Effects of Long-Term Material Amendments on Soil Phosphorus Fractions and Associated Microbial Changes in Greenhouse Tomato Cultivation

Background and Aims: High phosphate fertilizer application is commonly used in facility vegetable cultivation to sustain high yields, but it leads to intense phosphorus fixation. While organic-inorganic amendments for soil remediation have been explored, their long-term effects on phosphorus availability and microbial mechanisms in continuous cropping soils remain unclear. Methods: This study, based on a long-term experiment, assesses the impact of mixed amendments (straw, biochar, and calcium oxide) on soil chemistry, phosphorus fractions, enzyme activities, and microbial communities (phoD and pqqC) in greenhouse continuous cropping systems, compared to a control (CK). Results: BCa and BRCa significantly increased soil pH. BR and BRCa treatments raised soil organic matter by 48% and 97%. All treatments boosted available phosphorus, total phosphorus, and microbial biomass phosphorus by 3.6–24%, 9.0–21%, and 24–49%. Labile phosphorus content increased, while medium labile and residual phosphorus decreased. BRCa treatment notably enhanced the richness of both phoD and pqqC communities. Conclusions: Combined application of straw, biochar, and calcium oxide improves soil properties and microbial communities, enhancing phosphorus availability.