Laboratory estimates of trace gas emissions following surface application and injection of cattle slurry

Applying cattle slurry to soil may induce emissions of the greenhouse gases N2O and CH4. Our objective was to determine the effects of different application techniques (surface application and slit injection) of cattle (Bostaurus) slurry on the decomposition of slurry organic matter and the emissions of N2O and CH4. The effects of slurry application (43.6 m(3) ha(-1)) were studied for 9 wk under controlled laboratory conditions using a soil microcosm system with automated monitoring of the CO2, N2O, and CH4 fluxes, The soil used was a silty loam (Ap horizon of a cambisol) with a constant water-filled pore space of 67% during the experiment. About 38% of the organic matter applied with the slurry was decomposed within 9 wk. Production of CO2 was not affected by the application technique. Emissions of N2O and CN4 from the injected slurry were significantly higher than from the surface-applied slurry, probably because of restricted aeration at the injected-slurry treatment. Total N2O-N emissions were 0.2% (surface application) and 3.3% (slit injection) of the slurry N added, Methane emission occurred only during the first Few days followimg application. The total net nux of CH4-C for 2 wk was -12 g ha(-1) for the control (CH4 uptake), 2 g ha(-1) far the surface-applied slurry, and 39 g ha(-1) for the injected slurry. Slurry injection, which is recommended to reduce NH3 volatilization, appears to increase emissions of the greenhouse gases N2O and CH4 from the fertilized fields.