Snow cover manipulation in agricultural fields: as an option for mitigating greenhouse gas emissions

Short-term N2O emission occurs in relation to snowmelt within seasonally frozen soil. To understand the effects of changing winter climates on the N2O flux, snow cover manipulation experiments are useful. In Japan, snow cover manipulation is practiced by farmers to improve agricultural yield and is executed either by applying a broadcast of blackish agent onto the snow cover, which leads to faster snow-melting thereby extending the crop-growing season, or by snow cover removal/re-accumulation, leading to an enhanced soil frost depth for weed management. Implementation of these practices involves using an amount of fossil fuel, in addition to influencing soil-derived N2O emissions, therefore, the load factors of snow cover management practices per unit area of agricultural field were estimated in this study. Field data including micrometeorological conditions, ground surface flux of N2O, and amount of fossil fuel consumed during machinery operation for management practices, were obtained at two sites in Hokkaido over 2 years (2008-2010). Fuel consumption for the field spreading was found to be unexpectedly small (0.017 Mg CO2 eq ha(-1)). It was therefore suggested that acceleration of snowmelt may have the potential to reduce net greenhouse gas emissions if the agent used is a low-degradable C-rich material, such as charcoal. For soil frost control, the fossil fuel consumption during a set of snow cover removal/re-accumulation (estimated as 0.052 Mg CO2 eq ha(-1)) is discussed, together with the relationship between possible mechanisms causing stimulation of N2O production in frozen soil and inherent large differences in N2O flux among sites.