Nitrous oxide emissions from feces and synthetic urine of cattle grazing forage grass fertilized with hog slurry

Effects of hog slurry application to fertilized grassland on emissions of nitrous oxide (N2O) from feces and urine excreted by cattle grazing was determined. Feces from cattle grazing forage grass fertilized with two rates of plant available N from a hog slurry, (i) hog slurry as Split application in fall and spring, each 72 kg N/ha (Split), and (ii) hog slurry each spring at 148 kg N/ha (Single), and zero slurry (Control), were monitored in field experiments in 2004 and 2005. The slurry treatments resulted in total N of feces patches of 84 (Control), 86 (Split), and 106 g N/m2 (Single). Three synthetic urine treatments of (i) 136 g N/m2 (Low), (ii) 233 g N/m2 (Medium), and (iii) 329 g N/m2 (High) and no urine (Background) applied to simulate the range in levels possible for cattle grazing the grass fertilized with the slurry treatments were examined in 2005. Nitrous oxide emissions from feces of cattle grazing the Split and Single treatments were higher than Control. Cumulative N2O emissions from feces additions in the studies were 7, 31, and 91 mg N/m2 for the Control, Single and Split treatments, respectively. Nitrous oxide emissions from feces increased with feces NO3− and soil NH4+ concentrations, and decreased with feces and soil moisture. Cumulative N2O emissions from urine treatments were much higher than from feces, being 165, 534 and 694 mg/m2. Nitrous oxide emissions from urine increased with soil NO3−, NH4+ and NO2− concentrations and decreased with soil moisture. Nitrous oxide emissions estimated for excreta of grazing cattle were 27 g/kg of direct soil emissions for grassland receiving no slurry (Control) and 104 and 73 g/kg of direct emissions of the Split and Single slurry treatments. Findings indicate direct N2O emission estimates for hog cattle grazing production systems are enhanced more by hog slurry treatment than are emissions from excreta.