SEASONAL ACCUMULATION OF MINERAL NUTRIENTS BY KIWIFRUIT I. LEAVES

The accumulation of macro and micronutrients by leaves of 30 mature kiwifruit vines (Actinidia deliciosa var. deliciosa Hayward) from two high-producing orchards was recorded over a growing season. An assessment was also made of the extent of which mobilization of nutrients stored in the vine from the previous season contributed to the nutrient status of the leaves during the early part of the growing season. The seasonal patterns for the concentrations of the various nutrients in the leaves could be broadly grouped into three types. Concentrations of potassium declined throughout the season, whereas nitrogen, phosphorus, copper and zinc concentrations declined initially but reached values which remained relatively constant by mid-season. For calcium, magnesium, sulphur, boron, manganese and iron, concentrations in the leaves also declined initially but then increased for the remainder of the season. There was no apparent seasonal pattern for sodium or molybdenum. A strong association was found between soil temperature and the concentration of potassium in the leaf. The period of greatest accumulation of nitrogen, potassium, phosphorus, sulphur, copper and zinc by the leaves occurred from leaf emergence to fruit set. Magnesium, calcium, boron, iron and manganese differed from the other nutrients in that the rate of accumulation was relatively constant throughout the season. Experiments with excised one-year-old extension canes indicated that the mobilization of macro and micronutrients stored in the plant from the previous season could have supported 20 to 40 % of the leaves on the vines during the first 30 d of growth. The developing fruit had a marked effect on the potassium and nitrogen status of the leaves, particularly those close to fruit. The substantial losses of potassium (21 to 37 %) and nitrogen (16 to 22 %) from the leaves after fruit set were sufficient to satisfy the requirements of at least 40 % of the fruit on the vine. The much smaller losses of the other nutrients from the leaves (less than 15 % of the total quantity present) reflected their lower mobility in the plant and the small demand by the developing fruit for these elements.