Effects of foliar fertilizers on abscission, fruit quality and tree growth in an integrated apple orchard.

In Switzerland, apple growers in some production areas tend to apply foliar fertilizers for improving yield and fruit quality. However, data supporting usefulness for sustainable production of high quality fruits are often lacking. Between 1992 and 1994, several foliar fertilizer treatments were compared in an apple (Malus domestica) orchard of cv. Jonagold on rootstock M9, planted in 1977. The orchard management was representative for the important apple production area Thurgau in North-Eastern Switzerland and followed the Swiss guidelines of Integrated Production. Mineral fertilizers had been applied based on nutrient requirement figures of apple trees and soil analyses. Foliar fertilizer treatments represented some most commonly used options: 'Algan' applied in spring (0.1%) and/or autumn (0.2%). 'Wuxal' (NPK plus microelements) applied in spring (0.2%), and urea (0.5%) applied in spring. with 6-9 applications per year and treatment. Furthermore, CaCl2 was applied in autumn on every second tree. Thinning procedures were according to common practices and included a hand thinning after June drop. No treatment effects on flowering and crop load were found. However, urea decreased abscission, fruit colour and sugar/acid ratio and increased fruit size and vegetative growth. Combined early and late applications of Algan tended to increase sugar/acid ratio and enhance the development of fruit colour. Taking into account agronomical. ecological and economical considerations, it was concluded however, that under the agroecological conditions of North-Eastern Switzerland no clear benefits arise from the application of the tested foliar fertilizer treatments in orchards that are managed and fertilized according to integrated production guidelines without evident physiological or nutritional disorders to be addressed.