Modeling Rainfall-Induced Release of Manure Constituents From Surface-Applied Liquid Dairy Manure.

Release kinetics of manure constituents (MC) is an important mechanism affecting overland and subsurface transport of manure-borne contaminants. Present release models adequately describe the rainfall-induced release of MC from surface-applied solid manure, but these models are not applicable for liquid manure because they do not account for the manure infiltration into the soil. Our objective was to develop and test a model for release of MC from liquid manure applied on vegetated soil surface. Manure was applied onto five 40 x 25 cm runoff boxes that were filled with the commercial turfgrass sod and tilted to create 4% slope. The boxes were irrigated for 90 min, and runoff was analyzed for chloride, fecal coliforms, enterococci, and water-soluble phosphorus. Runoff from the boxes ranged from 9% to 47% of total irrigation, and resulted in bacteria recovery from 1% to 21% and soluble MC from 0.6% to 15% with runoff water. The Bradford-Schijven release model was modified to account for the decrease of manure mass with time due to infiltration of liquid phase into the soil. Both original and modified models were fitted to the experimental data. Substantially more accurate results were obtained with the modified model.