1187 Effect of temperature on ammonia emissions from feedlot cattle manure

Livestock feeding operations are the largest contributor to anthropogenic ammonia emissions affecting air quality and terrestrial and aquatic ecosystems. Ammonia emissions are highly temperature dependent and can be expected to vary through the production cycle from the major cattle producing regions of Western Canada that experience environmental extremes of cold winters and hot, dry summers. A study was conducted to simulate and quantify the effects of temperature on ammonia emissions from manure of feedlot cattle. Fresh feces and urine were collected separately for 24 h from eight beef heifers fed high concentrate, barley grain-based diets (14.8% CP). Urine was collected using bladder catheters into collection vessels submerged in an ice-slurry. Feces and urine were each pooled, sampled for chemical composition, divided into subsamples, and frozen. Feces and urine were thawed, equilibrated to treatment temperatures, combined to constitute manure (1:1 wt/wt wet basis), and ∼2.25 kg of the manure were incubated in each of four open flow-through chambers. Chambers were housed within a walk-in controlled environment room with a fresh air exchange rate to prevent build-up of gases. Air flow through the chambers was 1.5 m/s and was subsampled by pumping 200 mL/min through sorbent tubes fitted on the inlet and exhaust ports at 24, 48, 72, and 96 h at temperatures of 5, 10, 15, 20, and 25°C. Flux and cumulative NH3–N emissions were analyzed with a mixed model with experimental temperature as a fixed effect and chamber as a random effect and the experimental unit. Orthogonal contrasts were applied to determine linear and quadratic effects of temperature on emissions. Manure contained 17.6% DM and 1.12% N (as-is basis) of which 54.2% was urea-N. Increasing the temperature from 5 to 25°C increased the NH3–N flux (g N/m2) and cumulative emissions (g N/96 h, % of total N, and % of urea-N; linear and quadratic, P < 0.001). Cumulative NH3–N emissions expressed as a percentage of total manure N for the 96-h incubations were 6.3, 21.2, and 30.8% at temperatures of 5, 15, and 25°C, respectively. Cumulative NH3–N emissions expressed as a percentage of manure urea-N were 20.3, 38.3, and 58.7% for 5, 15, and 25°C, respectively. Temperature had a marked effect on volatilization of NH3–N from feedlot manure and was reduced by 75% as temperature decreased from 15 to 5°C and increased by 50% as temperature increased from 15 to 25°C.