Effects of biochar at different pyrolysis temperatures on reduction and control of nitrogen loss in sheep manure composting process

High temperature aerobic composting is one of the most economical and feasible methods to produce organic fertilizer from agricultural waste. It is not only conducive to the recycling and reuse of agricultural waste biomass, but also conducive to replacing chemical fertilizers and reducing the use of fertilizer in farmland. However, serious nitrogen loss is common in the process of composting, which reduces the agricultural value of composting products and increases the pressure of environmental pollution. Therefore, nitrogen fixation measures to enhance the composting process are the key technical links to realize the virtuous circle of agriculture, rural ecology and economy. Biochar is a kind of highly aromatic refractory solid material made from waste biomass inside and outside farmland under high-temperature anaerobic conditions. It has huge specific surface area, porous structure, carboxyl group, hydroxyl group, phenolic hydroxyl group and other unique properties. It has high thermal stability and strong adsorption capacity. To study the effective control of nitrogen loss in high temperature compost technology, biochar preparation of rice husk with two different pyrolytic temperature biochar for compost additives, mixed with sheep droppings, edible fungi residue, carried out composting trials of 43 days for composting engineering application of biochar control nitrogen loss and improve the quality of compost to provide technical support and theoretical basis. Three treatments were set up. The mixture of sheep manure and edible fungus residue fresh weight ratio at 9: 1 was used as the preparation material, the pyrolysis biochar at 450 and 650℃ (accounting for 15% of the fresh weight of the preparation material) was added to the preparation material for B1 and B2 treatment, and the unpyrolyzed rice husk (such as volume of biochar) was added to the preparation material for CK treatment. During the experiment, the changes of composting body temperature, NH3 volatilization, N2O emission, pH value and other parameters were monitored, and the nitrogen retention effect of biochar in composting at different pyrolysis temperatures was analyzed. The results showed that B1 and B2 treatment promoted the rapid rise of the initial temperature of composting, and the time needed for the first temperature rise to 55℃ was 2 and 6 days shorter than CK, respectively. The effect of B2 treatment was better than that of B1 treatment in promoting temperature rise and increasing temperature. After composting for 43 d, the NH3 volatilized accumulations treated by CK, B1 and B2 were 378.12, 117.22 and 94.16 mg/kg, respectively; the N2O emission accumulations were 13.9, 26.3 and 23.6 mg/kg, respectively; the nitrogen loss rates were 47.8%, 34.1% and 30.5%, respectively. B1, B2 treatment increased the composting body N2O emissions, reduces the composting body NH3 volatilization, cumulative N2O emissions in the composting process is far less than NH3 volatilization accumulations, adding biochar on composting process of nitrogen loss show the positive reduction control action, B1, B2 treatment of nitrogen loss rate than CK treatment was reduced by 28.66% and 36.19%, respectively, B1, B2 treatment between the difference was not significant (P>0.05). Based on the indexes such as rapid increase of reactor temperature and control of nitrogen loss, the nitrogen-preserving effect of B2 treatment was better than that of B1 treatment in the process of sheep manure composting. In the composting project, biochar was used to reduce nitrogen loss and improve composting quality, and the pyrolysis temperature of 650℃ was optimized to prepare biochar. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.