Global warming is profoundly altering soil freeze -thaw cycle (FTC) patterns, and the formation of different thicknesses and durations of snow cover by snowfall results in heterogeneity of environmental and biological factors, which can have complex effects on soil water and carbon cycle processes. In order to better develop rational regulation strategies to increase the potential of soil carbon sequestration and emission reductions under climate change conditions, a three-year in situ control trial of field snow was set up to simulate climate scenarios using two treatments: snow removal and natural snow. The effects of FTCs and biochar on soil CO 2 emission flux (CO 2 Flux) were analyzed by constructing a driven coupling model between soil hydrothermal environmental factors, unstable organic carbon components and stable organic carbon components. The results showed that CO 2 Flux decreased by 9.36% to 11.34% for 1% biochar treatment, while CO 2 Flux increased by 15.41% to 18.32% for 2% biochar treatment. Moreover, the snow removal treatment increased CO 2 Flux by 9.86% to 13.99% compared to the natural snow treatment. The snow during freezing and thawing has a dual effect on soil hydrothermal dynamics, with snow removal making the freeze -thaw action more intense in perturbing the soil carbon matrix, while the interfacial behavior of biochar with soil minerals protects the stability of the soil structure. Biochar reduces soil carbon emissions thanks to its highly stabilized components and unique surface structure, which enhances the carbon sequestration and emission reduction effect by increasing the proportion of inert organic carbon, promoting the formation of organic -inorganic complexes, and encapsulating and adsorbing soil organic matter. The results of the study can provide important theoretical support and practical models for the assessment of the environmental effects of biochar and the reduction of carbon sequestration in agriculture under climate change conditions.

When applied in agriculture, the solid carbonaceous residue of anoxic thermochemical conversion of biomass (biochar) has variable effects on soil, crop yields, and climate mitigation. Biochar can be added to soil as powder or as pellets. While powdered forms have demonstrated effects on crop yields, they may release coarse and fine particulate that can be transported into the atmosphere during production, packaging, storage, transport, and distribution. Biochar weathering and wind erosion may also cause the release of particles. Particulate matter (PM) released from biochar may have negative effects on human health and increase the atmospheric burden of shortwave absorbing black carbon aerosols with non-negligible effects on atmospheric radiative forcing. Pelletizing feedstock before the thermochemical conversion and moistening of biochar are expected to reduce the emission of PM in the processing and post-processing phases while also increasing the mean residence time of Carbon in soils. The impact of biochar formulation (pellet and non-pellet) on the release of coarse and fine particulate in wet and dry conditions was assessed in a laboratory experiment. In parallel, the effects of pellet and non-pellet formulations on growth and yield of processing tomato plants were tested in a pot experiment. Results show that pelletization and moistening substantially reduce the amount of fine particles released and are therefore practices that should be adopted to maximize the mitigation potential of biochar. A reduction of tomato yield was observed in pellet treatment, suggesting that the higher interface area of powdered biochar may boost productivity in the short term. This work points to the existence of a tradeoff between the short-term maximization of agronomic benefits and the minimization of harmful effects due to particulate release.

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.