Desorption and dissolution often control the mobility and availability of phosphorus (P) in the natural environment. In this study, P desorption was compared from a soil receiving either long-term inorganic or biosolid fertilization as a part of a long-term field scale research project. A continuous-flow desorption method was used to measure cumulative P desorption over time, and P K-edge X-ray absorption near edge structure spectroscopy was used to determine the chemical species removed from the soil samples by desorption. The cumulative amount of P released in the inorganic fertilizer–amended soil was higher (895 vs. 573 mg kg−1), and the rate of P release was much faster (k = 0.012 vs. 0.005 m−1) than that of the biosolids-amended soil. The kinetics data were best described by the parabolic diffusion equation (r 2 = 0.98–0.99), suggesting that P desorption was mass-transfer limited or that intraparticle diffusion could be the rate-limiting step. The X-ray absorption near edge structure results indicated that dissolution of calcium and iron phosphate minerals occurs in addition to desorption of P from the exchangeable sites. These observations suggest that the redistribution between aqueous, adsorbed, and precipitated phosphate (PO4 3−) species occurs rapidly when solution P concentrations are depleted.
1Department of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
2Water Reclamation District of Greater Chicago, Chicago, Illinois, USA.
Address for correspondence: Dr. Derek Peak, Department of Soil Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5A8. E-mail: email@example.com
Received August 9, 2011.
Accepted for publication November 1, 2011.
Financial Disclosures/Conflicts of Interest: This research was funded by National Science and Engineering Research Council (NSERC) Discovery Grant awarded to Derek Peak. This work is based in part on research conducted at the Synchrotron Radiation Center, University of Wisconsin-Madison, which is supported by the National Science Foundation under Award No. DMR-0537588. Research described in this article was also performed at the Canadian Light Source, which is supported by the Natural Sciences and Engineering Research Council of Canada, the National Research Council Canada, the Canadian Institutes of Health Research, the Province of Saskatchewan, Western Economic Diversification Canada, and the University of Saskatchewan.