Humic acid becomes a source of phosphate and carbon, stimulating microflora populations. It also provide sites for microflora to colonize. The bacteria secrete enzymes which act as catalysts, liberating calcium and phosphorous from insoluble calcium phosphate, and iron and phosphorous from insoluble iron phosphate. As the calcium, phosphorous, and iron elements are liberated, they are absorbed by the humic acid present, making the elements less available to the bacteria.