Effect of Controlled-release Nitrogen Fertilizers on Potato Yield and Nitrate Leaching in Northeast Florida.

Water availability and water quality in the Tri-county Agricultural Area (TCAA) in the lower St. Johns River basin are two critical concerns in northeast Florida. A three-year study was undertaken to evaluate the impact of an alternate seepage irrigation method and fertilization management on potato yield and water use efficiency. The field trial consisted of two levels of seepage irrigation systems (regular and reduced) in combination with two N sources- Urea and Controlled Release Fertilizer (CRF) at 168 and 224 kg N ha^-1. In 2006, a significant difference was observed in marketable yields, 27.6 MT ha^-1 and 22.5 MT ha^-1, under CRF224 and Urea224, respectively. No significant difference in yields was observed between CRF168 and Urea168. In 2007, marketable yield under CRF168 treatment (34.9 MT ha^-1) was significantly higher than Urea168 (29.4 MT ha^-1). Treatment CRF224 and CRF168 recorded the highest yields in 2006 and 2007, respectively. In 2006, the lowest mean NO₃-N concentration (0.51 mg L^-1) in the water table was observed under treatment CRF224. In 2007, treatment Urea224 recorded significantly higher mean NO₃-N concentration of 3.32 mg L^-1 in the water table than treatment Urea168 (1.85 mg L^-1). CRF treatments produced better yields in both years, and reduced nitrate leaching into the water table in 2006, compared to Urea treatments. No evidence, however, was found that CRF treatments helped reduce leaching compared to Urea treatments in 2007.