Net-mineralization of organic matter and greenhouse gas emissions from Quebracho tannin-enriched manure applied to acidic and alkaline soils

Background Mitigation strategies to reduce greenhouse gas emissions, ammonia volatilization, and nitrate leaching from agriculture are important for the management of environmental pollution and climate change. Tannins, which are water-soluble polyphenolic compounds, were found to reduce emissions in animal husbandry systems when supplemented to ruminant diets. Aim Two laboratory incubation experiments were conducted to investigate the effects of Quebracho tannin-enriched manure on carbon (C) and nitrogen (N) mineralization processes, and greenhouse gas emissions from three different soils (sandy moderate acidic, sandy alkaline, and loamy alkaline). Methods In the two incubation experiments of 4 and 9 weeks, soil samples were analyzed for K2SO4 extractable C and N, NH4+ and NO3-, microbial biomass C, and pH. In the main experiment emissions of CO2, N2O, and NH3 were regularly monitored. Results Three days after manure application, the CO2 emissions of the three soils were reduced by 26%-37% and N2O by 80%-92% in tannin-enriched manure treatments compared with tannin-free manure. However, subsequent cumulative CO2 and N2O emissions were only reduced in the loamy alkaline soil applied with tannin-enriched manure. Also, in the initial 4 weeks net-mineralization after manure application was significantly lower in soils applied with tannin-enriched manure, reflecting an immobilization of N compared with tannin-free manure in the short term or an inhibition of the mineralization process by physicochemical complexation of proteins or inhibition of enzyme activities in the long term. In both experiments, NO3- was by 23%-95% lower in the three soils after 3-9 weeks compared with tannin-free manure. Conclusion These results highlight the mitigation potential of tannin-enriched manure on soil N leaching, and suggest that greenhouse gas emissions may be increased depending on soil properties.