Response of apple and pear trees to nitrogen, phosphorus, and potassium fertilizers

Apple (Malus domestica, Borkh) and pear (Pyrus communis, L.) trees responded to nitrogen (N), phosphorus (P), and potassium (K) fertilizers. In low P soils, leaf, and fruit P concentrations were increased and yield was improved with moderate rates of mono-ammonium phosphate (MAP) fertilizers. Improved fruit quality including fruit firmness, red fruit color of 'Delicious' apples, and a lower incidence of fruit disorders of apples (bitter pit) and pears (alfalfa greening and cork spot) was frequently associated with trees that were fertilized with calcium nitrate [Ca(NO3)(2)] (CN). Although yield was often improved in experiments containing N-P-K or MAP fertilizers, long-term use of N-P-K or MAP could be associated with a higher incidence of fruit disorders and a lower soil pH than with CN fertilizer at equivalent rates of N.