Nitrous Oxide and Ammonia Emissions from Cattle Excreta on Shortgrass Steppe

Grazing cattle redistribute nitrogen (N) consumed in forage through urine and feces patches. The high concentration of N in these patches often exceeds the uptake demands of the local plant community, thereby providing ideal conditions for losses of reactive N. However, knowledge on nitrous oxide (N 2 O) and ammonia (NH 3 ) emissions from excretal patches on shortgrass steppe grassland is limited. We studied the effect of cattle urine (1002 kg N ha −1 ) and feces (1021 kg N ha −1 ) patches on N 2 O and NH 3 emissions in two sites with contrasting vegetation: (i) cool‐season (C3) ‘Bozoisky‐Select’ Russian wildrye [ Psathyrostachys juncea (Fisch.) Nevski], pasture (C3Past) and (ii) C4‐dominated native shortgrass steppe rangeland (C4SS). Nitrous oxide and NH 3 were measured using semi‐static and semi‐open chambers, respectively. Cumulative N 2 O emissions were 217 and 173% greater and cumulative volatile NH 3 emissions were 339 and 157% greater on C3Past compared with C4SS from the urine and feces treatments, respectively. Nitrous oxide emission factors were 0.20 and 0.05% for urine and 0.07 and 0.03% for feces on C3Past and C4SS, respectively. Our findings suggest that using the IPCC Tier 1 default emission factor (2%, 95% CI = 0.7–6%) to estimate N 2 O emissions from cattle excretal patches on shortgrass steppe grassland would result in a significant overestimation for these dryland systems. Ammonia emission factors were 35 and 10% for urine and 7 and 5% for feces on C3Past and C4SS, respectively. With the exception of the urine treatment on C3Past, observed NH 3 emissions were consistent with the IPCC Tier 1 default assumption that 20% (95% CI = 5–50%) of excretal N is volatilized as NH 3 +NO x . Core Ideas N 2 O emission factors from excreta (0.03–0.20%) were lower than the IPCC default (2%). Substantial N 2 O emissions were not observed from excreta until a month after application. NH 3 emission factors from cattle excreta ranged from 5 to 30% on shortgrass steppe. Elevated NH 3 volatilization from excreta persisted 78 d after treatment application. N 2 O and NH 3 emissions from excreta were greater on C3 pasture compared with C4 rangeland.