|Parsons, John - N. CAROLINA STATE UNIV.|
|Mikkelsen, Robert - N. CAROLINA STATE UNIV.|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2005
Publication Date: November 1, 2005
Citation: Nelson, N.O., Parsons, J.E., Mikkelsen, R.L. 2005. Field-scale evaluation of phosphorus leaching in acid sandy soils receiving swine waste. Journal of Environmental Quality. 34:2024-2035. Interpretive Summary: Waste produced on large-scale swine farms is often applied to soil surrounding the farm, which adds more phosphorus (P) than what is removed by the growing crops. Under most agricultural practices, P sticks to the soil and does not move very easily with water percolating through the soil. Excess P application to soils can result in vertical transportation (leaching) of P through the soil into shallow groundwater, where it could be transported to nearby streams or rivers. Phosphorus inputs to streams and rivers can degrade water quality. This study quantifies the amount of P leached through two different soils that have received swine waste applications for over 20 years. Phosphorus concentrations in soil solution were also related to soil chemicals properties. Results show that P movement past 45 cm deep was equal to or greater than the amount of P applied to the soils. In one soil, P movement past 90 cm deep was the same as P movement past 45 cm. Both soils had very small amounts of P moving past 135 cm deep. This demonstrates that P leaching can occur when P applications exceed crop removal. This study also shows that P concentrations in soil solution can be predicted based on soil chemical properties.
Technical Abstract: Excess phosphorus applied to soils with low P adsorption capacities can enter surface water via leaching and subsurface transport, thereby negatively impacting water quality. The protection of water quality and sustainability of animal production are dependent on accurate descriptions of waste management and soil property effects on P leaching. The objectives of this study were to monitor P leaching throughout the profile of soils with a long-term history of waste application and various degrees of P saturation, relate soil solution P concentrations to soil P status, and quantify P leaching losses with respect to P additions. 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 exceeded 18 mg/L 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 compared to 10 mg/L at 45 cm, indicating significant P adsorption. A split-line model related soil solution P concentration to the degree of P saturation (DPS), identifying a change point at 45% DPS. Vertical P movement exceeded 90 kg/ha/yr at 45 cm in the Autryville soil but was less than 0.2 kg/ha/yr at 135 cm. Phosphorus movement past 45 cm in the Autryville soil was in excess of surplus P additions, with P desorption contributing up to 50% of P leaching losses. Although high soil solution P concentrations and substantial vertical P movement occurred in soil horizons where DPS exceeded 90%, soil solution P concentrations remained very low in underlying soil horizons with DPS < 45%, emphasizing the impact of sub-soil properties on P leaching losses in sandy soils.