. A factorial experiment was conducted in a completely randomized design with three replications including two factors salinity and irrigation water. Four levels of irrigation water salinity were, drinking water: S1 = 0.7, S2 = 4, S3 = 8 and S4 = 12 dS/m3, and three levels of irrigation water, including: full irrigation (100% water requirement) = W1, W2= 75 % W1 and W3 = 50% W1, applied to a sandy-loam soil texture. Functional data were fitted to different forms of production functions (linear, logarithmic, quadratic and exponential), and after sensitivity analysis, the optimum production function of turnip was determined. Then the water use efficiency and the sensitivity coefficients of the plant were determined. The results of the sensitivity analysis indicated that the quadratic production function for turnips as the optimal production function is recommended. The study of maximum error (ME) showed that the most error is related to simple logarithmic and linear functions. The Control treatment (W1S1) and W2S1 treatment (75% water requirement) were the highest yield with 6.66 and 7.24 kg/m3, respectively, but the water productivity decreased with increasing water stress and salinity. The average amount of crop yield response factor (Ky) was estimated at the rate of 1.73 in the salinity and water stress combination. Also, the sensitivity coefficient (Ks) decreased with increasing salinity and water stress and the lowest value of (Ks) belonged to W3S4 treatment at the rate of 0.5. The same product curves demonstrate that with an increasing amount of irrigation water, higher saline irrigation water can be used for turnip, which the yield does not change.