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Impact of Nitrogen Management Practices on Nutritional Status and Yield of Valencia Orange Trees and Groundwater Nitrate

Univ. of Florida, Inst. of Food and Agricultural Sciences, Citrus Research and Education Center, 700 Experiment Station Rd., Lake Alfred, FL 33850;

W.D. Graham

Dep. of Agricultural and Biological Engineering, Univ. of Florida, Inst. of Food and Agricultural Sciences, Gainesville, FL 32611-0570.

^* Corresponding author (aka{at}gnv.ifas.ufl.edu).

ABSTRACT

A field experiment was conducted using 36-yr-old Valencia orange trees (Citrus sinensis) planted in an Astatula fine sand (hyperthermic, uncoated, Typic Quartzipsamments) to evaluate the effects of two different N management practices on the mineral nutrition status of the trees, fruit yield and quality, and nitrate (NO^–₃) loading into groundwater. The N treatments included 180 kg ha^–1 yr^–1 as either (i) three broadcast applications per year of a combination of dry soluble form (DSF; 135 kg N ha^–1 yr^–1) and controlled-release form (CRF; 45 kg ha^–1 yr^–1); or (ii) fertigation in 18 equally divided applications per year. Nitrate-N was measured in groundwater sampled at 3-wk intervals using four monitoring wells in each of the two blocks over 2 yr. Fruit yield was greater by 2.7 to 8.2 Mg ha^–1 in the fertigation compared to that in the DSF/CRF broadcast treatment. Leaf nutrient concentrations or fruit quality parameters were not significantly influenced by the different N management treatments. Most of the leaf nutrients were within the recommended optimal ranges. Mean groundwater NO₃-N concentrations for the DSF/CRF treatment ranged from 6.5 to 16.5, and 9.4 to 14.1 mg L^–1 during 1995 and 1996, respectively. The corresponding values for the fertigation treatment ranged from 7.0 to 14.6 and 1.4 to 6.9 mg L^–1. Fertigation with 18 applications per year decreased NO₃-N loading into groundwater as compared to three broadcast applications of the same rate of N using DSF/CRF granular blend.

Florida Agric. Exp. Stn. Journal Series no. R-6072.

Received for publication June 17, 1997.

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