This study analyzes the biotransformation of earthworms on K in potassium-bearing mineral powder (PBMP) under different PBMP recruitments. A mixture of PBMP (10% to 60% mass fraction) and decaying cow dung was used as feed for breeding the earthworms to study the potassium-releasing ability of earthworms on PBMP in soil. The mixture containing 20% and 30% PBMP resulted in good growth and propagation of the earthworms as well as higher conversion rates of potassium. Therefore, the optimum recruitments of mineral powder are 20% and 30%. The mixture of cow dung and PBMP was compared with the mixture of cow dung and corresponding proportions of quartz powder to analyze the conversion rate of earthworms on PBMP in different combinations. After the earthworms were raised with the mixture of cow dung and PBMP (8: 2 and 7: 3) for 30 d, the contents of rapidly available K and effective K were 10 824.3±35.9 and 11 688.4±16.1 mg·kg−1 as well as 10 079.6±62.2 and 10 247.5±172.7 mg·kg−1, respectively. After the earthworms were raised with the mixture of cow dung and quartz powder (8: 2 and 7: 3) for 30 d, the contents of rapidly available K and effective K were 10 623.3± 41.1 and 11 385.5±13.5 mg·kg−1 as well as 9 834.2±51.8 and 9 907.6±11.4 mg·kg−1, respectively. Thus, the contents of rapidly available K and effective K in the mixture of cow dung and PBMP were significantly higher compared with those in the mixture of cow dung and quartz powder (P<0.05). The increment contents of rapidly available K and effective K were 201.0 and 302.9 mg·kg−1 as well as 245.4 and 339.9 mg·kg−1, respectively. Therefore, earthworms can activate and trans-form K into effective K through feeding, digestion, absorption, and excretion. The results provided a new idea of using earthworms to release potassium in low-grade potassium-bearing rocks and obtain the rapidly available K and effective K needed by plants.
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