Response of foster grapefruit (Citrus paradisi Macf.) to organic and inorganic fertilization in central Sudan

The response of Foster grapefruit (Citrus paradisi Macf.) to organic and inorganic fertilization in Sennar area (13°37′N–33°37′E) representing central Sudan, was studied for two successive seasons (2003/2004 and 2004/2005). Urea, sheep manure and terra-sorb (as foliar) at the rates of 2.17 kg/tree/year, 20 kg/tree/year and 200 ml/100 L water, respectively, and their combinations were applied to 18 years old trees to determine their effects on fruit yield and quality. The layout was a randomized complete block design replicated three times. Results indicated that all treatments significantly increased average yield over control with inconsistent effects on fruit quality parameters. Trees received urea at the rate of 2.17 kg/tree/year, yielded thick peel fruits of reduced vitamin C. Sheep manure at the rate of 20 kg/tree/year resulted in dark green fruits of thick peel. The foliar treated trees at the rate of 200 ml/100 L water gave little thick peel fruits of lower total soluble solids, low % titrable acidity and low vitamin C. The best fruits reflected by color, thinner peel, high % TSS and high vitamin C were obtained from urea + sheep manure treatment. Application of urea with foliar gave green large fruits. Small fruits of intensive green color on surface and low titrable acidity were recorded by combination of sheep manure and foliar. Application of the three fertilizers together gave fruits of dark green color on surface and thick peel. Therefore, application of 2.17 kg urea + 20 kg sheep manure/tree/year is recommended to Foster grapefruit trees in Sennar area and areas of similar environmental conditions