Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: 11/9/2000
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: Phosphorus (P) losses from land-applied manure (LAM) contribute to nonpoint source pollution of surface waters. Dietary P levels influence P concentrations in animal manures and may affect P losses from LAM. This study's objective was to determine effects of dairy diet P concentration on P losses in runoff from LAM. Dairy manures with preliminary P concentrations of 4.8 and 12.8 g/kg from two dietary P levels were applied at 56 wet mg/ha (40 and 108 kg P/ha, respectively) to a silt loam soil. High-P diet manure was also applied at 21 wet mg/ha (40 kg P/ha) to provide a P rate equivalent to the low-P diet manure. Plots received simulated rainfall (75 mm/hr) before corn (Zea mays L.) planting in Jun and at harvest in Oct 1999. Runoff was analyzed for dissolved reactive P (DRP), bioavailable P, total P, and sediment concentration. Natural runoff from the same plots was collected from Nov 1999 - Jul 2000, and analyzed for DRP. At equivalent manure rates, DRP in Jun runoff from the high-P diet manure was about 10 times higher (2.84 vs 0.30 mg/L) than the low-P diet manure, and 4 times higher (1.18 vs 0.30 mg/L) when applied at equivalent P rates. P concentrations in Oct runoff and Nov-Jul natural runoff were less (0.02-1.69 mg/L), but treatment effects were the same as for Jun runoff. Thus, excessive inorganic P in dairy diets increases potential for P loss in runoff from LAM. Also, P's effects on potential runoff losses from LAM should be considered in P-indexing and nutrient management planning.