Potassium and Phosphorus

Abstract

In the Pacific Northwest, certain apple and pear orchards growing in low‐phosphorus soils lack tree vigor and produce low yields. In an attempt to correct this condition, treatments of mono‐ammonium phosphate (MAP) and nitrogen fertilizers (ammonium sulfate, ammonium nitrate, and calcium nitrate) were applied to 15‐year‐old ‘Golden Delicious’ and ‘Goldspur’ apple trees, (Malus domestica Borkh.) and observed over a 3‐year period. Test trees were growing in a soil containing a pH of 8.3 and 3 ppm available P. Concentrations of leaf and fruit P from MAP‐treated trees were higher by about 50 percent and 100 percent, respectively, than those of control or N‐only fertilized trees. Shoot extension and fruit size was greater in all fertilized trees than in unfertilized control trees. In some instances, fruit quality (finish, firmness, soluble solids, and control of scald and bitterpit) was improved on trees treated with MAP or Ca than with (NH₄)₂SO₄ or NH₄NO₃.

Key words:

• Malus domestica
• mineral nutrition
• mineral analysis of leaves and fruit