The characteristics of foliar potassium uptake in pistachio as affected by the fertilizer source and solution pH

Foliar spraying is one of the common methods to meet the nutritional needs of fruit trees, but the efficiency of this method largely depends on the characteristics of nutrient element uptake by the leaves. In this study, the characteristics of foliar potassium (K) uptake in pistachio (Pistachio vera L. cv. Owhadi) as affected by K fertilizer source and the solution pH was investigated in both intact and detached leaves. Potassium fertilizer solutions differing in pH (4.5, 5.5, 6.5, and 7.5) were provided by using K2SO4 and K-lysine and K-methionine amino acid complexes. Foliar sprays of K led to greater contribution of symplastic fraction to the apoplastic fraction; although this effect varied upon the K source and solution pH. The lowest distribution of apoplastic K was observed at the K-Met-treatment, while the leaves treated with K2SO4 retained the largest amount of K in the apoplastic spaces. The absorption of K by pistachio leaves from all K fertilizer sources declined as pH increased to 7.5. The decrease in the foliar uptake of K was significantly affected by the K source. At pH > 5.5, foliar uptake of K was greater from the K-Met-in comparison with K2SO4. This study suggests that foliar K uptake is affected by fertilizer source and solution pH. Higher symplastic distribution of foliar-applied K explains at least in part, higher nut K concentration in the pistachio trees treated with the K-amino acid complexes compared to those treated with K2SO4.

Automated summary

Foliar spraying is a common method to provide nutrient elements to fruit trees, but its efficiency depends on the characteristics of leaf uptake. This study investigated the foliar potassium uptake in pistachio trees with different fertilizer sources and solution pH. It was found that the effect of foliar K uptake varied with K source and solution pH. The study suggests that foliar K uptake is affected by fertilizer source and solution pH, and the distribution of K in the leaf cells explains the higher nut K concentration in trees treated with K-amino acid complexes compared to K2SO4.