INFLUENCE OF FERTILIZER TREATMENT ON APPLE FRUIT COMPOSITION AND PHYSIOLOGY .2. INFLUENCE ON RESPIRATION RATE AND CONTENTS OF NITROGEN, PHOSPHORUS, AND TITRATABLE ACIDITY

The respiration rates and tissue contents of nitrogen, phosphorus, and titratable acidity were determined for apple fruit from trees receiving differential fertilizer treat ments U, N, P, NP, and NPK (U, no fertilizer; N, 2 lb ammonium sulphate; P, 4 lb superphosphate; and K, 1 lb potassium sulphate, per tree per year). The results obtained (expressed on a dry weight basis) are summarized as follows: Respiration rate: N> NP =NPK = U>P. Total nitrogen content: NPK>NP = N>U= P. Ethanol-insoluble nitrogen content: NPK = NP = N>U = P. Ethanol-soluble nitrogen content: NPK > NP = N > U = P. Phosphorus content: P > NP = NPK > U > N. Titratable acidity content: NPK>N>NP = U>P. The incidence of internal breakdown in stored fruit from these treatments was positively correlated with respiration rate per cell and negatively correlated with phosphorus content. Phosphorus content was negatively correlated with cell volume and respiration rate. Mechanisms by which phosphorus content might regulate the incidence of internal breakdown are discussed. © 1969 CSIRO. All rights reserved.