Date of this Version
Proceedings of the Great Plains Soil Fertility Conference, Denver, Colorado, March 5-6, 2002, ed. Alan J. Schlegel.
Phosphorus (P) losses from agricultural land is a serious environmental issue because of the impact of P on freshwater eutrophication (McDowell, et al., 2001). The movement of P from soil to surface water is impacted by P input to soil and manure management practices that impact P transport processes. Twenty-one natural runoff plots were established to monitor the effect of time and method of composted beef feedlot manure application and feed P input on net losses of bio-available P and sediment in surface runoff. Reducing feed P inputs resulted in a 33% reduction in manure P content. Runoff losses of P were reduced in direct proportion to feed P inputs. Runoff volume and sediment losses were lowest in the year s of compost application and we observed that a longer time interval between compost application date and spring runoff season resulted in increase sediment, runoff and P loss. Bray-PI extractable soil P (0-15cm) increased from 27 ppm prior to compost application up to 400 ppm in direct proportion to manure P loading rate. Management criteria designed to assess the potential for landscape P loading (i.e. "P-index") correctly weight winter· applications as more hazardous than planting time applications. Results indicate that reduction of P input at the feedlot will have a long-term impact in reducing P loading to surface waters.