Nutrient Balance and Use Efficiency in Sandy Soils Cropped with Tomato under Seepage Irrigation

Decreasing groundwater and surface water quality relative to land use, poorly retentive sandy soils, frequent and intensive rainfalls, and shallow groundwater depths is a major concern in Florida. While the spatial and temporal distributions of N, P, and K in southwest Florida sandy soils cropped with seepage-irrigated tomato (Solanum lycopersicum L.) were previously described, the objective of this study was to calculate seasonal nutrient balances and estimate potential nutrient losses for field conditions. Field experiments were conducted in 2006 spring and 2006/2007 winter growing seasons with 224 or 358, 61, and 553 kg ha(-1) of N, P, and K fertilizer, respectively. Total inorganic soil N in the root zone decreased with time, reaching minimum concentrations at the end of growing seasons. Total Mehlich-1 soil P fluctuated widely in the spring but remained relatively constant in the winter season, yet was slightly higher than the preplant values for both seasons. Total Mehlich-1 soil K decreased with time, but large concentrations remained in the soil at the end of both seasons. Potential nutrient loss from the root zone ranged from 35 to 38, 41 to 43, 0 to 2, and 15 to 37% for low N, high N, P, and K, respectively, for both seasons. Phosphorus probably underwent transformation from nonextractable to Mehlich-1 extractable forms during the season. Nutrient use efficiency ranged from 59 to 62, 52 to 55, 10 to 14, and 40 to 52% for low N, high N, P, and K, respectively, for both seasons. Leaching loss during the season was likely for N and K, and there is a post-harvest leaching risk for P and K on removal of the plastic mulch.