Foliar urea pretreatment tempers inefficient N recovery resulting from copper chelate (CuEDTA) defoliation of apple nursery plants
2001
Guak, S. | Cheng, L. | Fuchigami, L.H.
Copper chelate (CuEDTA) defoliation of deciduous fruit nursery plants, although effective in leaf removal, causes inefficient N recovery from leaves, which results in reduced reserve N levels in woody perennial tissues, compared with natural defoliation. To correct this problem, we sprayed spring bench-grafted Fuji/M.26 apple (Malus domestica Borkh.) nursery plants with 3% urea twice, at 5 d intervals, 13.d prior to 1% CuEDTA spray treatment on 31 October, 1997. The effects of urea and CuEDTA on defoliation, reserve N, and later regrowth were determined, as compared with those of hand- or natural-defoliation. CuEDTA resulted in >80% defoliation within 6 d of application. The abscission induced by the CuEDTA treatment, however, did cause significantly less N to be withdrawn from leaves compared with those plants undergoing natural defoliation. This inefficient N recovery was tempered by the foliar-urea pretreatment. The application of urea substantially increased the reserve-N level (total-N or soluble-protein concentrations) in all components of the tree without affecting the efficacy of CuEDTA on defoliation. The extent of regrowth in N-deficient medium was proportional to the reserve-N level. The urea-treated plants, whether hand- or CuEDTA-defoliated, showed better growth performance than the no-urea controls. Therefore, CuEDTA, in combination with pretreatments of foliar urea, proved effective for defoliating apple nursery plants, increasing reserve-N levels, and improving regrowth performance during tree establishment.
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