The effect of timing of post-harvest foliar urea sprays on nitrogen absorption and partitioning in peach and nectarine trees

Summary

The effects of timing of autumn foliar urea-N sprays on nitrogen absorption and partitioning were studied in mature peach and nectarine trees. A 10% ¹⁵N enriched urea solution was applied by either dipping individual shoots in 1995 or spraying whole tree canopies in 1996. Trees whose canopies were sprayed during the post-harvest period with a 10% w:v urea solution in 1996 were excavated in the dormant season, and ¹⁵N contents and distribution were determined. Peach leaves rapidly absorbed urea-N irrespective of application date, and transport of urea-N to perennial tree parts occurred primarily within 4–7 d after application. Between 48 and 58% of the urea-N applied was recovered in abscinded leaves and perennial organs. Leaves exported ≥60% of the foliar-applied urea-N following application in early autumn (September or October), but <50% export occurred when applied shortly before leaf fall (November). Of the urea-N translocated, most was recovered in roots (≥38%) following application in September or October. Urea-N applied in November, however, remained largely in the current year wood (ca. 45%). Thus, export and translocation of foliar applied urea-N diminished during the final stages of leaf senescence. Foliar application of urea in September or October supplied the equivalent of about 20% of crop nitrogen content, but only 14% (i.e. ca. 30% lower) when applied shortly before leaf senescence in November.