Regrowth Performance of Apple Nursery Plants in Relation to Reserve and Current Uptake of Nitrogen

Abstract

Gala/M26 apple plants previously treated with foliar urea (0%, 2%, and 4%) were fertigated with or without 15N-depleted ammonium nitrate by using a modified Hoagland solution after transplanting in the spring. Plants with high N reserves had significantly greater growth than plants with low N reserves. More nitrogen was remobilized for new shoot and leaf growth in plants with high N reserves than plants with low N reserves. The amount of reserve N used for new shoot and leaf growth was not affected by current supply of nitrogen. There was no significant difference in the amount of nitrogen from current uptake used for new shoot and leaf growth between low and high N reserve plants up to 80 days after spring budbreak. The amount of N from current uptake for new shoot and leaf growth was negligible at 20 days after budbreak. Plants with low N reserves were more dependent on current uptake for sustaining new shoot and leaf growth and maintaining their nitrogen status than plants with high N reserves. After 80 days of growth, plants with low N reserves did not catch up with the plants with high N reserves.