Abstract
In the period 1995-1999 sampling of apple leaves was performed in order to identify reference curves for a number of plant nutrients for the whole vegetative period, from bloom until after harvest. Approximately 2500 samples of apple leaves were analysed for N, P, K, Ca, Mg, B, Mn, Cu and Zn. The reference curves were derived for each element by adjusting the obtained curves to known reference values for the period of July and August. This system of leaf analysis has been found useful by growers in South Tyrol. INTRODUCTION Leaf analysis is a valuable method of assessing the nutritional status of plants. It allows optimisation of fertiliser applications with the aim of obtaining high yields of good quality fruit. Until recently, leaf analysis was usually performed relatively late in the season, namely during July and August. The results were interpreted using reference values for this precise period taken from literature (Bergmann and Neubert, 1976; Quast, 1983; Quast, 1986; Failla et al, 1991) and adapted to the local conditions in South Tyrol (Table 1). However, the most important period in terms of nutrient uptake is likely after bloom, when fruit trees have their highest nutrient demand. A better knowledge of the pattern of leaf nutrient concentration early in the season could also permit more timely applications of corrective measures. As the nutrient concentration of leaves varies during the season, any interpretation needs generally to be adjusted to the corresponding vegetative stage. It is hypothesised that if the seasonal pattern of the optimal concentration range for the individual elements and the fertiliser response of the plants during the growing season are known, fertiliser recommendations could be derived at any point in the season.