Three compounds are responsible for generating two-thirds of the objectionable odors from beef manure, researchers with USDA's Agricultural Research Service have found.
ARS agricultural engineers Bryan Woodbury and John Gilley completed the research, which could help with developing techniques for controlling objectionable odors from manure used to amend crop fields.
Woodbury and Gilley's study not only reviewed odorous compounds in beef manure, it also evaluated how land application practices, diet, soil moisture and application procedures affect odor emissions.
The team used manure collected from feedlot pens where cattle consumed diets containing 0, 10, or 30 percent wet distillers grain solubles. The scientists also evaluated two application methods—no-till surface manure application or disk tillage that incorporated manure into the soil—and collected air samples before and after water was added to the soil to assess the effect of moisture levels on emissions.
Beef cattle manure was applied at levels that provided 135 pounds of nitrogen per acre, which met the 1-year nitrogen requirement for corn. After collecting and analyzing the air samples, the researchers determined that two volatile fatty acids—isovaleric acid and butyric acid—and the aromatic compound 4-methylphenol were responsible for over two-thirds of detectable beef manure odors.
Most of these odors were released within 24 hours after manure was applied to the soil, the research found.
Incorporating the manure into the soil and irrigating afterwards reduced most of the odor compounds that were measured. But the manure needed to be incorporated almost immediately after being applied to obtain the most effective odor mitigation.
The importance of tilling manure into soil was highlighted by emission measurements the researchers obtained for 4-methylphenol. The greatest emissions of this compound occurred from dry soils on no-till plots and were sometimes as much as 10 times greater than similar emissions from tilled soils.
Read more about the research on the ARS website.