The Effect of Understorey Management on Soil Fertility, Tree Nutrition, Fruit Production and Apple Fruit Quality

Abstract

Changes in understorey management which accompany a shift to organic production potentially affect water and nutrient relationships for apple trees. Here we report field trials from a biological production orchard established at Winchmore, Canterbury, New Zealand in 1989 which involved a study of the changes in nutrient status of soil and of apple trees within red clover, ryegrass and mixed herb ley understories. These changes were assessed by soil, leaf and fruit analysis and related to differences in fruit production, tree growth and fruit quality. Soil and leaf nutrient levels increased with additions of nitrogen and potassium in composts and mulches. Nitrogen levels changed with both herbage (main treatment) and mow management (sub treatment) and were higher in trees grown with legumes in the understorey than in trees grown with a ryegrass understorey. With apple varieties such as ‘Braeburn’ which are sensitive to calcium disorders, fruit calcium levels changed with understorey management, but the incidence of disorders was not affected. Fruit maturity was delayed by leguminous compared to non-leguminous understories and nitrogen levels in the fruit increased with the inclusion of the legume. The incidence of storage disorders was low in fruit from all biological production systems. Treatments to which nitrogen was applied as compost or as a legume component of the understorey had fruit with lower soluble solids and firmness than treatments grown with a grassed understorey. Changes in fruit quality and fruit maturity highlighted the importance of mulches and leguminous understories as contributors to the nitrogen and potassium nutrition of the tree.