Influence of Manure Application Method On Odor Emissions.

Manure application in no-till and forage systems has traditionally involved surface spreading and significant odor emissions. Five liquid dairy manure application methods were evaluated using field olfactometry at <1 h, 2-4 h, and ~24 h after manure spreading. To minimize variability associated with source distance and wind, a 3-m swath of dairy slurry was applied in 61-m diameter rings to grassland. Field olfactometer instruments were used to collect dilution-to-threshold (D/T) observations from the center of each ring using four odor assessors taking four consecutive readings over a 10-min period. The Best Estimate Threshold D/T (BET₁₀) was determined for each method and an untreated control. Whole air samples were simultaneously collected for laboratory dynamic olfactometry evaluation using the triangular forced-choice (TFC) method. The BET₁₀ of composited data for all measurement times showed D/T levels decreased in the following order (a = 0.05): surface broadcast > aeration infiltration > surface + chisel incorporation > direct ground injection » shallow disk injection > control, which was correlated (r = 0.83) with laboratory TFC odor panel results. Odor levels 24 hr after direct ground injection were statistically indistinguishable from the untreated controls. Odors were correlated with visual estimates of the amount of manure remaining on the soil surface.