PHOSPHORUS IN ZERO TENSION SOIL SOLUTION AS INFLUENCED BY LONG-TERM FERTILIZATION OF CORN (ZEA-MAYS L.)

Zhang, T. Q. and MacKenzie, A. F. 1997. Phosphorus in zero tension soi l solution as influenced by long-term fertilization of corn (Zea mays L.). Can. J. Soil Sci. 77: 685-691. Phosphorus from fertilized agricul tural land may contribute to ground or surface water inputs and accele rate eutrophication. With increases in soil P saturation and organic P in long-term fertilized soils, soil P leaching losses may increase. T he effect of long-term P fertilization (6 to 11 yr) on inorganic and o rganic P in soil solutions at zero tension was studied on two soils, a Chicot sandy clay loam (Grey Brown Luvisol) and a Ste. Rosalie clay ( Humic Gleysol). Soil solution samples were collected using a cylinder technique and analyzed for total dissolved P (TDP), dissolved inorgani c P (DIP), and dissolved organic P (DOP). Levels for DIP ranged from 0 .15 to 1.01 mg P L-1 and TDP ranged from 0.33 to 1.19 mg P L-1 in the Chicot soil. In the Ste. Rosalie soil, values of DIP ranged from 0.04 to 0.23 mg P L-1 and TDP ranged from 0.15 to 0.36 mg P L-1. Increasing fertilizer P applications from 44 kg ha(-1) to 132 kg ha(-1) increase d DIP and TDP in soil solutions in both soils. There was no effect of P fertilization rate on DOP values. Soil P movement below 45 cm during the non-growing season was estimated at 633 to 2732 g ha(-1) yr(-1) i n the Chicot soil and from 312 to 974 g ha(-1) yr(-1) in the Ste. Rosa lie soil. Soil solution DIP was found to be linearly related to soil P extractable with 0.5 M NaHCO3 but levels of NaHCO3-extractable P requ ired to produce 0.05 mg P L-1 DIP varied with soil, ranging from 70 to 110 mg P kg(-1) soil. The critical level of extractable P has to be c onsidered in association with soil type to predict potential water con tamination.