The present study aims to assess the influences of long-term crop straw returning and recommended potassium fertilization on the dynamic change in rice and oilseed rape yield, soil properties, bacterial and fungal alpha diversity, and community composition in a rice–oilseed rape system. A long-term (2011–2020) field experiment was carried out in a selected paddy soil farmland in Jianghan Plain, central China. There were four treatments with three replications: NP, NPK, NPS, and NPKS, where nitrogen (N), phosphate (P), potassium (K), and (S) denote N fertilizer, P fertilizer, K fertilizer, and crop straw, respectively. Results showed that long-term K fertilization and crop straw returning could increase the crop yield at varying degrees for ten years. Compared with the NP treatment, the long-term crop straw incorporation with K fertilizer (NPKS treatment) was found to have the best effect, and the yield rates increased by 23.0% and 20.5% for rice and oilseed rape, respectively. The application of NPK fertilizer for ten years decreased the bacterial and fungal alpha diversity and the relative abundance of dominant bacterial and fungal taxa, whereas continuous straw incorporation had a contradictory effect. NPKS treatment significantly increased the relative abundance of some copiotrophic bacteria (Firmicutes, Gemmatimonadetes, and Proteobacteria) and fungi (Ascomycota). Available K, soil organic matter, dissolved organic carbon, and easily oxidized organic carbon were closely related to alterations in the composition of the dominant bacterial community; easily oxidized organic carbon, dissolved organic carbon, and slowly available K were significantly correlated with the fungal community. We conclude that long-term crop straw returning to the field accompanied with K fertilizer should be employed in rice-growing regions to achieve not only higher crop yield but also the increase in soil active organic carbon and available K content and the improvement of the biological quality of farmland.

Soil microbes play an integral role in agricultural production and soil fertility, while limited information is available about the effects of long‐term fertilization on rice (Oryza sativa L.)–rapeseed (Brassica napus L.) rotation yield, soil properties, and microbial communities in central China. Here, we report the response of plant–soil system to different mineral fertilizer inputs, including the balanced fertilization with N, P, and K (NPK) fertilizers and unbalanced fertilizers without one of the major nutrients (PK, NK, and NP) for 10 years. Compared with the NPK treatment, the average annual decrease rates of rice and rapeseed yield in the PK, NK, and NP treatments were 12.5%, 18.1%, 6.4% and 33.1%, 54.8%, 16.0%, respectively. Long‐term fertilization significantly changed the soil chemical properties, especially the pH and available K content. Compared with the NPK fertilization, the NK treatment increased the soil microbial composition and diversity, whereas PK and NP treatments had a reverse impact. Available K, pH, and slowly available K were closely related to alterations of the dominant bacterial community. On the contrary, the Olsen‐P, slowly available K, and pH were significantly correlated with the fungal community. Soil properties changed by fertilization had a more direct effect on crop yield than the microbial community; moreover, the bacterial group had a higher influence than the fungal group on crop yield. Therefore, a balanced nutrient input using NPK fertilization is an effective management strategy for soil biological fertility and sustainable crop yield.