This paper examined the effect of the addition of two sources of readily available phosphate, triple superphosphate and microbiologically solubilized phosphate, and of a not readily available source, Araxá apatite, on maize crop. In addition, the effects of inoculation of Aspergillus niger, a fungus that solubilizes rock phosphate, and of the addition of organic matter were examined. When organic matter was used, the total microbial population increased, but no effect was observed on phosphorus production or uptake by the maize crop. Both the triple superphosphate and Araxá apatite enhanced the production of dry matter and phosphorus uptake by maize as compared to the control (no phosphorus) and to microbiologically solubilized phosphate. Also, inoculation of A. niger had no effect on rock phosphate solubilization, possibly due to the interference of the natural microorganisms of the soil. The number of microorganisms and acid phosphatase activity were lower in the soil fertilized with triple superphosphate than in the soil fertilized with rock phosphate.
rock phosphate solubilization; Aspergillus niger; maize