Digging deep for ways to curb ammonia emissions

Dairy farmers can greatly reduce ammonia emissions from their production facilities by injecting liquid manure into crop fields below the soil surface, according to research by the U.S. Department of Agriculture (USDA).

These findings, which resulted from a study conducted by soil scientist April Leytem and agricultural engineer David Bjorneberg with USDA's Agricultural Research Service (ARS), could help Idaho dairy farmers increase nitrogen capture in the soil and protect air quality from agricultural ammonia emissions. ARS is USDA's principal intramural scientific research agency.

The scientists work at the ARS Northwest Irrigation and Soils Research Laboratory in Kimberly, Idaho, and conducted their study on four dairy farms in Idaho, a state where the number of milk cows has increased 88 percent in the last decade. They applied liquid dairy manure stored in containment lagoons either by surface broadcasting, using a rolling tine aerator to incorporate manure into the top four inches of the soil surface, or injecting the manure 12 inches below the soil surface.

Over the three-day study period, the greatest concentration of emissions was recorded during the 48 hours immediately following the manure applications, with the majority of emissions occurring within 24 hours. Surface broadcasts resulted in average ammonia concentrations of 0.17 milligrams of nitrogen per cubic meter, and shallow incorporation resulted in average
ammonia emission rates of 0.16 milligrams of nitrogen per cubic meter. Fields where manure had been amended using subsurface injection had average ammonia concentrations of 0.06 milligrams of nitrogen per cubic meter—65 percent lower than emission rates resulting from soil amendments via shallow incorporation or surface broadcast.

Leytem and Bjorneberg concluded that dairy farmers who use dairy manure to amend soils could best reduce ammonia emissions by using subsurface injection, and that immediately incorporating manure deep into the soils during its application can limit losses of manure nitrogen from ammonia volatilization.