Soil CO2 emission reduction with no-tillage and medium nitrogen fertilizer applications in semi-humid maize cropland in North China Plain

To better understand the effects of tillage practices and nitrogen (N) fertilizer applications on the microbial-mediated soil CO2 emissions in the maize fields, a four-year (2018–2021) experiment was performed to compare conventional tillage (CT) and no-tillage (NT) in combination with different N rates (high N (HN) and medium N (MN) applications) on the temporal dynamics of CO2 emissions in the soil. The results showed that soil CO2 emissions were decreased by 10.3%24.5% and 18.9%31.8% under NT and MN as compared to CT and HN, respectively. The lowest and highest soil cumulative CO2 emissions occurred in the NTMN treatment (a recommended pattern) and CTHN treatment (an extensively used pattern locally), respectively. Relative to CT and HN, NT and MN increased the grain yields by 1.4%9.0% and 7.0%, respectively. NT decreased bacterial richness and alpha-diversity by 9.8% and 6.2% at the taxonomic level than CT. Meanwhile, NTMN reduced fungal diversity by 0.7%, bacterial diversity by 3.4% and bacterial richness by 0.3% compared to CTHN. NT and MN inhibited metabolic processes associated with carbon (C) cycling and enhanced C fixation pathways in prokaryotes. NTMN treatment reduced substrate availability and energy sources for fungal and bacterial activities by altering soil biochemistry, further decreasing fungal and bacterial diversity, suppressing soil CO2 emissions, and increasing yields, which were in turn enhanced by changes in soil temperature, moisture, and bulk density. This research emphasized the necessity to explore eco-friendly cropland practices in maize cultivation zones, which would contribute to the sustainable development of the agricultural sector with positive effects on reducing soil CO2 emissions and increasing crop yields. However, stability and validity need further investigation on long-term scales.