Conclusions

• Manures containing greater concentrations of soluble P produced correspondingly greater increases in soluble P following incorporation into the soils.
  
  
• Microbial activity and the amount of carbon added appear to exert a greater influence on the P solubility of incorporated manures than their chemical composition.
  
  
• C:P ratios in manures may be important in determining P solubility when incorporated into soils. Future studies should aim to determine how carbon additions affect soil P chemistry, and how microbial activity regulates P availability .