Spatial and Temporal Distributions in Sandy Soils with Seepage Irrigation: II. Phosphorus and Potassium

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