EMISSION OF VOLATILE ORGANIC COMPOUNDS FROM LAND-APPLIED BEEF CATTLE MANURE AS AFFECTED BY APPLICATION METHOD, DIET, AND SOIL WATER CONDITION

Land application of beef cattle manure may result in the emission of volatile organic compounds (VOC). This study was conducted to evaluate the effects of diet, land application method, soil water condition, and time since manure application on VOC emissions. Manure was collected from feedlot pens where cattle were fed diets containing 0%, 10%, or 30% wet distillers grains with solubles (WDGS). The effects of manure application method (surface-applied or incorporated) and soil water condition (saturated or wet) on VOC emissions were measured over a 48 h period. Heptanoic, hexanoic, isobutyric, and isovaleric acids contributed 23.5%, 17.6%, 9.26%, and 3.39% (0.034, 0.258, 0.030, and 0.014 pg m(-2) min(-1)), respectively, to total odor activity values (OAV). The aromatics indole and skatole contributed 14.7% and 8.84%, (0.005 and 0.0004 pg m(-2) min(-1)), respectively, to total OAV. Dimethyl disulfide (DMDS) contributed 9.50% (0.013 pg m(-2) min(-1)) and dimethyl trisulfide (DMTS) contributed 5.68% (0.030 pg m(-2) min(-1)) to total OAV. Emissions of the sulfur compounds (DMDS and DMTS) were substantially greater for the 30% WDGS diet. With the exception of heptanoic acid, flux measurements were greater from the plots where manure was surface-applied than from the plots where manure was incorporated. Emissions of each VOC were greater on the first day following manure application when a saturated soil water condition was present. VOC flux values were found to rapidly decrease following manure application. Effective best management practices for reducing VOC emissions are to incorporate manure soon after application and to delay land application when there is a high probability of rainfall.