Seasonal potassium dynamics in fruiting and non-fruiting branches of pistachio trees in relation to crop load

Abstract

Under dry and warm environmental conditions, the main Tunisian pistachio cultivar Mateur does not show a normal ‘On/Off’ cycle with highly variable nut yield, which could be affected by the tree nutritional status. In this context, Potassium (K) is considered a key nutritional element for nut development and for yield. The current study investigated the effects of alternate bearing and flower bud removal on seasonal dynamics of potassium in fruiting and non-fruiting branches of mature pistachio trees (cv. Mateur) in arid land. Three disbudding treatments were considered in reference to untreated trees taken as a control (T0): removal of all flower buds for one year (T1), or two successive years (T2) and removal of 50% of flower buds each year (T3). Similar K concentrations were detected early in the season in leaves, current shoot and one-year-old wood for all treatments. Current shoot begin the cycle with higher K concentrations, which declined during the lignification of endocarp and seed growth stages to finally accumulate K during postharvest. Inversely, one-year-old wood stored a large amount of K during the stage I and II of nut development, and became the main sink for K of the bearing shoot. Leaf K concentration explained 75% of yield variation. Yearly removal of 50% of flower buds induced less variation of leaf K concentrations (ranged between 0.5-0.8% DM) with regular nut yield compared to bi-annual On-Off cycle. Thus, under severe climatic conditions, the annual pruning could be applied to improve the nutritional status of pistachio trees.