Cassava–Maize Rotation Improves Soil Quality and Microbial Gene Profiles Compared to Continuous Cassava Cropping

Due to limited land resources and traditional farming practices, continuous cassava cropping is common in China. This practice leads to soil degradation, including reduced fertility, imbalanced microbial communities, and lower crop yields. In this study, we investigated the impacts of continuous cassava cropping (CC) and cassava–maize rotation (RC) systems on soil physicochemical properties, microbial community composition, and functional gene abundance related to carbon and nitrogen cycling. The RC system consists of a five-year rotation cycle: cassava is planted in the first year, followed by two consecutive years of maize, and then, cassava is planted again in the last two years. The soil type is classified as Haplic Acrisols with a clay loam texture in this research. Soil samples from both cropping systems were analyzed for physicochemical properties and enzyme activities, and the results showed significant decreases in soil pH, available nitrogen, available phosphorus, and available potassium in CC. Using metagenomic sequencing, 1,280,928 and 1,224,958 unigenes were identified under RC and CC, respectively, with differences in microbial taxonomic and functional profiles. Bacteria accounted for 89.257% of the soil community in RC, whereas the proportion was 88.72% in CC. The proportions of eukaryota and viruses in RC were 0.031% and 0.006%, respectively; in contrast, their proportions were 0.04% and 0.02% in CC, respectively. Cassava–maize rotation promoted the metabolic activities of soil microbes, leading to a significant enhancement in functional genes related to nitrogen and carbon cycling, such as nasA, nasD, nrtC, coxA, porA, and frdA. This shows that microbial activity and nutrient cycling improved in the crop rotation system. Thus, these findings highlight the importance of crop rotation for maintaining soil health, enhancing microbial functions, and improving sustainable cassava production. This study provides valuable insights into the management of cassava agroecosystems and the mitigation of the adverse effects of continuous cropping.