Influences of a vermicompost application on the phosphorus transformation and microbial activity in a paddy soil

A pot experiment was conducted to investigate the effects of a vermicompost (VC) application on the phosphorus (P) transformation and microbial activity in a paddy soil. Changes in the following P forms were investigated: resin-P, concentrated HCl extracted inorganic (C.HCl-Pi) and organic P (C.HCl-Po), diluted HCl extracted inorganic P (D.HCl-Pi), NaHCO3 extracted inorganic (NaHCO3-Pi) and organic P (NaHCO3-Po), NaOH extracted inorganic (NaOH-Pi) and organic P (NaOH-Po), and residual P. The results showed that the vermicompost application significantly (P < 0.05) affected the pH, redox potential (Eh), water soluble Fe(II), HCl-extractable Fe(II), microbial biomass carbon (MBC), microbial biomass P (MBP), MBC/MBP ratio, and acid phosphatase activity (APA) of the paddy soil. In particular, the HCl-extractable Fe(II) increased by 25-56% with the vermicompost application when compared to the control (CK). With the exception of C.HCl-Pi, the vermicompost application greatly increased the contents of the various P forms in the soil. In particular, the labile P (resin-P, NaHCO3-Pi, and NaHCO3-Po) and moderately stable P (NaOH-Pi and NaOH-Po) were significantly (P < 0.01) increased. The correlation analyses showed that NaHCO3-Pi was significantly and positively related to the MBC, MBP, and APA, while NaHCO3-Po was significantly and negatively related to the MBC, MBP, and APA. Both NaOH-Pi and C.HCl-Pi were significantly and negatively related to the APA. Both NaOH-Po and C.HCl-Po were significantly and positively related to the MBP, while NaOH-Pi was significantly and negatively related to the MBP. These results indicated that a vermicompost application could effectively enhance the dissolution and reduction of Fe and the consequent mobilisation of NaOH-Pi. In addition, the vermicompost application significantly (P < 0.01) increased the APA and effectively mobilised the NaOH-Po.