M. El-Otmani, A. Ait-Oubahou, F. Zahra, C.J. Lovatt
Foliar fertilisation was reported be an efficient way to supply nitrogen to fruit trees and to reduce nitrogen losses to groundwater systems and risks of soil pollution and salinity. In this study we report on: 1) the effect of pH of a 1% urea solution applied prebloom and the effect of a multiple foliar-urea spray at the rate of 1% to supply 46 g N/tree to mature ‘Cadoux’ clementine mandarin trees (Citrus reticulate Blanco) on leaf N and its changes during 30 days following application; 2) the resulting effect on yield and fruit size; 3) a comparison made between effects of prebloom foliar application of urea at 0.8% or 1.6% (supplying 37 and 74 g N/tree, respectively) with prebloom soil applications of ammonium nitrate supplying 75 or 150 g N/tree on fruit size, fruit set and total yield. Results indicate that foliar urea increased leaf N content during the first 48 hours following treatment regardless of pH. Lowering the pH (from 7.6) significantly increased leaf N with the greatest increase occurring at pH=5.5-6.0. Urea effect on leaf N was nil by the 30th day after treatment. Fruit yield was significantly affected by urea applications. Cumulative yield was greatest at an improved pH value of 6.5. Yield improvement was due to increased fruit number since fruit size was not affected by the urea spray or its pH. The total number and weight of export grade fruit (diameter > 51 mm) was increased. The two foliar-urea rates and the soil-ammonium nitrate treatments had similar total and export yields both significantly greater than untreated trees. These results indicate that foliar-applied urea is an efficient, cost-effective way to supply N to clementine trees and that its efficiency is greater at pH 6.5.
El-Otmani, M., Ait-Oubahou, A., Zahra, F. and Lovatt, C.J. (2002). EFFICACY OF FOLIAR UREA AS AN N SOURCE IN SUBSTAINABLE CITRUS PRODUCTION SYSTEMS. Acta Hortic. 594, 611-617
DOI: 10.17660/ActaHortic.2002.594.82
leaf nitrogen, pH, ammonium nitrate, yield, fruit size, nitrogen source, clementine, Citrus reticulata, alternate-bearing

Acta Horticulturae