EFFECTS OF SELECTED MANURE SOURCES ON RUNOFF, SOIL LOSS, AND NUTRIENT TRANSPORT

Soil erosion models are becoming increasingly accurate and now can simulate a variety of surface covers which can lessen erosion by reducing detachment and movement of soil particles. Currently, there is limited data on the effects of animal manure on soil erosion. Most process-based models credit animal manure as crop residue cover. Thus, there is a need for bench studies under laboratory conditions, as well as field studies to determine the effects manure applications have on runoff and sediment loss. Rainfall simulation studies were conducted to evaluate the influence of different animal manures on runoff, sediment yield, and nutrient loss using undisturbed soil monoliths placed in perforated trays. The soil was collected from fields managed under long-term no-till and a conventional till for over 15 years. Poultry litter, solid dairy manure, liquid swine manure, liquid dairy manure applied to the experimental units were compared to a no manure treatment. Generally, sediment yield and runoff amounts were reduced following manure application regardless of source (averaged across all rainfall events and manure rates), with reductions generally occurring with increasing rates of manure. When evaluating each rainfall event separately, runoff increased with increasing rates of manure for the liquid dairy manure only in the initial rainfall simulation events due to surface sealing. However, the effects of surface sealing decreased from the first rainfall simulation event to the third event. Sediment yield tended to be higher in conventional till versus no-till (only evaluated with liquid dairy manure); however, the addition of manure tended to be more effective at reducing sediment loss with conventional till. Dissolved reactive P, NH4-N, and NO3-N levels in the runoff effluent increased for all of the manure sources with increasing rates of manure. These results suggest that manure applications can reduce soil loss, especially from the conventionally-tilled treatment.