Objectives Increasing the efficiency of phosphorus fertilizer utilization is a challenge that requires urgent attention in agricultural production. Here, we researched the role and mechanism of soil microorganisms in the morphological transformation of phosphorus fertilizer and utilization efficiency. We aimed to provide a basis for understanding the matching mechanism between crop-phosphate fertilizer types and soil microorganisms.

Methods Cinnamon low-phosphorus soil (Olsen-Pi =4.53 mg/kg) was used for a pot experiment with maize (Zhengdan 958). The experimental soil was treated with high-temperature sterilization and non-sterilization. Further, monoammonium phosphate (MAP), calcium magnesium phosphate (CMP), and ammonium polyphosphate (APP) fertilizers were applied to the soil at an equal nutrient supply of P 100 mg/kg. Also, a control (CK) without phosphorus fertilizer was set up. After maize harvest, soil pH, Olsen-Pi, alkaline phosphatase activity, dry shoot weight, phosphorus content were measured, and calculation of fertilizer rate was carried out. For each index, the difference between phosphorus fertilizer application and control was termed fertilizer effect, and the difference between unsterilized and sterilized was designated as the microorganism effect.

Results The fertilizer use efficiency in sterilized conditions was MAP>APP>CMP, with a significant difference among the treatments. There was no significant difference (P>0.05) in the fertilizer use efficiency of MAP and APP under unsterilized conditions, and the two treatments recorded higher values than CMP. Plant phosphorus content and rhizosphere Olsen-Pi in CMP treated unsterilized soil increased by 116.3% and 128.0% , compared with the sterilized soil. Similarly, fertilizer utilization rate, aboveground dry weight, plant phosphorus content, and rhizosphere Olsen-Pi in APP treated unsterilized soil increased by 40.7%, 34.2%, 41.2% and 38.2%, compared with the sterilized soil. The rhizosphere ΔpH of unsterilized soil treated with CMP was significantly lower than in sterilized soil. In contrast, compared with CK, the increment of alkaline phosphatase (ALP) activity in unsterilized soil treated with APP was significantly higher than that in sterilized soil.

Conclusions We find that the effects of soil microorganisms on different phosphorus fertilizers varies based on the application rate (100 mg/kg) adopted in this study. Soil microorganisms promote the mobilization of citric-acid soluble phosphate fertilizer (CMP) and polymerized phosphate fertilizer (APP). Water-soluble phosphate fertilizer (MAP) can meet plants phosphorus demand. Therefore, soil microorganisms do not play a key role in mobilizing MAP. An improved understanding of soil-phosphate fertilizer matching technology provides theoretical support to develop microbial regulation techniques for phosphate fertilizer application.