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

Tenuta, Mario, Mkhabela, Manasah, Tremorin, Denis, Coppi, Luca, Phipps, Graham, Flaten, Don, Ominski, Kim
Agriculture, ecosystems & environment 2010 v.138 no.1-2 pp. 35-43
grasslands, grassland soils, soil texture, nitrous oxide, methane, gas emissions, pig manure, greenhouse gases, application timing, soil water content, application rate, nitrogen, water table, liquid manure
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±8kgplantavailableNha⁻¹, and (iii) a single application of hog slurry applied each spring at a rate of 148±20kgavailableNha⁻¹ (Single). To achieve the second objective, two parallel transects each with 30 chambers placed 9m 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 5.3gCha⁻¹ d⁻¹, while N₂O emission were 0.2, 2.2 and 4.9gNha⁻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 2.7kgCha⁻¹; cumulative N₂O emission were 0.06, 0.4 and 0.8kgNha⁻¹; while cumulative CO₂ equivalent was 74, 279 and 459kgCO₂ 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.