Effects of autumn foliar application of15n‐urea on nitrogen storage and reuse in apple1

Effects of autumn foliar application of N‐urea on N storage and reuse in young apple seedling (Malus Pumila Mill.) were studied. Foliar application of urea‐15 N (3.5%) during autumn enhanced the retranslocation of leaf N to other plant parts and increased stored N. Foliar N sprays increased the proteolytic activities of the leaves; therefore, such activities appear to be a major mechanism of retranslocation of leaf N. Foliar applied N enabled the plant to produce more growth during the following seasons. A considerable portion of the plant total N during second and third years was attributable to the foliarly applied N during the first year.