Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 21, 2000
Publication Date: N/A
Interpretive Summary: Animal manure contains plant nutrients (like phosphorus) and is used as a crop fertilizer. The use of animal manure as a fertilizer is a good way for the farmer to save money. However, if animal manure is over-applied, nutrients such as phosphorus will accumulate in the soil. If soil enriched in phosphorus is transported to surface water by runoff or ground water, aquatic weed and algae growth will increase and limit the use of the water Concern about this situation prompted us to examine phosphorus levels in soil and ground water in a spray field that has received some intensive swine manure loading rates (initially much greater than standard practices) for about 10 years. We found that in a spray field that has received intensive swine manure at rates atypical to standard amounts, phosphorus had accumulated in the soil and moved to the shallow ground water. Our results show that if a spray field receives intensive (much greater than normal loading rates) manure application, phosphorus can accumulate in the soil and move to the shallow ground water.
Technical Abstract: Understanding the movement of phosphorus (P) in soils receiving heavy animal waste application is very important for nonpoint pollution control. We investigated both P accumulation in soil and P movement to ground water in a Coastal Plain spray field after 10 yrs of intensive (initially much greater than standard practice) swine manure application. Phosphorus was measured in soil cores collected in 1991 (4 yrs after manure application) and 1997 (10 yrs after application) as well as P in ground water wells. Spatial variation in P accumulation and movement was also examined across the spray field by use of additional soil cores collected in 1997. Soil-P was measured as total phosphorus (TP) and as Mehlich 3 P (M3P), while dissolvable P (DP) was measured in ground water. Soil and ground water from a contiguous site that has received no manure was sampled for background P concentrations. Surface soils (0 to 15 cm deep) had high concentrations of M3P (376 to 436 mg P/kg) and subsurface soils (107 cm) also had high amounts of M3P (151 mg P/kg). Similar results were found in cores collected across the spray field. Control soils that had received no swine manure were very low (< 10 mg P/kg) in M3P throughout the soil profile. Phosphorus in ground water within the spray field was initially (1992 to 1995) very low in DP (< 40 ug P/L), but by late 1996, the DP concentrations in a few wells increased substantially (40 to 480 ug P/L). In contrast, ground water from two control wells (1994 to 1998) was low in DP (< 40 ug P/L). Our results indicate that although atypical, long-term, intensive swine manure applications can result in substantial soil P accumulation and P movement to shallow ground water beneath the spray field.