The Utilization of Post-harvest Urea Sprays by Senescing Apple Leaves1

Senescing apple leaves absorbed 80% of applied urea in 48 hr with greater absorption in light than in darkness. The amount of urea absorbed paralleled the increase in the concn of soluble N and urea N. The bulk of the increase in soluble N was urea and the changes in total soluble N paralleled the changes in urea N. During leaf senescence, chlorophyll, total N and protein declined and much of this N was translocated into storage tissues. Trees which received a post-harvest urea spray produced a significantly greater amount of shoot growth and fruit set of apples than trees receiving no urea or a soil application of urea. The yield was not significantly different between trees receiving a 5% urea spray and trees receiving the soil application of urea. However, the efficiency of N utilization by a 5% urea spray was 4-fold greater than the soil application.