Evaluation of production functions to estimate potato yield in different irrigation treatments

Water use in field is expressed as evapotranspiration (ET). If the water requirement of the plant is not provided, the rate of plant evapotranspiration is less than potential evapotranspiration and water stress occurs and plant yield decreases. In order to prevent the loss of plant yield, limited water resources should be optimized based on the inevitable needs of the plant. One of the methods for optimal use of water in the agricultural sector is to increase the efficiency and use of water in the production of agricultural products such as potatoes through the production functions and the relative relation of yield and water consumption. The objective of this study was to evaluate the production functions has been modified by Rase (2004) and Tafteh et al. (2013) for estimating potato yield under deficit irrigation conditions. For this purpose, an experiment was conducted in a randomized complete block design with five treatments and three replications for two years of cultivation and total of 30 treatments at Shahrekord Agricultural Research Center. Irrigation treatments were in five levels of full irrigation (E0), 85% (E1), 70% (E2), 55% (E3) and 30% (E4) of actual evapotranspiration of potato from drainage lysymeter, at different stages of plant growth Includes seed stage and vegetative growth (T1), full growth stage (T2), and stage of ripening of the tubers (T3). The results showed that the highest water requirement was 814 mm and was related to T16 treatment with a maximum yield of 42500 kg/ha and the minimum water consumption was 512 mm and was related to T15 treatment with a yield of 24600 kg/ha. After estimating the product yield using Reese (2004) and tafteh et al (2013) methods, the performance of these two functions was compared with the measured yield on the field. In the first method, the RMSE, NRMSE values were 7113 and 0.19, and in the second method, the values of these statistics were 6830 and 0.18, respectively. Both methods were overestimated based on MBE index and Tafteh et al. (2013) method with FAO coefficients had the lowest MBE. Therefore, using this method, the values of the sensitivity coefficient were calibrated and finally the yield response factor were obtained based on Tafteh et al function for 4 phases of the FAO standard (initial, development, middle and final) 0.29, 1.12, 0.95 and 0.46 respectively.