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.
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ALVA et al. (1998) studied this question.