MEASUREMENT AND PREDICTION OF PHOSPHORUS TRANSPORT FROM SWINE MANURE AT THE WATERSHED SCALE

Authors: Sauer, Thomas; SREEMATKANDALAM, KALYANA - ISU; TIM, U - ISU; James, David; Hatfield, Jerry

Submitted to: International Symposium on Agricultural & Food Processing Wastes Proceeding
Publication Type: Proceedings
Publication Acceptance Date: 10/14/2003
Publication Date: 10/12/2003
Citation: SAUER, T.J., SREEMATKANDALAM, K.C., TIM, U.S., JAMES, D.E., HATFIELD, J.L. MEASUREMENT AND PREDICTION OF PHOSPHORUS TRANSPORT FROM SWINE MANURE AT THE WATERSHED SCALE. INTERNATIONAL SYMPOSIUM ON AGRICULTURAL & FOOD PROCESSING WASTES PROCEEDING. 2003. P. 535-541.

Interpretive Summary: Swine are typically produced at locations that have many thousands of animals in several large buildings. The manure generated by the swine contains nutrients that can be used to grow crops. However, if there is too much manure produced, it is often overapplied to the land and this leads to water quality problems if excessive nutrients are transported by runoff into streams and lakes. The purpose of this study was to measure the amount of phosphorus in the water draining from a watershed with intensive swine production and to use a model to predict how phosphorus transport might change if even more swine were produced in the watershed. Concentrations of phosphorus in the stream water were greatest during storm events and spring snow melt. Nearly equal amounts of phosphorus were found dissolved in the water and attached to sediment. Estimates of manure and fertilizer application indicated that only 35% of the phosporus applied to soils in the watershed was in manure, the rest came from commercial fertilizer. Model predictions showed that, if swine production continues to grow at a rate of 5% per year, phosphorus content in runoff could increase significantly in as little as five years. Management practices to reduce the amount of phosphorus in manure are available and, if used, could actually reduce the amount of manure phosphorus produced, even if swine production continues to increase. The findings of this study are important to swine producers as they demonstrate that practices are available to reduce the amount of phorphorus in swine manure applied to soil even as the density of swine production increases.

Technical Abstract: Livestock production facilities are coming under increased scrutiny with regard to transport of phosphorus (P) from fields receiving animal manures. The objective of this study was to measure and simulate how swine manure management affects P export from a row crop watershed with intensive swine production. Stream water sampling was conducted for one year at 14 locations within the Tipton Creek watershed in central Iowa. Geographic Information System (GIS) data layers (topography, soils, land use, and land cover) were prepared to facilitate simulations using the Agricultural Non-Point Source model (AGNPS). The average dissolved reactive (DRP) and total phosphorus (TP) concentrations in stream water from 41 sampling dates were 0.14 and 0.21 mg L-1, respectively. Total P export from the Tipton Creek watershed from April 1, 2000 to April 1, 2001 was estimated at 10.6 metric tons (Mg) for an average loss of 0.52 kg P ha-1 yr-1. Four rainfall events during the 2000 growing season and snowmelt in March 2001 were responsible for 91% of the P transport from the watershed. Using animal inventory numbers and standard P excretion values, swine manure was estimated to supply approximately 35% of the land-applied P. AGNPS simulations indicated that, without any changes in current management, a 40% increase in P transport in runoff events could occur in the next 5 years. However, a combination of diet manipulation and use of high available-P feedstuffs and/or phytase enzyme have been shown to reduce P excretion by as much as 50%. Adoption of these practices would likely prevent any increase in P production from swine facilities and potentially reduce P production compared to current levels.