Measurement of Greenhouse Gas Emissions of Methane and Carbon Dioxide Following Hog Manure Application to Winter Wheat as Affected by Manure Type and Manure Application Timing.

Hog manure is a valuable nutrient source in crop production but significant gaseous emissions of methane (CH₄) and carbon dioxide (CO₂) may occur at land-application. In a field trial study on a winter wheat crop (cv. Alchemy) at UCD Lyons Farm, gaseous emissions of CH₄ and CO₂ post land-application of hog manure were investigated. Two manures types were tested containing either a high (HN) or low (LN) nitrogen content. Grower-finisher pigs were assigned to one of two diets; a high crude protein (CP) diet (230g/kg) and a low CP diet (160g/kg) to generate the manures. In a 2 x 3 factorial experimental design the manure products were applied to a winter wheat crop at three timings; growth stage (G.S) 25 (T1), G.S 30-31 (T2) and G.S 37-39 (T3), at a rate of 30 m³/ha using a 6 meter band spread applicator to plots 30m x 24m. Gaseous fluxes were measured using the static chamber technique at 1-3 day intervals for 4 weeks post manure application. Significantly higher CH₄ emissions were measured from the HN manure treatments (19.41 vs. 11.88 gCH₄-C/ha/day) while CO₂ emissions were unaffected by manure type. Greatest CH₄ and CO₂ emissions were measured immediately post-manure application with loss rates returning to background levels within 24 hours. Highest CH₄ emissions were measured at T1 (range 3.81-28.92 gCH₄-C/ha/day) while peak CO₂ emissions were recorded at T3. Thus, it was concluded that CH₄ was formed during storage and a longer storage period prior to application at T1 (7 weeks) - led to higher emissions than those measured at T2 (3 weeks) and T3 (2 weeks) while higher CO₂ emissions were due to increased plant respiration rates at more advanced G.S. Therefore, dietary manipulation is a useful technique for CH₄ emission reduction while CO₂ emissions tended to increase with advancing growth stage.