Potassium fertilization affects soil K, leaf K concentration, and nut yield and quality of mature pistachio trees

A field experiment was conducted from 1996 to 1998 to examine the effects o f K fertilization on leaf K, nut yield, and quality in pistachio (Pistacia vera L.). There were six treatments, including four annual rates of K appli cation (0, 110, 220, and 330 kg.ha(-1)) and three K sources (K2SO4, KCl, an d KNO3), Pistachio trees exhibited highly fluctuating seasonal leaf K level s, Leaf K concentration was low (<10 g.kg(-1)) during spring flush, increas ed dramatically during fruit development, and declined rapidly after harves t, Leaf K concentration increased following K fertilization. Potassium fert ilization at the rate of 110 to 220 kg.ha(-1) K significantly increased nut yield and quality, but nut yield tended to decrease when the annual rate e xceeded 220 kg.ha(-1) K, There were no significant differences among the K sources in their effects on leaf K concentration, nut yield, and quality. T he use of KCl as a K source for 3 years did not increase leaf Cl concentrat ion. There was a significant, positive correlation between nut yield and le af K concentration during nut fill. The critical leaf K value for optimal p istachio production determined from 3 years' cumulative data was 16.9 g.kg( -1). For sustained production in highly productive pistachio orchards, we r ecommend annual application rates of 110 to 220 kg.ha(-1) K, using K2SO4, K Cl, or KNO3.