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.