Sorption‐Desorption and Solution Concentration of Phosphorus in a Fertilized Sandy Soil

There has been increasing concern about drinking water contamination and accelerated eutrophication of surface water bodies. A field experiment was conducted to assess leaching potential of PO4‐P in a Riviera fine sand (loamy, siliceous, hyperthermic Arenic Glossaqualf) under grapefruit (Citrus paradisi Macfad.) production that received 0 to 30 kg P ha−1 yr−1. The PO4‐P concentration was measured in soil solution sampled using suction lysimeters installed above (120 cm) and below (180 cm) the hardpan (argillic horizon). Phosphorus sorption‐desorption in soil samples from different depths of the soil profile was determined to understand the transport and leaching of P in the sandy soil. Phosphorus sorption capacity of the argillic horizon was much greater than the soil above and below it. The PO4‐P concentrations in soil solution varied from 0.031 to 0.976 and from 0.002 to 0.083 mg P L−1 at the 120‐ and 180‐cm depths, respectively. Solution PO4‐P concentrations generally increased with P application rates. The concentrations of P in solution at the 120‐cm depth were much greater than those at the 180‐cm depths, due to the greater P retention capacity of and restricted flow of P through the hardpan. This study demonstrates that leaching of P into groundwater was reduced by the presence of a hardpan in the Riviera fine sand. However, the water drained from the soil above the hardpan contains phosphorus and could be a potential P source to surface waters.