Bianhong Zhang

Silicon deficiency is widespread in soils of Southeastern China and may constrain nitrogen (N)-use efficiency and yield formation in oilseed rape; therefore, this study aimed to identify an N-reduction window enabled by silicon (Si) fertilization and to clarify the underlying mechanisms. Field experiments were conducted in Putian, Fujian Province (2023–2025), with five treatments: conventional N (T1, 300 kg·N·ha⁻¹), conventional N plus Si (T1+Si, 150 kg·Si·ha⁻¹), and three N rates (120%, 80%, and 60% of conventional N; T2+Si, T3+Si, and T4+Si) under a fixed Si input. Yield, N-use efficiency, plant physiological traits, soil quality index (SQI), and nitrogen-cycle ecosystem multifunctionality were assessed. Compared with T1, T1+Si and T3+Si increased yield by 6.55% and 6.06%, respectively, accompanied by higher dry matter translocation (27.20% and 34.60%) and improved N-use efficiency (28.86% and 39.66%). SQI increased by 31.42% (T1+Si) and 33.03% (T3+Si), while nitrogen-cycle multifunctionality increased by 32.42% and 58.42%, respectively. Correlation and path analyses indicated that Si promoted yield formation by simultaneously alleviating soil constraints (lower exchangeable acidity and Al³⁺; higher cation exchange capacity) and enhancing plant assimilation and allocation processes, thereby reducing potential N losses and strengthening N cycling. Overall, applying 150 kg·Si·ha⁻¹ combined with a 20% reduction in N (240 kg·N·ha⁻¹) achieved stable yield gains and coordinated improvements in soil quality, providing an operational fertilization window for Si-enabled N management in regional oilseed rape systems.

Chili pepper (Capsicum annuum L.) is a globally significant economic crop, however long-term continuous cropping often induces multifaceted constraints including soil nutrient depletion, rhizosphere microbial imbalance, and pathogen accumulation, which collectively exacerbate soil-borne diseases and substantially reduce yield. Incorporating rice (Oryza sativa L.) into rotation increases the diversity of the cultivation environment and represents a cost-effective strategy to mitigate continuous-cropping obstacles. Therefore, evaluating and elucidating the role and underlying mechanisms of the chili pepper–rice rotation system in improving soil conditions and alleviating continuous cropping obstacles in chili pepper holds significant importance. This study conducted a two-year field experiment from 2023 to 2024, setting up chili pepper–rice rotation (RVR) and chili continuous cropping (CCV) treatments, to systematically analyze the effects of chili pepper–rice rotation on chili pepper yield, disease occurrence, soil nutrients, and rhizosphere microbial communities. Across 2023–2024, RVR significantly reduced the incidence of bacterial wilt and root rot, increasing yield by 10.60% in 2023 and by 61.07% in 2024 relative to CCV. Analysis of soil physicochemical properties revealed that RVR significantly promoted the accumulation of available nitrogen, phosphorus, and potassium in the soil, as well as enhanced nutrient-acquisition enzyme activity, effectively alleviating the carbon and phosphorus limitations faced by rhizosphere microorganisms. Rhizosphere microbial analysis indicated that under the RVR treatment, the abundance of pathogen-associated taxa such as Ralstonia and Fusarium significantly decreased. The co-occurrence network modularity increased, and the negative cohesion of pathogens was strengthened, thereby inhibiting pathogen expansion. Further random forest and correlation analyses demonstrated that RVR significantly contributed to yield formation by optimizing fungal metabolic pathways, such as galactose degradation, sulfate reduction, and L-tryptophan degradation. In conclusion, the chili pepper–rice rotation significantly alleviates continuous cropping obstacles and enhances yield by improving nutrient supply and regulating microbial community composition, as well as the topological structure and functional relationships of their co-occurrence networks, particularly by strengthening the role of fungi in community function and metabolic regulation. This study provides a theoretical basis for the biological and soil regulation of pepper continuous cropping obstacles and offers a feasible pathway for sustainable cultivation and green control strategies.