FRUIT QUALITY IN RELATION TO FERTIGATION OF APPLE TREES

Abstract

The effect of fertigation on the mineral composition of apple fruits, their quality (colour, firmness, soluble solids) and storability was investigated from 1992 untill 1994 at the Research Station Bavendorf. In the first experiment with cultivars 'Elstar'/M9 and 'Boskoop'/M9 (2000 trees/ha) three fertigation treatments (two nitrogen levels and a calcium nitrate application) were compared to control (broadcast fertilization) and to irrigated trees (drip irrigation + broadcast fertilization). In the second experiment the influence of fertigation on quality parameters was investigated in relation to planting density (3330 and 6000 trees/ha with 'Jonica', 2000 trees/ha with 'Elstar'), crop density and fruit size at the cultivars 'Jonica'/M9 and 'Elstar'/M9. No significant differences were found in firmness, acidity, sugar content and their changes after storage between fruits from fertigated and non-fertigated plots. Fertigation did not improve the mineral content of the fruits in respect to their storability (Ca content, K/Ca-ratio). When the nitrogen level applied by fertigation was reduced this do not affect the skin colour. A calcium nitrate application did neither increase Ca in the fruits nor decrease the K/Ca-ratio. One reason for the homogenous fruit quality may be the applied size-selective thinning method. It was not possible to avoid alternate bearing by fertigation. No positive effect of fertigation on flowering and productivity of apple trees (annual and cumulative yields) was observed. Trees with drip irrigation and broadcast fertilization achieved the maximum yield of dessert fruits. A comparison of different factors showed that fruit quality was mostly affected by the number of fruits per tree. At low crop density firmness and content of soluble solids were higher and therefore the apples tasted better than at high fruit density. However storability decreased as a result of lowered Ca-levels in the fruit and higher K/Ca-ratios. Firmness and storability also decreased with increasing fruit size. These negative quality parameters both at low crop density and large fruit size could not be improved by fertigation.