SEASONAL PATTERN OF ACCUMULATION OF NUTRIENTS BY KIWIFRUIT 'HAYWARD' IN ACID SOILS OF NORTHERN PORTUGAL

Abstract

Kiwifruit production in Spain and Portugal is mainly developed on acid soils, where Ca supply to crops can be limited. Previous surveys in the same area concluded a widespread lack of Ca in leaves and kiwifruits; and, it is well established this nutrient is of utmost importance for fruit quality. The aim of this work is to record the changes in concentration, distribution and quantity of macronutrients in leaves and fruits and to report the effects of foliar fertilization in a high-producing orchard representative of acid soils. The experiment was conducted in Portugal on mature kiwifruit plants, weekly fertigated and alternatively supplied with foliar fertilization. Leaves and fruits analyzed for mineral concentration were sampled respectively four times and eight times from fruit set up to harvest, recording fresh and dry weight accumulation at the same time. Results showed that N and K accumulated by the fruit increased linearly through the entire growing season whereas the rate of Ca accumulation showed a sigmoid pattern, reaching its peak ten weeks after fruit set. There was a positive response to fertilization on leaf concentration of K, Ca, Mg and dry weight accumulation but a negative relationship with N concentration. This direct relationship was maintained for fruit N and K, whereas Ca and Mg was inversely related to foliar application. It seems that the more vigorous growth induced by additional fertilization reduced the Ca supply to fruit. The significance of the first weeks of fruit development on final Ca accumulation is also clearly stated.