Legacy effects and residue returns: Soybean rotation surpasses maize and residue management in reshaping the rhizosphere for sugar beet productivity

Residue incorporation and preceding crop selection are considered critical agronomic strategies for sustainable agriculture, showing great potential for mitigating soil degradation and reducing the risk of continuous cropping in sugar beet cultivation. This study explores how four distinct cropping system treatments—sugar beet following soybean (SB), sugar beet following maize (MZ), continuous sugar beet without residue incorporation (SR−), and continuous sugar beet with residue incorporation (SR+)—reshape the sugar beet rhizosphere, with emphasis on plant performance, nutrient assimilation, soil chemistry, and microbial assemblages. The findings showed that the cropping system treatments significantly altered soil pH and nutrient status, which in turn reshaped bacterial and fungal communities regulating soil enzyme activities and ultimately influencing plant growth. Among the treatments, the SB treatment markedly enhanced sugar beet physiological performance, showing the highest root sugar content (13.23%), which was significantly greater than that of the MZ, SR+ , and SR− treatments (P < 0.05). The microbial co-occurrence network associated with SB was more complex and exhibited greater ecological resilience, comprising 517 nodes and 748 edges, and indicating higher ecological stability compared with SR+ and SR−. Partial least squares path modeling (PLS-PM) further demonstrated that the four cropping system treatments described above influenced sugar beet physiological traits primarily through a cascade of effects: modifying soil properties, reshaping microbial diversity, and subsequently enhancing soil enzyme activity. Overall, the SB treatment was identified as the most effective management strategy for optimizing microbial network structure and promoting sugar beet growth. These findings provide a theoretical basis for designing rational crop rotation systems and achieving sustainable sugar beet production. • Preceding crop management is the main factor shaping beet rhizosphere microbiomes. • Soybean as preceding crop improves yield, nutrients, and stabilizes networks. • Maize preceding crop ranks second; residue return aids short-term; no residue worst. • Cropping treatments regulate plant growth via soil, microbes, and enzyme activity.