Commercial phytases are widely used in poultry production, but little is known about their potential use as biofertilizer for agricultural crops as an alternative to reduce the use of synthetic fertilizers. Four purified phytases isolated from Aspergillus niger and Escherichia coli were characterized biochemically and in terms of their adsorption to soils belonging to the Mollisol order. Three different organic P substrates were used to measure enzyme activity under a wide range of pH (2.3 to 9) and temperatures (-10 to 70 ºC) conditions: phytic acid, p nitrophenyl-phosphate (pNP) and glyceraldehyde-3-phosphate (G3Phosphate). Phytases had a low affinity for the solid phase: 23 %-34% of the added amount was adsorbed after 1 h of incubation. Phytases from A. niger showed a higher capacity to release P (13% on average) than phytases from E. coli. All phytases were active throughout the pH and temperature ranges related to optimum crop production. At pH values commonly found in agricultural soils (5.5-7), A. niger phytases released P with the following substrate ranking with respect to effectiveness: pNP greater than phytic acid greater than G3Phosphate. E. coli phytases, in comparison, released P following with the following substrate ranking with respect to effectiveness: pNP = phytic acid greater than G3Phosphate. The results obtained are promising in terms of the use of phytases as a complement to P fertilization in agricultural settings and encourage further studies under field conditions.