Response of ‘Delicious’ Apple Trees in the Greenhouse to Rates and Forms of Nitrogen and Phosphorus in a Low phosphorus Soil

Abstract

Mono-ammonium phosphate applications to apple trees, ‘Oregon Spur’ seedling root (Malus domestica Borkh.), grown in a low P soil resulted in greater regrowth than the controls or other N or P soil treatments in the greenhouse. The high rate (12 g/tree) of mono-ammonium phosphate resulted in the most leaves per tree, the lowest percentage of leaves with purple margin, the highest level of leaf P and Mn, and relatively high levels of leaf N, K, Ca, and Mg. The 4 sources of N fertilizer (ammonium sulfate, ammonium nitrate, calcium nitrate, and urea) reduced the levels of leaf P in the trees. Trees treated with calcium nitrate had the highest level of leaf Ca.