INTERACTION OF FERTILIZATION, ROOTSTOCK AND IRRIGATION ON GROWTH, THINNING EFFICIENCY, YIELD AND FRUIT QUALITY OF ´EMPIRE´ APPLE

A factorial field experiment comparing rootstock, fertilization and irrigation was established in 1992 at Geneva, New York, USA with 'Empire' apple trees. In 2003 and 2004, the interaction of the main effect factors and chemical thinning treatments was studied. Trees on M.9 rootstock grew 60% less over the two years than trees on M.7 rootstock. Trees on M.9 had significantly greater yield (19%), partitioning efficiency (151%), fruit color (9%) and farm gate crop value (19%), but had no effect on fruit size. Annual fertilization with ground applied NKB increased trunk cross sectional area increment of trees on M.7, but not of trees on M.9. Yield and crop value of both rootstocks was increased by annual fertilization. Fertilization had no effect on partitioning index. Fruit size of M.9 trees was increased by annual fertilization, but fruit size of M.7 trees was reduced by annual fertilization. Fruit red color of both rootstocks was reduced by annual ground fertilization. Annual ground applied NKB fertilizers increased leaf N, K, Mn and B but reduced P, and Ca. The addition of foliar nutrient sprays containing N, Mg, B, Cu and Zn did not increase tree growth, yield, fruit size or fruit color compared to annual ground fertilization only. Trickle irrigation caused a small, but significant increase in trunk cross-sectional area (5%), yield (5%), and crop value (6%), but reduced cumulative yield efficiency (7%). Chemical thinning of Benzyladenine+Carbaryl reduced fruit set and crop load more than with Naphtaleneacetic acid+Carbaryl. Trees on M.7 rootstock were much more responsive to both chemical thinners than trees on M.9 rootstock and were over thinned with both thinners. Annual ground fertilization of M.9 trees resulted in less thinning with NAA+Carbaryl than unfertilized trees. With the BA+Carbaryl treatment, there was no significant difference in thinning due to fertilization treatment on either rootstock.