Effects of biochar and nitrogen fertilizer on microbial communities, CO2 emissions, and organic carbon content in soil

Abstract

This study examined the effects of biochar and nitrogen fertilizer application on CO2 emissions, microbial communities, and soil organic carbon (SOC) in irrigated wheat fields through a 3-year field experiment. Eight treatment groups were established for this study: (1) CK, without fertilizer or biochar, (2) N1 group, with nitrogen fertilizer application (300 kg/ha), (3) B group, with biochar application (20 t/ha), (4) BN1 group, with nitrogen fertilizer and biochar application, (5) N2, with a 15% reduction in nitrogen fertilizer (255 kg/ha), (6) BN2, with a 15% reduction in nitrogen fertilizer + biochar. (7) N3, with a 30% reduction in nitrogen fertilizer (210 kg/ha); and (8) BN3, with a 30% reduction in nitrogen fertilizer + biochar. The results revealed an increase in active organic carbon (AOC) and SOC contents of soil after the addition of biochar and N fertilizer, particularly with their combined application. In the BN2 treatment, SOC and AOC contents reached 27.48 g/kg and 1.47 g/kg, representing increases of 3.04% and 30.91%, respectively, compared to N1. In comparison to CK, cumulative CO2 emissions increased by 9–48% with the addition of both biochar and nitrogen fertilizer, possibly due to biochar’s influence on the composition and functional diversity of soil microbial communities. The functional diversity of soil microbes in the BN1 group differed significantly from that in CK (p < 0.01). In the B group, soil microbial attributes were lower than those in BN1, BN2, and BN3 groups. Furthermore, the bulk density of biochar-amended soil was 0.19 g/cm3 lower than that of untreated soil in CK. Overall, the combination of biochar application and a nitrogen dose of 255 kg/ha emerged as the most effective strategy for irrigated wheat fields in northern Xinjiang, enhancing SOC content while reducing carbon emissions. However, further research is required to assess the long-term effects of this approach on soil health and sustainability.