Cover crop and mulching effects on yield and fruit quality in unsprayed organic apple production

Abstract

Summary To determine the optimal growing system for organic apple production three different cover crop management practises were established for two scab resistant apple cultivars; cultivar A 'Prima' and cultivar B 'Vanda'. The management practices included: Treatment 1: A permanent grass mixture in the alley way, Treatment 2: A permanent clover grass mixture in the alley way and Treatment 3: An annual mixture of grass and clover was sown every year in early July and mulched down the following year in April. Mechanical weed control in the tree rows was carried out yearly from April to July. No additional fertilizer, irrigation or pest and disease control were carried out. A mulching sub trial was conducted in the cover crops: after mowing the cover crops in Treatment 1 and 2: clippings were mulched into the tree row (Treatment A) or clippings were left in the alley way (Treatment B). The permanent grass alley way system (Treatment 1) resulted in the lowest shoot growth, the lowest level of nitrogen in leaf dry matter and fruit with the highest percentage of skin colour. The permanent clover grass mixture (Treatment 2) increased the nitrogen level in the leaves and decreased the percentage of skin colour, moreover the apple scab and fly speck infection on the fruit skin increased compared to fruits produced in Treatment 1. The annual cover crop growing system (Treatment 1) produced vigorous tree growth, a high level of nitrogen in the leaves, high soil water content in the alley way, the highest yield of large fruits and a low percentage of skin colour. The mulching trial showed that leaving clippings of grass in the alley way (Treatment B) resulted in a lower yield of coloured fruit compared with fruit harvested following mulching of the clippings into the tree row (Treatment B). This effect was not only obtained for grass (Treatment 1) but also for clover grass clippings (Treatment 2). The soil water content in the tree row was highest following mulching clover grass. For the permanent grass system the highest content of soil water in the tree row was obtained for bare soil.