Effects of biochar and straw on greenhouse gas fluxes of corn fields in arid regions

Biochar refers to a kind of stable and carbon-rich solid matter, generally composed of biomass and fertilizers, such as litter and crop straw, which have been pyrolyzed and carbonized under high temperatures in either a completely anaerobic or partially anoxic state. To explore the effects of biochar and straw returning on the greenhouse gas fluxes of corn fields in arid areas, an experiment was conducted on a corn field in the Horqin District, Inner Mongolia. A static chamber-gas chromatography (GC) technique was used to conduct in situ observations on greenhouse gas (CO₂, CH₄, and N₂O) fluxes under different experimental treatments. These treatments included different application rates of biochar:0 (CK), 15 (C15), 30 (C30), and 45 t·hm^-2 (C45); and straw returning (SNPK). For the experiments, the global warming potential (GWP) and greenhouse gas intensity (GHGI) during the growing season were estimated. The results showed that the addition of biochar could significantly reduce the soil CO₂ and N₂O emissions. During the growing season, the CO₂ fluxes in the C15, C30, C45, and SNPK treatments decreased by 21.16%, 14.34%, 17.02%, and 19.93%, respectively. Among these treatments, C15 exhibited the best emission reduction effect. Compared with CK, the N₂O fluxes of C15, C30, C45, and SNPK reduced by 24.42%, 56.83%, 86.25%, and 28.28%, respectively. With the increase in biochar rates, the inhibition effect on N₂O emissions increased. Among the treatments, C45 provided the greatest reduction in emissions. Appropriate addition of biochar could promote the soil to absorb CH₄. Compared with CK, the soil CH₄ absorption of C15, C30, and SNPK increased by 56.62%, 32.05%, and 40.35%, respectively. The CH₄ absorption of C45 decreased by 81.36% compared with CK. Excessive biochar could cause less CH₄ absorption in the soil. There was a positive correlation between soil CO₂ flux, temperature, and moisture during the growing season. The CH₄ and N₂O fluxes of CK, C15, and SNPK were significantly correlated with the soil temperature and moisture during the growing season. However, the CH₄ and N₂O fluxes of C30 and C45 did not exhibit a significant correlation with the soil temperature or moisture during the growing season. The addition of biochar and straw returning to the field had a significant effect on increasing the corn yield and reducing the GWP and GHGI in the farmlands. Biochar and straw returning both effectively increased the corn yield in the Horqin District. The corn yield increased as the amount of biochar increased. From the perspective of the GWP, a biochar rate of 15 t·hm^-2 had the best overall effect on reducing greenhouse gas emissions, similar to the SNPK treatment. From the perspective of the GHGI, biochar and straw returning had certain economic benefits and significant reducing-effects of greenhouse gas emissions. Among the different treatments investigated, 15 t·hm^-2 of biochar had the highest comprehensive benefits, and the C45 and SNPK treatments were slightly inferior to C15, but higher than C30. Therefore, from the perspectives of comprehensive economic benefits and environmental factors, it was suggested that 15 t·hm^-2 of biochar should be added to the farmlands in Horqin when growing corn. If biochar was not available, straw returning can also be considered to achieve an increase in corn yields and decrease in greenhouse gas emissions.