Field experiments were conducted from 2023 to 2024 at the Shatian sorghum experimental planting plot in Shanshui Village, Luban Street, Renhuai City, Zunyi City, Guizhou Province (E106°17′, N27°42′). The experimental site is characterized by a subtropical humid monsoon climate, an average annual precipitation of 800–1,000 mm, a flat terrain, an altitude of 915 m, and typical yellow soil. Sorghum was continuously cropped at the experimental site from 2020 to 2023. A uniform planting pattern was adopted: sorghum was planted at a rate of two seeds per hole, with a row spacing of 50 cm, plant spacing of 25 cm, and planting density of 10,700 plants/hm². A single crop was cultivated per year, followed by a fallow period in autumn and winter. On September 28, 2023, before conducting the experiment, soil samples from the 0–20 cm soil layer were collected using the five-point sampling method to measure the following soil parameters: pH (6.68), soil organic matter (SOM, 38.2 g/kg), alkali-hydrolyzable nitrogen (223 mg/kg), available phosphorus (AP, 34.8 mg/kg), and available potassium (AK, 170 mg/kg).

In the experiment, which began in October 2023, three treatments—SSS (continuous cropping of sorghum for 5 years), SRS (sorghum–rapeseed–sorghum rotation after 4 years of continuous sorghum cropping), and SMS (sorghum–stem mustard–sorghum rotation after 4 years of continuous sorghum cropping)—each with three replicates (totaling nine plots, each with an area of 49 m²), were arranged in a randomized block design. Fertilization levels were consistent across plots. A 1.0-m isolation zone was established between different plots, and tillage was carried out separately for each plot. Sorghum and other autumn–winter cash crops were planted according to local standards.

Hongyingzi, Youyan 2020, and Yuzao 100 were the tested sorghum, rapeseed, and stem mustard varieties, respectively, in the experiment. Rapeseed was sown in the first 10 days of October 2023 and harvested in late April 2024. Stem mustard was sown in late October 2023 and harvested in mid-January 2024. Sorghum was sown in early May 2024 and harvested in early September 2024.

At the filling stage (August 12, 2024) of sorghum, three sorghum plants were randomly selected from each plot. Using a sterile sampling shovel, the soil-attached root system (diameter: 20 cm; depth: 30 cm) was excavated in a ring along the base of the sorghum stem. The root system was gently lifted and shaken to remove loosely attached soil, while the tightly adhering soil along the growth direction of the root system was brushed off using a sterile soft brush with a width of 2 cm. Mixed rhizosphere soil samples were prepared per plot. After debris, such as dead leaves, gravel, and residual roots, had been removed from the mixed samples using tweezers, the soil samples were passed through a 2-mm sieve. Afterwards, the soil samples were placed in self-sealing bags with labels, quickly frozen in dry ice, and immediately transported to the laboratory. Subsequently, the soil samples were divided into two portions: one portion was stored in an ultra-low temperature refrigerator at −80°C, while the other portion was air-dried for preservation after sieving.

Data were sorted and statistically analyzed using Excel. One-way analysis of variance were performed using SMSS 19.0.

The SOM, TP, TK, and alkali-hydrolyzable nitrogen content of the rhizosphere soil of sorghum in the SRS and SMS treatments were significantly higher than those of the rhizosphere soil of sorghum in the SSS treatment (p < 0.05; Table 2). Both SSS and SMS treatments significantly increased soil pH. Meanwhile, the concentrations of AP and AK in the rhizosphere soil of sorghum in the SRS treatment were significantly lower than those in the rhizosphere soil of sorghum in the SSS and SMS treatments (p < 0.05). Soil enzymes are important mediators in soil biochemical processes, playing a crucial role in maintaining soil ecological functions. Their activity reflects the ability of soil nutrient transformation and transport, serving as an important basis for evaluating comprehensive soil fertility (He et al., 2024). Among the treatments, URE and INV activities were highest in the SRS treatment; specifically, these significantly increased by 39 and 56%, respectively, compared with those in the SSS treatment (p < 0.05). Therefore, the fertility status of sorghum rhizosphere soil is significantly affected by different planting patterns.

