The effects of straw and calcium-rich materials on soil phosphorus availability in greenhouse tomato cultivation under continuous cropping

Soil phosphorus (P) availability is crucial for phosphorus uptake and yield formation in vegetables. Although long-term intensive farming can lead to soil phosphorus accumulation, phosphorus use efficiency is usually reduced. This study investigated the effects of long-term straw return to the field (R), application of calcium oxide (Ca), and a combination of both (RCa) on soil phosphorus composition and phosphorus cycling microbial communities in a continuous greenhouse tomato cultivation system through a long-term field experiment. The results showed that R and RCa significantly increased the content of active phosphorus components and decreased the content of moderately active phosphorus, while Ca treatment had little effect on phosphorus activation. RDA indicated that SOC and pH were the main factors regulating phosphorus composition. Compared with the control (CK), the R treatment significantly altered the composition of the phoD- and pqqC-containing microbial communities, while RCa significantly altered the phoD-containing microbial community composition. Structural equation modeling further reveals that soil pH directly affects the distribution of phosphorus components, while SOC indirectly promotes the accumulation of reactive phosphorus by stimulating the phoD microbial community. Therefore, under the conditions of this experiment, straw return to the field (R and RCa) mainly improves soil phosphorus availability by increasing soil organic carbon content and regulating phosphorus cycling microorganisms, thereby accelerating the conversion of moderately active phosphorus to active phosphorus. These findings provide a theoretical basis for improving phosphorus availability and promoting phosphorus cycling in greenhouse soils by returning straw to the field.