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Abstract
Nitrogen (N) fertilization influences apple (Malus × domestica Borkh.) yield and quality, but less is known about the effect of rate and timing of fertilization on fruit quality. Rate and time of N fertilization (114 g/tree in Nov.+68 g/tree in May, 227 g/tree in Aug., 45 g/tree for 4 weeks starting in Aug., 136 g/tree in Aug., and 68 g/tree Aug. and May) affected N concentrations in flowers, bourse leaves, and in mid-terminal leaves of current season's growth. Return bloom and yield were highest for trees with the highest rate of N applied in August and they were lowest for trees with the lowest rate of N applied in a split application in May and August. Fruit size, color, firmness, soluble solids, and titratable acids, either at harvest or after 90 days in regular atmosphere storage, were not influenced by all five relatively low rates of N application. The best N treatment for fruit quality was with the low rate of N application in August. Highest fruit firmness, soluble solids content, and titratable acidity after storage occurred in fruit from trees that were harvested in 1997 with the lowest yield, regardless of N application. Return bloom, flower, and leaf N were good predictors of yield. Due to alternate bearing tendencies yield was a better predictor of fruit firmness, soluble solids, and titratable acidity than leaf N. The best N treatment for highest yield without sacrificing fruit quality was a single application (227 g) in August each year.
ACKNOWLEDGMENT
The authors express appreciation to the Washington State Tree Fruit Research Commission for grants funds partially supporting this study.