Continuous cropping obstacles, also known as replant disease, refer to the phenomenon where long-term continuous cultivation of the same crop or its related species on the same land leads to changes in soil nutrient availability, allelopathy, and soil microorganisms, thereby affecting crop growth (Ma et al., 2023; Zeeshan Ul Haq et al., 2023) Long-term monocropping disrupts the soil ecological environment (Chen et al., 2020), induces pest infestations (Xi et al., 2019), and ultimately impairs crop growth and reduces yield, exerting a significant negative impact on agricultural development. Numerous studies have shown that crop rotation can improve soil physicochemical properties and, thus, promote crop growth. For example, maize–soybean rotation increases soil carbon and nitrogen storage, thereby improving soil quality (Luo et al., 2024), maize–tobacco rotation increases soil pH and cation exchange capacity (Jiang et al., 2025), and pea–potato rotation enhances SOM and TN content (Wang et al., 2023). In this study, we evaluated the effects of sorghum–rapeseed and sorghum–stem mustard rotations on the growth of Guizhou sorghum, and the results revealed that compared with traditional continuous sorghum cropping, the quality of the rhizosphere soil of sorghum significantly improved after sorghum–rapeseed and sorghum–stem mustard rotations, as evidenced by increases in soil pH and SOM, TP, TN, TK, and alkali-hydrolyzable nitrogen levels, because rapeseed and stem mustard increase soil nutrient content and the likelihood of colonization by various microorganisms through rhizodeposition and residue return (Zhou et al., 2024). Consequently, nitrogen, phosphorus, potassium, and other nutrients are released from the soil through mineralization and humification, providing a material basis for the continuous replenishment of the soil nutrient pool (Guggenberger, 2005). In this study, the AP and AK levels in the rhizosphere soil of sorghum in the SRS treatment were significantly lower than those in the rhizosphere soil of sorghum in the SSS and SMS treatments, probably because rapeseed is a phosphorus- and potassium-loving crop. Although its roots can activate insoluble phosphorus and potassium through chelation, given consistent fertilization levels, it still absorbs large amounts of phosphorus and potassium from the soil to maintain normal plant growth (Urricariet et al., 1995; Zhao et al., 2020). These traits of rapeseed provide support for the field management of sorghum–rapeseed rotation.

Soil URE and INV serve as key catalysts in nitrogen and carbon cycles between the soil and plants (Gu et al., 2009; Qin et al., 2022) investigated diversified tobacco rotation patterns and found that flue-cured tobacco rotation effectively increased soil URE and INV activities. Similarly, our results revealed that compared with the SSS treatment, URE and INV activities in the rhizosphere soil of sorghum significantly enhanced after the SRS treatment, probably due to the specific substances secreted by rapeseed roots, such as flavonoids and glucosinolates, that can effectively regulate and improve the structure and activity of soil microbial communities, thereby increasing soil enzyme activities. For example, glucosinolates attract nitrifying bacteria, which form symbiotic relationships with microorganisms that produce soil enzymes such as URE and phosphatase; hence, glucosinolates not only provide soil bacteria with a suitable growth environment but also indirectly enhance soil enzyme activities (Dong et al., 2018).

Diversified crop rotation systems increase the species richness and diversity of soil microorganisms, making a more complex and stable soil microbial community structure (Sun et al., 2024), which in turn regulates and improves the soil environment. The results of this study revealed that compared with the SSS treatment, the SRS and SMS treatments affected the abundance and diversity of rhizosphere soil microorganisms to varying degrees. The significant increase in the abundance of bacterial communities as well as the diversity of soil bacteria and fungi in sorghum rhizosphere soil in the SMS treatment may be attributed to the unique physiological characteristics of stem mustard roots and their exudates. As a succulent plant with high water content, stem mustard is more easily decomposed than fibrous plants. Under sufficient moisture conditions, more and diverse beneficial microorganisms quickly gather on the plant and decompose its nutrients. The SRS treatment also improved the diversity of bacteria and fungi in sorghum rhizosphere soil; however, unlike in previous studies, the ratio of bacteria to fungi decreased in the SRS treatment owing to the abundance of organic substances such as cellulose and lignin in rapeseed plants. After rapeseed harvest, residual root stubble and aboveground residues are returned to the soil, inducing changes in the abundance of soil bacteria and fungi. The results of this study are consistent with a previous finding that as the complexity of crops increases, beneficial fungi responsible for decomposing plant residues exhibit stronger adaptability while bacterial abundance decreases sharply (Miao et al., 2025).

