Incorporating crop residues and biochar has received increasing attention as tools to mitigate atmospheric carbon dioxide (CO 2 ) emissions and promote soil carbon (C) sequestration. However, direct comparisons between biochar, torrefied biomass, and straw on both labile and recalcitrant soil organic matter (SOM) remain poorly understood. In this study, we explored the impact of biochars produced at different temperatures and torrefied biomass on the simple C substrates (glucose, amino acids), plant residues (Lolium perenne L.), and native SOM breakdown in soil using a 14 C labeling approach. Torrefied biomass and biochars produced from wheat straw at four contrasting pyrolysis temperatures (250, 350, 450, and 550°C) were incorporated into a sandy loam soil and their impact on C turnover compared to an unamended soil or one amended with unprocessed straw. Biochar, torrefied biomass, and straw application induced a shift in the soil microbial community size, activity, and structure with the greatest effects in the straw-amended soil. In addition, they also resulted in changes in microbial carbon use efficiency (CUE) leading to more substrate C being partitioned into catabolic processes. While overall the biochar, torrefied biomass, and straw addition increased soil respiration, it reduced the turnover rate of the simple C substrates, plant residues, and native SOM and had no appreciable effect on the turnover rate of the microbial biomass. The negative SOM priming was positively correlated with biochar production temperature. We therefore ascribe the increase in soil CO 2 efflux to biochar-derived C rather than that originating from SOM. In conclusion, the SOM priming magnitude is strongly influenced by both the soil organic C quality and the biochar properties. In comparison with straw, biochar has the greatest potential to promote soil C storage. However, straw and torrefied biomass may have other cobenefits which may make them more suitable as a CO 2 abatement strategy.

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Storing livestock manure is the primary stage of manure management where microbial processes and chemical reactions result in the release of methane (CH), nitrous oxide (NO), ammonia (NH), and carbon dioxide (CO). This study examined the reduction of CH emissions from slurry storage under two temperatures (cool [10°C] and warm [30°C]) when a glucose-rich substrate (brewing sugar) and activated effective microorganisms were applied at 10% (w/w) and 5% (v/w), respectively. Brewing sugar addition influenced microbial anaerobic respiration, resulting in a reduction of slurry pH to <5.0, through "self-acidification" caused by lactic acid production. Subsequently, CH emissions were significantly reduced by 87 and 99% in the cool and warm environments, respectively. The effective microorganism treatment did not change the chemical characteristics of the slurry but reduced CH emissions by 17 and 27% ( < 0.05) in the cool and warm environments, respectively. These results suggest that self-acidification after addition of a carbon source may be a promising alternative to slurry acidification using concentrated acids.

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Livestock slurry stores are a key source of ammonia (NH 3 ) and greenhouse gas (GHG) emissions. This study evaluated the potential to reduce NH 3 , CO 2 , CH 4 and N 2 O emissions by adding effective microorganisms (EM) and brewing sugar to beef cattle slurry in a replicated small-scale (1 litre slurry volume) experiment. The effect of EM and brewing sugar was explored at two concentrations (5 v / w and 10% w / w respectively) and in two environments (cold and warm) over a period of 30 days slurry storage. Greenhouse gas emissions were measured by taking headspace samples from the closed vessels over a 1 hour period, whilst relative NH 3 loss was quantified at the same time by placing an acid trap within the closed headspace. Brewing sugar addition induced 'selfacidification' of the slurry, via lactic acid production and accumulation, resulting in a decrease in slurry pH from pH 7.8 to <4.5. This was effective in lowering average NH 3 loss in the cold and warm environments by 40% and 70%, respectively. Methane emissions were also reduced following the addition of brewing sugar, by up to 75%, resulting in a reduction in the cumulative total GHG (N 2 O + CH 4 + CO 2 ) emission (expressed as CO 2 equivalent; CO 2 e) of 34% and 85%, respectively. The total greenhouse gas emission (CO 2 e) during slurry storage was dominated by CH 4 , representing at least 59% of total CO 2 e emitted. Effective microorganisms had little impact on NH 3 and GHG emission, and are not deemed a useful mitigation strategy for these gases.