Objectives We compared the beneficial effects of straw return modes on cinnamon soil chemical and biological fertility, to lay a basis for efficient culturing of fertile farmland.

Methods The research was based on a 30-year long trial from 1992−2022, located in Shouyang, Shanxi Province. The experiment was composed of four maize straw return methods: not returned to field (CK), mulching on the field (SM), crushed and ploughed directly into field (SC), and returned to field after used as forage (CM). Soil nutrient content, enzyme activity, and bacterial community structure were comprehensively analyzed using high-throughput sequencing technology, FAPROTAX functional prediction, and ecological network methods.

Results 1) Long-term straw return (SM, SC and CM) significantly increased soil nutrient contents and extracellular enzyme activities. Compared with CK, the soil organic carbon, total N, total P, total K, alkali-dissolved N, available P, quickly available K contents were elevated in ranges of 17.0%−42.9%, 3.0%−50.0%, 2.3%−27.9%, 4.4%−11.5%, 11.2%−71.0%, 14.1%−320.8%, 17.1%−153.6%, soil glucosidase (β-GC), cellobiose hydrolase (CBH) and dehydrogenase (DHA) contents were elevated in ranges of 35.6%−190.7%, 41.9%−58.6%, and 28.8%−773.8%, cumulative maize yields increased by 6.4%−23.0%, respectively. 2) SM, SC and CM treatments increased soil bacterial Chao 1 index, Peilou’s evenness index and Shannon’s index, the relative abundance of Bacteroidetes, Proteobacteria, Firmicutes, and Actinobacteria, and decreased the relative abundance of Chloroflexi and Acidobacteria. Soil pH and organic carbon were important factors influencing bacterial community composition. 3) The results of the network analysis showed that the indicator species of the straw return treatments belonged to different modules and were significantly correlated with soil nutrient content and enzyme activities. The Chryseolinea, enriched in the CM treatment, had formed specific functional microbial clusters through strong symbiotic relationships. 4) Functional prediction based on FAPROTAX found that long-term straw return increased the potential of organic matter decomposition and nitrogen conversion of soil flora.

Conclusions Long-term different straw return significantly enhanced soil fertility and maize yield, increased soil enzyme activity, significantly increased bacterial diversity, changed the structure and composition of bacterial communities, and improved the function of soil carbon and nitrogen cycling, thus promoting the formation of a suitable environment for crop and bacterial growth in cinnamon soil.