Phosphorus in zero tension soil solution as influenced by long-term fertilization of corn (Zea mays L.)

Abstract

Phosphorus from fertilized agricultural land may contribute to ground or surface water inputs and accelerate eutrophication. With increases in soil P saturation and organic P in long-term fertilized soils, soil P leaching losses may increase. The effect of long-term P fertilization (6 to 11 yr) on inorganic and organic 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 inorganic 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 increased 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 in the Chicot soil and from 312 to 974 g ha−1 yr−1 in the Ste. Rosalie 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 required 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 considered in association with soil type to predict potential water contamination. Key words: Continuous corn, long-term fertilization, soil solution, dissolved inorganic and organic P, NaHCO3 extractable P