The relative abundance of the dominant bacteria and fungi varied among the treatments. Notably, the SRS treatment effectively regulated the abundance of Ascomycota in the fungal community by significantly reducing its relative abundance. Studies have shown that some Ascomycota species are plant pathogens that cause root rot and affect plant growth (Challacombe et al., 2019). In contrast, the SRS treatment increased the relative abundances of Basidiomycota and Mortierellomycota, probably due to the interaction between rapeseed root exudates, such as sugars, proteins, and mucilage, and soil nutrients to provide abundant carbon sources and energy for beneficial fungi, attracting them to gather and reproduce around the roots. In addition, Basidiomycota and Mortierellomycota elicit antagonistic effects on some plant pathogens, inhibiting pathogen growth and competing for more nutrients for their own reproduction (Card et al., 2021).

Several researchers have reported that different soil factors affect the distribution of microbial structures. For example, Philippot et al. (2024) identified that soil pH, soil organic carbon, and oxygen partial pressure are key drivers of microbial community structure and activity, while Sadeghi et al. (2023) used the Cubist model to predict soil microbial communities based on soil properties and found that soil nutrients, such as nitrogen, phosphorus, potassium, and organic matter, are significantly correlated with the relative abundance of most soil microorganisms. The results of correlation and redundancy analyses in this study showed that INV activity, TP, TK, AK, and SOM are key factors affecting the structure of microbial communities in sorghum rhizosphere soil; specifically, these were significantly positively correlated with the relative abundances of Proteobacteria, Bacteroidota, Basidiomycota, and Nitrospirota. These findings indicate that sorghum rotation can significantly increase soil nutrient content and enzyme activity, thereby increasing the abundance of beneficial microbial communities and improving soil quality.

The optimization of soil properties further reshapes the rhizosphere microenvironment, and a favorable rhizosphere microenvironment can directly drive the structural succession and functions of microbial communities. Ultimately, the “root–shoot interaction” mechanism promotes the overall growth performance of sorghum, effectively alleviating the impact of continuous cropping, enhancing plant growth, and significantly increasing crop yield (Zhang et al., 2024). For example, Wu et al. (2025) demonstrated that highland barley–wheat or highland barley–rapeseed rotation improved soil quality, thereby increasing highland barley yield. Zhou et al. (2024) found that optimizing the rice–rapeseed rotation system significantly improved crop yield and yield stability, as rice and rapeseed yields increased as the duration of rotation prolonged. Yang X. et al. (2024) reported that diversified wheat rotation increased crop yield. Healthy roots usually secrete a large amount of organic and antibacterial substances into the soil, attracting various microorganisms to enrich the rhizosphere. These secretions serve as a bridge connecting plant roots and rhizosphere microorganisms, playing a key role in influencing the structure of the rhizosphere biological community (Haichar et al., 2008). The results of this study showed that compared with the SSS treatment, the SRS and SMS treatments significantly increased sorghum root activity. The optimization of soil properties further reshapes the rhizosphere microenvironment, creating favorable conditions for sorghum growth. This may be because long-term continuous cropping increases soil bulk density, reduces total soil porosity, leads to soil compaction, and restricts root growth (Hammel, 1989; Ajayi et al., 2021). Rotation with taproot crops, such as rapeseed and stem mustard, can effectively improve soil physical structure, enhance soil permeability and aggregate stability (He et al., 2024), and increase soil water retention through two-season cultivation (Schlegel et al., 2019), making the soil looser and promoting root development. Long-term continuous cropping easily leads to an imbalance in the soil microbial community structure, resulting in the proliferation of pathogens, reduction of beneficial bacteria, and accumulation of allelochemicals in crops (Ding et al., 2024; Gan et al., 2025), thereby inhibiting healthy root development. Root exudates, such as organic acids secreted by rapeseed roots, can activate insoluble phosphorus in the soil (Luo et al., 1999), and rapeseed rhizosphere soil is rich in potassium-solubilizing bacteria that dissolve insoluble potassium (Xiao et al., 2017). This nutrient enrichment effect can directly alleviate the problem of single soil nutrients due to continuous sorghum cropping, providing a more balanced nutrient environment for root development. After stem mustard straw is returned to the field, the decomposed organic matter and available nutrients accelerate the degradation of sorghum autotoxic substances in continuous cropping soil (Chen S. et al., 2022), reducing allelopathic inhibition and promoting root growth.

