Rice optimal water use in different air temperatures at flowering, nitrogen rates and plant populations.

Present study was conducted to determine optimal amounts of irrigation water for rice in different nitrogen application rates, flowering stage air temperatures, T(f) and plant populations. The results indicated that in water limiting conditions in the study area, the optimum irrigation water was affected by crop management (N application rate and plant population) and climatological factors such as T(f). The optimum amounts of water, w(w) decreased at a higher rate (from 1988 to 1226 mm) by increase in nitrogen application rate (from 0 to 150 kg N ha(-1)) at higher T(f) and plant population. These values were 2692 to 2191 mm of water for 0 to 150 kg N ha(-1) for low value of T(f) and plant population. Under unfavorable air temperature condition and low plant population, the w(w) decreased by 19% at 150 kg N ha(-1), compared with 0 kg N ha(-1). However, under favorable air temperature condition and high plant population, this value was 38%. Therefore, under water limiting conditions in the study area, the higher plant population and favorable climatological factor can highly reduce the optimum irrigation water at higher N application rate. Also, N application rate, plant population, P, air temperature at the flowering stage and applied irrigation water affected the net income. The maximum net income was obtained in T(f) = 28.2 degrees C (near optimum air temperature during the flowering stage, 30-33 degrees C), P = 25 hills m(-2), 120 kg ha(-1) N application and 2138 mm applied irrigation water. The field management factors such as applied irrigation water, nitrogen application rate and plant population can be controlled by field manager and the optimum amounts may be applied. However, the climatological factors are unpredictable, therefore, these factors should be considered in economic analysis of crop yield production and field management.