Combining conservation tillage with nitrogen fertilization promotes maize straw decomposition by regulating soil microbial community and enzyme activities

Straw return can effectively improve the farmland soil microenvironment and soil fertility. However, excessive straw in the topsoil adversely affects seed germination and crop growth. At present, the characteristics and key driving factors of straw decomposition in dry farmlands are unclear. Based on the interaction between three tillage practices (i.e., zero-till (ZT) and chisel-till (CPT) vs. conventional plow-till (PT)) and three nitrogen fertilizer rates (i.e., low nitrogen (N1: 180 kg N ha-1) and high nitrogen (N3: 300 kg N ha-1) vs. normal nitrogen (N2: 240 kg N ha-1)), quantitative polymerase chain reaction (qPCR) technology and an enzymatic detection kit were used to investigate the effects of key straw-decomposition enzyme activities and microbial abundance on straw decomposition during the growth period of winter wheat. Between 2018 and 2020, repeated in situ measurements of straw decomposition indicated that zero-till and chisel-till significantly increased winter wheat yield (ZT: 10.94%; CPT: 12.79%) and straw decomposition velocity (ZT: 20%; CPT: 26.67%), compared with plow-till. N2 (240 kg N ha-1) significantly increased wheat yield (N1: 4.65%; N3: 5.31%) and straw decomposition velocity (N1: 26.33%; N3: 13.21%), compared to N1 (180 kg N ha-1) and N3 (300 kg N ha-1), respectively. The partial least squares pathway model showed significant positive direct effects of soil moisture, NO3-, NH4+, total nitrogen, bacteria, cellulase, laccase and xylanase activities on straw decomposition, while pH, fungi and Actinomycetes had significant negative direct effects on straw decomposition. Overall, conservation tillage (zero-till and chisel-till) combined with N2 (240 kg N ha-1) is beneficial for straw decomposition in the drylands of the Loess Plateau and improve straw resource utilization and basic soil fertility. The results of the study clarify the key drivers of straw decomposition in dryland farmlands, and provide new ideas for developing updated soil management practices and adaptive nitrogen application strategies to promote the resource utilization of straw and achieve the goals of carbon peaking and carbon neutrality.