Spatial and Temporal Distribution of Phosphorus (P) and Potassium and P Forms in Sandy Soils Cropped with Tomatoes under Seepage Irrigation.

Fertilizer management, particularly of phosphorus (P) and potassium (K), on sandy soils is crucial to maximized production and minimized environmental impact in agricultural systems. Experiments were conducted in commercial tomato (Lycopersicon esculentum Mill.) farms in southwest Florida for 2006-spring and -winter growing seasons to elucidate P and K distributions in tomato bed and determine leaching potential under seepage irrigation. Most of P was found in the top (0–10 cm) and middle (10–20 cm) soil layers of centerline (plant row) of the bed, and remained relatively constant. Phosphorus in the bottom layer (20–30 cm) and bed shoulder was similar or below pre-planting levels, which implied that P did not likely move outside the root zone. However, results from P fractionation and soil P storage capacity on the top-centerline sample revealed higher risk of P losses when applied P remained more in soil solution. Seepage irrigation may have limited downward water movement in the bed, thus P leaching, therefore P losses through surface runoff in-between growing seasons could be substantial. Most of K remained in the top layer of the fertilizer band in an order-of-magnitude higher concentration compared to the rest of the bed location, where low and constant amounts of K were found throughout the season. This indicated that there was little or no K leaching observed in this study. Current Best Management Practices for tomato fertilization should be monitored and evaluated.