Phosphorus adsorption in some Australian soils and influence of bacteria on the desorption of phosphorus

Seven Australian soil samples were collected from different locations (Camden, Griffith, Narrabri, Rutherglen, Wagga Wagga, Wee Waa (Ivanhoe), and Yanco) to measure their phosphorus (P) adsorption rates. Soils were collected from the top 0-15cm, and P was added at 0, 100, 200, 300, 400, and 500 mu g P g(-1) soil. Results indicated that P adsorption increased significantly with increasing levels of added P. In subsequent studies, soils from Griffith and Narrabri and two bacteria Pantoea spp. known as FA001 and FA010 were tested for P mobilization at 100 mu g P g(-1) soil concentration. The rate of P mobilization [P extracted by 0.01M calcium chloride (CaCl2)] in the Narrabri soil showed significant differences between treatments, but with and without bacteria, this was not the case for the Griffith soil. In Narrabri soil, the highest extractable P (0.492 mu g g(-1)) was obtained with the treatment containing the strain FA001 after bacterial lysis with trichloromethane (CHCl3), and the lowest P (0.236 mu g g(-1)) was measured in the treatment without bacterial amendment and without CHCl3 treatment, indicating the P-mobilizing ability of the strain FA001. It was found that the minimum P-adsorption capacities (revealed from the Langmuir and Temkin adsorption isotherms) of the Narrabri and the Griffith soils are 357 and 500 mu g g(-1), respectively; the buffering capacities of the Narrabri and the Griffith soil are 71.7 and 93.7 mu g g(-1), respectively. These findings indicate that soils with high P adsorption and buffering capacities are less likely to respond to the P-mobilizing bacteria. Therefore, the application of the Langmuir and Temkin adsorption isotherms for estimating soil P-adsorption and buffering capacities can be used to predict the potential usefulness of biofertilizer application.