Nitrous oxide and methane emission from a coarse-textured grassland soil receiving hog slurry

Methane (CH4) and nitrous oxide (N2O) are potent greenhouse gases (GHG) that contribute to global warming. The objectives of this study were to evaluate the impact of (i) timing of hog slurry application and (ii) a soil moisture gradient on CH4 and N2O emission from a coarse-textured, poorly drained, grassland soil. A factorial design with three treatments and two replicates was utilized. Treatments were: (i) zero manure (Control), (ii) hog slurry applied as a split application in the fall and spring (Split), each at a rate of 72 ± 8 kg plant available N ha−1, and (iii) a single application of hog slurry applied each spring at a rate of 148 ± 20 kg available N ha−1 (Single). To achieve the second objective, two parallel transects each with 30 chambers placed 9 m apart along a soil moisture gradient were utilized.Overall, CH4 and N2O emission from the manured treatments (Split and Single) were significantly higher (P < 0.001) compared to the Control. Over the 3 years, average CH4 emission from the Control, Split and Single treatments were 2.1, 6.8 and 5.3 g C ha−1 d−1, while N2O emission were 0.2, 2.2 and 4.9 g N ha−1 d−1, respectively. Similarly, cumulative CH4 and N2O emission and the combined CO2 equivalents from the manured treatments were significantly higher (P ≤ 0.01) than from the Control. Over the 3 years, mean cumulative CH4 emissions were 1.6, 3.5 and 2.7 kg C ha−1; cumulative N2O emission were 0.06, 0.4 and 0.8 kg N ha−1; while cumulative CO2 equivalent was 74, 279 and 459 kg CO2 ha−1 for Control, Split and Single treatments, respectively. Nitrous oxide contributed more to CO2-equivalent emission for the manure treatments with the ratio of N2O/CH4 CO2 equivalents being 0.7, 1.9 and 5 for the Control, Split and Single treatments, respectively. Soil water and NO3− content were the main determinants of both the type and quantity of GHG emitted, i.e., saturated soils with low NO3− produced highest CH4, while drier soils with high NO3− produced greatest N2O. Variation in height of the water table near the soil surface likely resulted in the high variability observed in CH4 emissions between replicates and years for individual treatments. These results suggest that: (i) split application of hog slurry to grassland has the potential to reduce emission of GHGs, in particular N2O, compared to applying all manure in spring, (ii) grassland soils with seasonally high water tables can be significant sources of CH4, and (iii) that CH4 emission increases with hog slurry application in this soil.