Vol. 69 No: 3

Title:
Yield Benefits Associated with Pre-Blossom Low-Biuret Urea Sprays on Citrus spp.

Author:
E. RABE

pp: 495-500

Abstract:
This 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 field variation no consistent trend with respect to the effect of the urea spray on changing the blossom composition (leafless vs. leafy inflorescences) could be demonstrated. Despite the increased ammonia levels recorded, no longer term increases in reserve leaf N levels were obtained.

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