Irrigation and Nitrogen Management Effects on Potato Production and Nitrate Leaching in Northeast Florida.

A three-year study was undertaken to evaluate the impact of irrigation and fertilization management on potato yields and water use efficiency in the lower St. Johns River basin in northeast Florida. The field trial consisted of three irrigation systems (regular and reduced seepage, and drip irrigation). Combination of two N sources - urea and a Controlled Release Fertilizer (CRF) - and two N rates (168 and 224 kg ha^-1) were used in the two seepage irrigation systems. Five N rates (0, 112, 168, 224, and 280 kg ha^-1) were used in drip irrigation system. In 2006, marketable yields of 28.5 MT ha^-1 and 22.1 MT ha^-1 under regular and reduced seepage irrigation, respectively, were recorded and the difference was significant. Yield levels were however similar in 2007 between the two seepage treatments. The mean NO₃-N concentration in the water table was lowest (0.51 mg L^-1) under treatment CR224 compared to other N treatments under seepage irrigation systems in 2006. Significantly higher mean NO₃-N concentration of 3.32 mg L^-1 in the water table was recorded under treatment urea224 in 2007, compared to treatment urea168. The interaction of irrigation and N management also affected nitrate concentrations in the water table. At 168 and 224 kg ha^-1 N rates, mean NO₃-N concentrations of 4.24 mg L^-1 and 8.32 mg L^-1 in the water table under drip irrigation, respectively, were significantly higher than concentrations of 2.1 mg L^-1 and 2.2 mg L^-1 under CRF treatments in seepage irrigation in 2007. Compared to drip irrigation management, seepage irrigation was more efficient to reduce nitrate concentration in the water table in 2007, but not in 2006.