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

Abstract

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-P<sub>i</sub>) and organic P (C.HCl-P<sub>o</sub>), diluted HCl extracted inorganic P (D.HCl-P<sub>i</sub>), NaHCO<sub>3</sub> extracted inorganic (NaHCO<sub>3</sub>-P<sub>i</sub>) and organic P (NaHCO<sub>3</sub>-P<sub>o</sub>), NaOH extracted inorganic (NaOH-P<sub>i</sub>) and organic P (NaOH-P<sub>o</sub>), 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-P<sub>i</sub>, the vermicompost application greatly increased the contents of the various P forms in the soil. In particular, the labile P (resin-P, NaHCO<sub>3</sub>-P<sub>i</sub>, and NaHCO<sub>3</sub>-P<sub>o</sub>) and moderately stable P (NaOH-P<sub>i</sub> and NaOH-P<sub>o</sub>) were significantly (P < 0.01) increased. The correlation analyses showed that NaHCO<sub>3</sub>-P<sub>i</sub> was significantly and positively related to the MBC, MBP, and APA, while NaHCO<sub>3</sub>-P<sub>o</sub> was significantly and negatively related to the MBC, MBP, and APA. Both NaOH-P<sub>i</sub> and C.HCl-P<sub>i</sub> were significantly and negatively related to the APA. Both NaOH-P<sub>o</sub> and C.HCl-P<sub>o</sub> were significantly and positively related to the MBP, while NaOH-P<sub>i</sub> 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-P<sub>i</sub>. In addition, the vermicompost application significantly (P < 0.01) increased the APA and effectively mobilised the NaOH-P<sub>o</sub>.