Yield benefits associated with pre-blossom low-biuret urea sprays onCitrusspp.

Abstract

SummaryThis study evaluated the potential yield benefits of pre-blossom urea sprays on various Citrus spp. and to ascertain whether these yield benefits are as a result of altering the blossom composition or of supplying readily utilizable N during the critical flowering/fruit set period. Pre-blossom low-biuret urea sprays, 6–8 weeks before anthesis, at 1% concentration, one or two sprays 10–14 d apart, have resulted in significant (P<0.05) yield benefits in certain orchards. Experiments were conducted over a period of 2–4 years. Cultivars evaluated included ‘Shamouti’ oranges, ‘Ellendale’ tangor and ‘Minneola’ tangelo. In orchards where the leaf N level was below optimum the results were most significant while only slight or no yield responses were obtained in orchards where N levels approximated or exceeded 2.6%. Endogenous leaf ammonia levels were significantly increased for 14–30 d after the spray. This indicated a beneficial N level during the critical flowering and fruit set period. Because of large...