The effect of potassium and nitrogen fertilizers on the yield, fruit quality and leaf analysis of Imperial mandarins

Abstract

A potassium and nitrogen nutrition trial with Imperial mandarins was conducted for four years at Gayndah in south-eastern Queensland with the following results. Annual applications of 0.5 or 2.0 kg potassium/tree increased average yields by 12.3 and 22.2%, respectively, over those of the nil control, which yielded an average of 163 kg fruit/tree.year. Fruit diameter and rind thickness were also increased and fruit colour development was hastened by the applied potassium. Average leaf levels of potassium resulting from the 0,0.5 and 2.0 kg treatments were 0.85, 0.93, and 1.35% in non-fruiting terminals and 0.40, 0.44 and 0.77% in fruiting terminals. The potassium levels in non-fruiting terminals fluctuated from year to year in an inverse pattern to the alternate yield pattern whereas the levels in fruiting terminals remained stable. With an annual application of 0.4 kg nitrogen/tree average leaf nitrogen levels were 2.83% in non-fruiting terminals and 2.32% in fruiting terminals. At 0.7 kg nitrogen/tree both these figures were increased by 0.11% but there was no effect on yield or fruit quality. When the nitrogen was applied in two dressings in winter, yield was 9% greater than when the same quantity was applied in spring-summer.