CH4 FLUXES FROM A SOIL AMENDED WITH DAIRY-CATTLE MANURE AND AMMONIUM

Dairy cows and heifers in Quebec and Ontario produce 19 Mt of manure a nnually. Most of this manure is applied to soils and may influence the atmospheric loading of greenhouse gases such as CH4. In this study, s oil surface CH4 fluxes were measured 36 times during the snow-free sea son of 1993, and 28 times in 1994, on plots fertilized with organic or inorganic-N. In 1993, stockpiled dairy cattle manure was applied at r ates of 0, 56 and 112 Mg ha(-1). In 1994, the treatments were: zero N, 100 Mg ha(-1) of stockpiled dairy cattle manure, 100 Mg ha(-1) of com posted dairy cattle manure and 200 kg N ha(-1) as ammonium nitrate. Me thane fluxes (-0.012 to 0.004 mg m(-2) h(-1)) were usually higher (les s negative) on manured than on unmanured plots, but the differences we re not statistically significant. No significant effect of mineral-N f ertilization was observed as the ammonium nitrate treatment showed upt ake rates similar to those of the control. In 1993, episodic above-amb ient CH4 concentrations were measured at 0.15 m (8 ppmv) and 0.05 m (2 .7 ppmv) using stationary air probes, bur were not associated with sig nificant CH4 emissions at the soil surface. This observation suggested that CH4 produced in the soil was oxidized by methane-consuming organ isms as it diffused towards the surface. Methane concentrations in soi l air were higher in manured than in unmanured plots during most of th e 1994 snow-free season, but were similar late in the season when solu ble organic C concentrations in the manured plots returned to levels m easured in the control plots early in the season. The results of this study indicate that the application of quantities up to 100 Mg has of dairy cattle manure to a soil under maize is not likely to have a larg e impact on the net exchange of CH4 between the soil and the atmospher e in central Canada.