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ISHS Acta Horticulturae 627: XXVI International Horticultural Congress: Toward Ecologically Sound Fertilization Strategies for Field Vegetable Production

LONG-TERM EFFECT OF FERTILIZATION AND IRRIGATION RECOMMENDATIONS ON WATERMELON YIELD AND SOIL-WATER NITRATE LEVELS IN FLORIDA'S SANDY SOILS

Authors:   E. Simonne, M. Dukes, R. Hochmuth, G. Hochmuth, D. Studstill, W. Davis
Keywords:   Citrullus lanatus, Best Management Practices, BMP
Abstract:
The Surface Water Improvement Management (SWIM) Act of 1987 declared that several water bodies in Florida were at risk of becoming degraded from point and non-point sources of pollution (including agriculture, and vegetable production). With approximately 142,000 ha, the vegetable industry in Florida has an estimated value of $1.2 billion. Consequently state agencies, water management districts, and the University of Florida are developing and testing Best Management Practices (BMPs) aimed at reducing alleged non-point source pollution. The philosophy and purpose of BMPs is to produce economical yields of vegetables while minimizing the impact of production on ground water nitrate nitrogen (NO3-N) levels. Watermelons were grown in the spring between 1998 and 2002, following the recommendations of the Institute of Food and Agricultural Sciences (IFAS). Nitrate levels in the soil water at the 1.6-m and 7-m depths were monitored every three weeks with suction cup lysimeters and wells, respectively. Watermelon marketable yields ranged between 43,680 and 72,280 kg/ha, and were comparable to current commercial yields. Nitrate-N in the lysimeters ranged from 20 to 150 mg/L NO3-N except when rye cover crops were grown between vegetable crops. Under rye cover crops, NO3-N levels in the lysimeter samples ranged between 5 and 20 mg/L NO3-N. Those in the monitoring well samples were always below 20 mg/L NO3-N. It was concluded that economical yields of watermelon may be produced with current recommendations, and that under these growing conditions, NO3-N levels at the 1.6-m depth may range between 0 and 90 mg/L NO3-N. These results suggest that it is not possible to maintain NO3-N levels in the soil water or the shallow groundwater below the EPA drinking water standard, when current recommendations are followed. Reducing soluble fertilizer rates to reduce nitrate levels to or below 10 mg/L NO3-N is likely to reduce yield.

This research was supported by the Florida Agricultural Experiment Station and approved for publication as Journal Series No.N-02292

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