Leaf analysis as a guide to the nutrition of fruit crops. X. Magnesium and phosphorus sand culture experiments with apple

Abstract

Abstract Sand culture pot experiments were carried out on young virus ‐ tested dessert apples, on MM.104 rootstocks, to study the effects of different levels of nutrient Mg and P on growth, flower production, crop yield and leaf nutrient composition. The relationship between leaf nutrient status and growth and fruiting was also investigated with a view to establishing “critical” leaf nutrient values for Mg and P. Variations in leaf Mg, over the range 0.07 to 0.33% Mg in dry matter (August sampling), had no significant effect (5% level) on growth and fruiting, although magnesium deficiency symptoms appeared on trees with leaf values less than 0.15% Mg in dry matter. Sub‐clinical concentrations of leaf P had very pronounced effects on growth, flowering and yield. Raising leaf P (July) from 0.15 to 0.25% P in dry matter doubled the number of flowers (in some years) in the following season and substantially increased growth and crop yield. In the absence of other limiting factors, and with adequate levels of N, the “critical” leaf P level in July—August would appear to be in the region of 0.25% P in dry matter.