Determination of yield - water use function for sugar beet in Qazvin

The purpose of this study was to determine yield-water use function of sugar beet in Qazvin city, and evaluation of empirical yield functions. The experiment was conducted at Feizabad Research Station for three years. Treatments were composed of four irrigation levels including 60 (E1), 90 (E2), 120 (E3) and 150 (E4) mm evaporation from class A pan, respectively. Since the effect of year on crop yield was significant, the treatments were labelled from T1 to T11 to compare the crop yield response coefficient based on monthly function. Results showed that the water requirement of sugar beet was equal to 1028 mm across the growth period with treatments T1 (74680 kg/ha) and T2 (23000 kg/ha) having the maximum and minimum yields, respectively. According to the statistical correspondence, the “proposed method” which estimates the amount of product response coefficient on the basis of monthly function, yielded the least root mean square of standard error (RMSE) and normalized root mean square of standard error (NRMSE) and as well as the highest agreement index (d) and correlation coefficient (R2). As a result, the monthly power function method is recommendable. Using monthly function method, the crop yield response coefficient for April, May, June, July, August and September was equal to 0.6, 0.6, 1.35, 1.35, 0.83 and 0.6, respectively and for the initial growth, development, Middle, and final growth stages was to 0.6, 0.8, 1.35 and 0.6, respectively with an average of 0.89 for the total growth period. Finally, using the monthly function and coefficients, an optimal water distribution program for various conditions of water shortage was presented.