In our study, compared with the SSS treatment, the SRS and SMS treatments significantly improved the field agronomic traits of sorghum, such as plant height, stem diameter, and leaf area, and significantly increased sorghum yield. This finding is attributed to the enhanced sorghum root system in rotation treatments through improved nutrient supply and reduced allelopathic pressure (Chen Y. et al., 2022). Sorghum root exudates regulate the root microbial community structure, improve the efficiency of soil nutrient absorption and utilization (Xu et al., 2025), and promote aboveground growth through the root–shoot feedback mechanism (Liu X. et al., 2022). For example, at the jointing and panicle flowering stages, the leaf area of sorghum in the rapeseed rotation area increased by 48 and 19%, respectively, compared with that in the SSS treatment. The photosynthetic pigment content and photosynthetic rate of leaves may have significantly increased, improving the synthesis rate of photosynthetic products. Increased plant height and stem diameter resulting from the SRS and SMS treatments promote the transport of assimilates from leaves to sorghum panicle grains, making the grains fuller and ultimately improving grain quality and yield.

To optimize sorghum planting patterns, rotation demonstration bases should be established in major sorghum-producing areas in Guizhou (e.g., Renhuai and Zunyi), and farmers should be guided in adopting the two-year three-crop rotation patterns of sorghum–rapeseed and sorghum–stem mustard to replace traditional continuous cropping. To address the needs of the local Baijiu industry, the combination of brewing sorghum and characteristic cash crops should be promoted, and farmers’ income should be augmented through industrial chain extension (e.g., rapeseed processed into edible oil or stem mustard developed into pickled products). Moreover, clarify the connection time of rotation crop sequences (e.g., rapeseed is sown in October and harvested in April, while sorghum is sown in May), optimize fertilization and plant protection plans, reduce difficulty in farmers’ operation, and ensure the standardization and replicability of rotation patterns.

To improve the soil nutrient characteristics of rotation areas, implement the technology of soil testing and formula fertilization + organic fertilizer return to field, focus on supplementing phosphorus and potassium fertilizers, and improve soil carbon and nitrogen reserves by combining crop straw return to field to improve soil physical and chemical properties. Install long-term soil microorganism monitoring points in main producing areas to dynamically track the changes in microbial community structure (e.g., bacteria/fungi ratio, dominant microbial communities), providing data support for rotation effect evaluation. Furthermore, develop a soil health digital platform to achieve precise recommendations for rotation patterns and fertilization plans through farmers’ uploads of sample test results.

Encourage scientific research institutes to conduct research on root interaction mechanisms of rotation crops, analyze the regulatory effects of root exudates of different crops on soil pathogens, and explore more efficient rotation combinations (e.g., sorghum paired with leguminous crops) to provide theoretical support for optimizing planting structures. Guide Baijiu enterprises (e.g., Moutai and Xijiu) must sign rotation orders with farmers and enhance farmers’ enthusiasm through price incentives (e.g., premium purchasing). Include rotation in the cultivated land protection project, provide subsidies to farmers who implement rotation for a long time, and prioritize farmland infrastructure construction to ensure the sustainability of the farming system.