A microbial ecosystem enhanced by regulating soil carbon and nitrogen balance using biochar and nitrogen fertiliser five years after application

Indiscriminate use of nitrogen fertiliser (NF) is a barrier to improving soil quality and crop yields. However, the effect of the combined use of biochar and NF on soil microbial ecosystem (SME) and crop yields is unknown. In the western Liaohe Plain of China, we conducted a five-year field experiment to assess the effects of the combination of biochar and NF on soil structure, C-to-N ratio (CNR), microbial biomass, and spring maize yield. Biochar and NF were applied at 0, 8, 16, and 24 t/ha and 0, 150, and 300 kg/ha, respectively. Compared to their individual use, combination of biochar and NF resulted in a solid–liquid–gas ratio closer to the ideal value. Biochar alone and in combination with NF significantly increased the C, N, and CNR. Moderate use of biochar and NF resulted in the best biological and chemical properties of the soil. A comprehensive evaluation of soil and maize revealed that SME was enhanced by applying biochar and NF at moderate levels (8 t/ha and 150 kg/ha, respectively). The highest yield represents a 24.25% increase compared to the control. Moderate use of biochar and NF has potential as a valuable strategy in regions with similar climate.