Mixed Triticum aestivum and Vicia sativa cover crops and biofertilizers improve growth of continuous cropping Apium graveolens by altering soil chemistry and rhizosphere bacterial communities

Abstract

For sustainable agriculture, combined cover crops, bacterial fertilizers, and vermicompost are theoretically more beneficial, yet effects and mechanisms remain unknown. We conducted a pot experiment using Apium graveolens, susceptible to continuous cropping obstacles, as the main crop, with Triticum aestivum and Vicia sativa as mixed cover crops. Eight treatments were designed: CF (0.232 g chemical fertilizer·kg⁻¹ soil), BF (0.464 g bacterial fertilizer·kg⁻¹ soil), VMC (46.416 g vermicompost·kg⁻¹ soil), BV (0.232 g bacterial fertilizer·kg⁻¹ soil + 23.208 g vermicompost·kg⁻¹ soil), and CC/CB/CV/CBV (cover crops + CF/BF/VMC/BV, respectively). Growth, quality, soil chemical properties and rhizosphere bacterial were analyzed. CB and CV were most beneficial for growth and quality, respectively, both showing higher absolute abundances of total bacteria and Bacillus spp. CV increased α-diversity. Cover crops enriching network core OTU8551 (Bacillus spp.), and combinations with biofertilizers enriching OTU499 (Pseudomonas spp.). Vermicompost and cover crops increased network complexity, while cover crops partially restored the robustness reduction caused by biofertilizers. RDA analysis showed that cover crop–biofertilizer combinations were positively correlated with pH and negatively with EC. Mantel test indicated that network complexity was driven by EC, pH, NH₄⁺-N, NO₃⁻-N, and AP, while robustness was affected by EC, SOM, TN, NH₄⁺-N, NO₃⁻-N, and AP. In summary, combining cover crops with a single biofertilizer further boosts productivity. Bacterial fertilizers acted via individuals, while cover crops and vermicompost additionally enhanced bacterial interactions, all regulated by soil chemistry and contributing to beneficial rhizosphere effects.