Effects of zeolite and microbial inoculants on vegetables and soil under continuous cropping in protected cultivation

Background and Aims: Continuous cropping obstacles threaten the sustainability of protected vegetable production by degrading soil structure, disrupting microbial communities, and reducing yield and quality. Zeolite amendment and functional microbial agents are promising countermeasures, but their combined effects in long-term continuously cropped soils have rarely been verified in the field. This study tested whether zeolite combined with microbial agents could synergistically improve soil quality and increase crop yield and quality. Methods A two-factor field experiment was conducted at three long-term (> 10 years) continuous cropping sites in Hebei Province, China: Kuancheng (tomato, Solanum lycopersicum L. cv. Yanyu), Luanping (tomato, S. lycopersicum L. cv. Xiaohongfan), and Chongli (colored pepper, Capsicum annuum L. cv. Meihong No. 1). Zeolite was applied at 0 and 3 t hm⁻² (F0, F1) in factorial combination with three microbial agent treatments (J0, no agent; J1, Bacillus amyloliquefaciens ; J2, Bacillus subtilis + Trichoderma harzianum ). Results Combined application increased yield by 33.5%–41.3% over the control (F0J0), increased soluble sugar, vitamin C, and soluble solids contents, and decreased titratable acidity. It also reduced bulk density by 8.7%–11.5% and EC by 33.7%–56.7%, increased bacterial and actinomycete counts by 152.4%–360.8% and 105.9%–176.6%, respectively, and raised the bacterial-to-fungal (B/F) ratio by 146.3%–326.6%. Conclusion Zeolite at 3 t hm⁻² combined with Bacillus subtilis and Trichoderma harzianum (F1J2) performed best at all sites. By improving soil properties and restoring microbial community structure, this combination alleviates continuous cropping obstacles and offers a practical option for protected vegetable production.