Effects of combined application of soybean fermentation broth with phosphate fertilizer on maize seedling growth and soil phosphorus availability

Objective To address the problem of low phosphorus (P) fertilizer utilization efficiency in crops caused by low P availability in acidic soils of southern China, this study used a pot experiment to investigate the effects of applying soybean fermentation broth combined with P fertilizer on soil available P.

Method Under the maize pot experiment, the content levels of KH₂PO₄ were set at 0.05, 0.10, and 0.15 g·kg⁻¹ respectively. For each level, four gradients (with dilution ratios of 100, 300, 500, and 700-time, respectively) of soybean fermentation broth were arranged for mixed application with KH₂PO₄.

Result The combined application of soybean fermentation broth and P fertilizer promoted maize growth at the seedling stage, mainly manifested in plant height, stem diameter, net photosynthetic rate, and root growth. Specifically, soybean fermentation broth mixing 0.05 g·kg⁻¹ P significantly promoted the balanced growth of maize plants and roots, with the leaf net photosynthetic rate being significantly increased by 75.03% compared with the P fertilizer alone treatment. In soil chemical properties, soybean fermentation broth mixing 0.05 g·kg⁻¹ P increased soil pH and effectively reduced soil electrical conductivity. At this P level, compared with the P fertilizer alone treatment, 100-time soybean fermentation broth resulted in a substantial increase of 258.86% in available P content. Meanwhile, the contents of Al-P and Fe-P showed the highest increases of 162.48% and 135.91%, respectively.

Conclusion The combined application of soybean fermentation broth and P fertilizer exerts a positive effect on soil P availability, with the 0.05 g·kg⁻¹ P level combined with 100-time soybean fermentation broth exhibiting a more pronounced enhancement effect on P availability.