Effect of Long-term Swine Effluent Application on Selected Soil Properties

Improving swine effluent management practices requires understanding of the fate of nutrients derived from swine effluent in soil quality. This study was conducted to evaluate the effects of long-term swine lagoon effluent application on nutrient distribution in an alkaline Okolona silty clay, an acidic Vaiden silty clay, and a Brooksville silty clay loam. Swine effluent has been applied using a center-pivot irrigation system at a total rate ranging from 10 to 15 cm ha of effluent per year since 1990. In October 2005, soil samples were taken from the irrigated and nonirrigated sites at the following depths: 0 to 5, 5 to 15, 15 to 30, 30 to 60, and 60 to 90 cm. Soils were air-dried, ground to pass 2-mm sieve, and analyzed for selected chemical properties. Sorption isotherms were also performed on the soil samples to determine P sorption capacity and strength. Long-term application of swine effluent resulted in a decrease in soil pH and an increase in soil electrical conductivity in all three soils. Total soil C and microbial biomass C increased in irrigated sites for all soils. Soil ammonium, nitrate, acid-extractable P, water-soluble P, and Zn concentrations were elevated at the 0to 5-cm and 5to 15-cm depths, and their values were extremely lower in the alkaline Okolona soil than in the Brooksville and Vaiden soils. No clear effect was observed for P sorption strength and capacity. Low N and P accumulation in alkaline Okolona soil may prolong the capacity of this soil in receiving swine effluent particularly if threshold water-soluble P and soil test P levels are used as part of swine effluent management program. (Soil Science 2008;173:223-235)