Critical stage of nitrogen requirement for citrus fruit development

Abstract

Nitrogen (N) requirement for citrus (Citrus sinensis) fruit growth and development was studied from June to December for Parson Brown, Hamlin, Valencia, and Sunburst orange varieties which received either 168, 224, or 280 kg N ha^-1 yr^-1. Fruit yield was not significantly influenced by the above N rates over the three years of study. Fruit diameter increased appreciably from June to September (32 to 57 mm for Sunburst, 44 to 70 mm for Parson Brown and Valencia, and 48 to 70 mm for Hamlin), followed by a slow increase until December. Fruit dry weight almost doubled from June to September and continued to increase slowly during the latter half of the growing period. Nitrogen content in the fruit increased from 107 to 217, 113 to 258, 131 to 315, and 134 to 269 mg per fruit between June to September for Hamlin, Sunburst, Valencia, and Parson Brown varieties, respectively. From the N management point of view, adequate availability of N is critical during early fruit development. On the basis of fruit weight and N in fruit, fruit production of 1235 boxes (Box = 40.8 kg) per hectare accounts for 66, 71, 73, and 81 kg N in the fruits, respectively, for Hamlin, Parson Brown, Sunburst, and Valencia orange varieties. This study demonstrates significant genotypic differences with respect to N requirement for fruit development.