Soil and waste management effects on phosphorus leaching in acid sandy soils of the North Carolina coastal plain

Excess phosphorus applied to soils with low P adsorption capacities can potentially enter surface water via leaching and subsurface transport, thereby negatively impacting surface water quality. Currently proposed best management practices for inhibition of P leaching are limited to reducing the P application rates, which can decrease the economic viability of animal producers. The protection of water quality and sustainability of animal production are dependent on accurate descriptions of waste and soil management effects on P leaching. Development of new best management practices will benefit both the environment and animal producers. This requires further data and research to adequately describe the risk of P loss via leaching and determine the effects of new best management practices on P leaching. The objectives of this research are to: (1) monitor P concentrations in the soil solution of soils with long-term histories of swine lagoon effluent application and relate these P concentrations to easily quantifiable soil properties, (2) modify the GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) model P subroutines to more accurately reflect P sorption/desorption and validate the modified model with collected field data, (3) use the validated version of GLEAMS to determine cropping system and waste management effects on long-term P leaching losses, and (4) evaluate the use of alum (Al₂(SO ₄)₃·14H₂O) additions to soil and waste as a best management practice to reduce P leaching.;Soil solution P concentrations were monitored at 45, 90, and 135 cm depths for 20 months in Autryville and Blanton soils under grazed pasture that had received swine waste for more than 20 years. Maximum soil solution P concentrations at 45 cm were in excess of 18 mg L−1 in both soils. Soil solution P concentrations at 90 cm in the Blanton soil were similar to that at 45 cm, indicating low P sorption. However, soil solution P concentrations at 90 cm in the Autryville soil averaged 0.05 mg L−1 compared to 10 mg L−1 at 45 cm. A split-line model related soil solution P concentration to the degree of P saturation (DPS), identifying a change point at 45% DPS. Phosphorus leaching losses were as high as 100 kg ha−1 yr−1 passing through 45 cm in the Autryville soil but less than 1 kg ha−1 yr −1 passing through 135 cm.;Modifying GLEAMS with the Langmuir equation to partition labile P between adsorbed and solution phases improved predictions of percolate P concentrations and soil P accumulation and increased model sensitivity to changes in crop and P management. (Abstract shortened by UMI.).