The effects of continuous reduction of phosphorus fertilizer application on soil phosphorus components and phosphorus-solubilizing microorganisms were studied, and the transformation law of soil phosphorus was explored to provide a theoretical basis for rational application of phosphorus fertilizer and efficient utilization of phosphorus in soil.

In 2014, the phosphorus reduction positioning test was carried out in Longmen Town, Mianyang, Sichuan province. The test set 4 treatments, namely P0 (no phosphorus fertilizer), P1 (1/2 reduction, 45 kg·hm^-2), P2 (1/3 reduction, 60 kg·hm^-2), and P3 (normal fertilization, 90 kg·hm^-2), and 0-20 cm soil samples were collected to measure and analyze soil total phosphorus (TP), available phosphorus (AP), and phosphorus activation coefficient (PAC), phosphorus fractions and the change characteristics of phosphorus-dissolving microorganisms.

Reducing the application of phosphorus fertilizer significantly reduced the TP content of the soil; compared with 2014, after 3 years of continuous treatment, the TP content under P0 and P1 treatments decreased by 7.2% and 0.9%, respectively, however, which under P2 and P3 treatments increased by 2.6% and 7.3%, respectively; after 6 years of continuous treatment, the TP difference between treatments was further expanded: compared with 6 years ago, the TP under P0 and P1 treatments decreased by 15.2% and 5.7%, respectively, which under the P2 and P3 treatments increased by 7.8% and 21.6%, respectively. The variation trend of AP content was similar to that of TP. After continuous treatment for 3 years, the content of AP under P0 treatment decreased by 18.1%, while that under P1, P2, and P3 treatments increased by 21.2%, 72.2%, and 132.1%, respectively; compared with 6 years ago, the AP variation of each treatment expanded to -24.6%-201.6% after continuous treatment for 6 years. The PAC was determined by the content of AP and TP, and its variation trend was generally consistent with that of AP. Reducing the application of phosphorus fertilizer mainly caused a significant decrease in the content of H₂O-P, NaHCO₃-Pi and NaOH-Pi, but had no significant effect on Residual-P. Among them, NaOH-Pi was the main phosphorus form that caused the change of soil TP content, and NaHCO₃-Pi was the most critical phosphorus fraction in the process of soil phosphorus activation. There were differences in the abundance of phosphorus-solubilizing microorganisms in different phosphorus fertilizer treatments. Redundancy analysis results showed that Nocardioides, Mycobacterium, Bacillus, Hyphomicrobium and Rhizobium were positively correlated with each form of phosphorus, among which, the genus Hyphthora was highly correlated with NaHCO₃-Pi and NaOH-Pi.

The reduction of phosphorus fertilizer significantly changed the composition of soil phosphorus pool, and the changes of soil AP and TP were mainly affected by the changes of NaHCO₃-Pi and NaOH-Pi. There were significant differences in the abundance of soil phosphorus-dissolving microorganisms after 6 years of continuous reduction of phosphorus fertilizer, and the genus Hyphomicrobium was the key microorganism involved in the transformation of phosphorus in the experimental area. Reducing the application of 1/3 phosphorus fertilizer for 6 consecutive years could effectively reduce the accumulation of slow-release phosphorus in the soil in this experimental area while maintaining a high level of available phosphorus.