Effect of tillage system on soil CO2 flux, soil microbial community and maize (Zea mays L.) yield

•Studied tillage effects on soil CO2 flux, microbial community and maize yield under different precipitation.•Long-term no-tillage (NT) affected maize yield not soil annual CO2 emission.•NT combated July drought by improving soil moisture and microbial biomass.•NT is a positive adaptation strategy to cope with drought in NE China. Selecting appropriate soil management practices (e.g. tillage treatments) provides an opportunity to sequester soil carbon (C), improve soil health, and achieve ample food production in an agricultural system. The responses of soil CO2 emission, soil microbial community, and crop yield to precipitation are crucial for assessing sustainability of conservation tillage. Soil CO2 flux, soil microbial phospholipid fatty acid (PLFA) contents and crop yield were measured in a long-term (15 years) tillage study in the Northeast of China under a normal year in 2013 and natural drought year in 2015. The results showed in a normal year with precipitation similar to the 30-year mean, soil temperatures at 5, 10 and 20 cm in June under mouldboard plough (MP) were higher by 0.9, 1.0 and 1.1 °C, respectively, than under no-tillage (NT); soil water content in the top 22 cm under MP was significantly lower than that under NT in 04 June and 31 July; and MP significantly increased maize (Zea mays L.) yield and C emission efficiency (the ratio of yield to annual soil CO2 emission) by 22% and 25%, respectively. In a dry year (2015), soil temperatures at 5, 10, and 20 cm in June and July under MP were higher by 2.0, 1.8 and 1.7 °C than under NT, respectively; soil water content in the top 22 cm under MP was significantly lower than under NT by 28% in July; moreover, MP significantly decreased maize yield and C emission efficiency by 47% and 63%, respectively. However, there were no significant differences in annual soil CO2 emission between NT and MP in the normal and dry years. Compared with MP, NT significantly increased soil microbial PLFA contents in pre-planting (April) and late segments of the growing season (August-September) of a normal year, but significantly increased soil microbial PLFAs content in pre-planting and all of early, mid and late segments of the growing season in a dry year. Structural equation modelling (SEM) revealed that soil water content, temperature, bacteria and fungi directly contributed to C emission efficiency. Tillage was indirectly associated with C emission efficiency through soil water content, temperature, soil fun