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Title: EFFECTS OF NITROGEN RATES ON DRY MATTER AND NITROGEN ACCUMULATION IN CITRUSFRUITS AND FRUIT YIELD

Author
item Alva, Ashok
item PARAMASIVAM, S - UNIV OF FLORIDA
item HOSTLER, K - UNIV OF FLORIDA
item EASTERWOOD, G - HYDRO-AGRI NORTH AMERICA
item SOUTHWELL, J - HYDRO-AGRI NORTH AMERICA

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2000
Publication Date: 4/1/2001
Citation: ALVA, A.K., PARAMASIVAM, S., HOSTLER, K.H., EASTERWOOD, G.W., SOUTHWELL, J.E. EFFECTS OF NITROGEN RATES ON DRY MATTER AND NITROGEN ACCUMULATION IN CITRUSFRUITS AND FRUIT YIELD. JOURNAL OF PLANT NUTRITION, 24:561-572. 2001.

Interpretive Summary: The pattern of nitrogen translocation to citrus fruits and accumulation of nitrogen and dry matter are important to fine tune nitrogen management recommendations aimed to improve nutrient uptake efficiency. A field experiment was conducted using 'Valencia', 'Parson Brown', 'Hamlin', and 'Sunburst' cultivars which received either 168, 224, or 280 kg N/ha/yr. Rapid increase in fruit weight or diameter, as well as an increase of nitrogen accumulation, occurred during June to August or September. Total nitrogen content in the fruits is an important component of the overall nitrogen budget. For an estimated target fruit yield of 60 tons/ha, the total nitrogen content in the fruit represented 70, 75, 89, and 90 kg for the 'Hamlin', 'Parson Brown', 'Valencia', and 'Sunburst' cultivars, respectively. This study demonstrated that adequate availability of nitrogen is critical during the early growth period of the fruits.

Technical Abstract: Fruit growth patterns and nitrogen (N) accumulation in fruit over the growth 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 broadcast applications of N:P:K dry soluble granular fertilizer. Over a 4-year period, fruit yields of all cultivars did not respond to N rates during low production years. The effects of fertilizer rates were non- significant on either fruit diameter, dry weight, or fruit N content. Fruit weight and fruit diameter increased rapidly from June to Aug. or Sept., followed by a slow increase during the remainder of the fruit development period. Fruit size of 'Sunburst' was significantly smaller than that of the other three cultivars, which showed no differences in fruit diameter or dry weight. Nitrogen accumulation in the fruit increased rapidly between June and Aug., followed by marginal or no increase during the remainder of the growth period. Thus, 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 fruit at a given fruit yield level followed the order: 'Sunburst' = 'Valencia' > 'Parson Brown' > 'Hamlin'. This study has clearly demonstrated that adequate availability of N is critical during the initial fruit development and growth stages. Application of N later during the growing period will have minimal impact on the fruit yield. However, it could contribute to N reserve in the tree, which may be utilized for fruit production the following year.