The effect of orchard factors on the chemical composition of apples. V. Year-to-year variations in the effects of NPK fertilizers and sward treatment on fruit composition

SummaryNitrogen, P, K, Mg, Ca, Na, titratable acidity and dry weight were measured in 11 successive crops of Cox’s Orange Pippin apple fruit from an N,P,K fertilizer and grass/cultivation orchard management trial. Yearly fluctuations in the concentrations of the constituents were often larger than differences due to experimental treatments. Concentrations of Na were especially variable from year to year and those of Mg followed a biennial pattern. There were also large variations in responses to treatments in different years: in some instances treatment effects were reversed. The varying responses of different constituents to treatments resulted in alterations in the relationships of K to Mg or titratable acid concentrations and Ca concentrations to mean fruit weight in some years. No simple interpretation of these fluctuations was possible in terms of meteorological data.