Effects of nitrogen rates on dry matter and nitrogen accumulation in citrus fruits and fruit yield

Fruit growth patterns and nitrogen (N) accumulation in fruit over the growt h period were studied on 'Valencia', 'Parson Brown','Hamlin', and 'Sunburst ' cultivars which received either 168, 224, or 280 kg N ha(-1) yr(-1) as br oadcast applications of N:P:K dry soluble granular fertilizer. Over a 4-yea r period, fruit yields of all cultivars did not respond to N rates during l ow production years. The effects of fertilizer rates were non-significant o n either fruit diameter, dry weight, or fruit N content. Fruit weight and f ruit diameter increased rapidly from June to Aug. or Sept., followed by a s low increase during the remainder of the fruit development period. Fruit si ze of 'Sunburst' was significantly smaller than that of the other three cul tivars, which showed no differences in fruit diameter or dry weight. Nitrog en accumulation in the fruit increased rapidly between June and Aug., follo wed by marginal or no increase during the remainder of the growth period. T hus, most of the N accumulation occurred prior to Aug., for all cultivars. Nitrogen content of mature fruit (fresh weight basis) followed the order: ' Valencia' > 'Parson Brown' ='Hamlin' > 'Sunburst'. Total N content of the f ruit at a given fruit yield level followed the order: 'Sunburst' = 'Valenci a' > 'Parson Brown' > 'Hamlin'. This study has clearly demonstrated that ad equate availability of N is critical during the initial fruit development a nd growth stages. Application of N later during the growing period will hav e minimal impact on the fruit yield. However, it could contribute to N rese rve in the tree, which may be utilized for fruit production the following y ear.