INFLUENCE OF IRRIGATION INTERVAL AND POTASSIUM FERTILIZATION ON WATER PRODUCTIVITY OF SESAME Sesamum indicum L. UNDER SULAYMANIYA CONDITIONS

Abstract

This study was performed to test the influence of irrigation interval under different levels of potassium fertilization on water productivity of sesame (Sesamum indicum L.) crop for two growing seasons (2011 and 2012) under Sulaimaniya conditions. The main objective of this study was to select the appropriate irrigation interval and irrigation requirements to acceptable values so that maximum water saving can be achieved with minimum yield lost. Also, the role of K fertilizer in reducing water stress with the increase of the time of irrigation periods. Some empirical models (linear, parabolic, exponential and power function) were used to evaluate the crop responses to irrigation quantity and/or actual ET (ET_a). Completely Randomized Block Design was used in this experiment. The treatments (main plots) were six irrigation intervals (namely; 5, 10, 15, 20, 25, and 30 days), with three replications. Potassium fertilizer levels (namely; 0, 100, 200 and 300 kg K ha^-1) were implemented in subplots. Water was applied to plants by using drip irrigation system of 1.2 liters/hr per dripper. Seeds weight and actual evapotranspiration (Eta) were used to fit some water productivity functions for the different treatments. The results showed that both seeds yield and ETa parameters decreased with the increase in irrigation interval due to water deficiency and hence water productivity was affected. Application of K fertilizers minimized the influence of water stress on both parameters. The irrigation interval of 20 days and K fertilizer level of 300 kg ha^-1 seemed to be the most wisely selection for sesame crop under Sulaimaniya conditions. The percent of seeds yield decreased with the increase of irrigation interval and this percent of decrease was generally reduced with the increase of K application levels. For example using 20 days as irrigation interval (in comparison with 5-day interval) has saved nearly 70% of irrigation water while the reduction in yield was 16.2% for no K application and this was reduced to only 6.6% for the 300 kg K ha^-1 K level. In terms of the goodness of water productivity functions, the power function model proves superiority over the other models followed by parabolic model and then the exponential model. The weakest model was that of Stewart et al. (29), the linear model. This is because of the fact that the relationship between the yield and ET is not linear which what this model is.