EFFECT OF IRRIGATION TREATMENTS AND TIME OF FOLIAR-APPLIED UREA ON YIELD OF NAVEL ORANGE (CITRUS SINENSIS L. OSBECK)

Abstract

This study investigated the effect of irrigation treatments and time of foliar applications of low-biuret urea on yield of 30-yr-old navel orange trees grown under optimal N fertilization. The experiment was carried out at the Agricultural Experiment Station of the University of California, Riverside, using split plot design with 12 replications. The two irrigation treatments were the mainplots and the urea applications were the subplots. Irrigation was withheld from one set of trees from October to March, the other set was irrigated according to commercial practice. Foliar-urea (0.17 kg/tree) was applied in November, December, January, or February.The results of the first year showed no significant differences between irrigation treatments with regard to total fruit weight or total number of fruit per tree, All trees receiving urea had significantly higher fruit weight and fruit number per tree than the control trees. The specific time of urea application had no significant effect.With respect to fruit size distribution, the irrigated treatment resulted in a significantly higher number of fruit of size 7.0-8.0 cm (box sizes 88-72). Generally, the non-irrigatd trees had more fruit of size 6.0 cm or less. No interaction between irrigation treatments and foliar urea sprays was observed.