Identification and quantitation of P compounds and its transformation products in a dual P band using X-ray absorption near edge spectroscopy (XANES)

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The long-term objective of this study is to significantly increase the efficiency of fertilizer phosphorus uptake by the crop. In the short term, our objectives are i) to identify and quantify the phosphorus compounds and sulphate salts that are formed in dual bands of P fertilizer using X-ray absorption near edge structure (XANES) spectroscopy; ii) to follow the transformation of these initial P compounds in time using XANES and iii) to determine those salt combinations that will increase P solubility and thereby P availability to plants. Low phosphate fertilizer efficiency in high pH soils is primarily due to the slowing down of P movement in the soil-P fertilizer reaction zone. This is caused by rapid reaction of the applied P with soil components such as exchangeable Ca2+ and Mg2+ displaced into soil solution. Measures that have been taken to rectify this problem include the modification of the chemical environment of soil-P fertilizer reaction zone through the co-application of non-phosphatic salts with fertilizer P. In a recently completed study, we demonstrated that the application of sulphate or carbonate salts of ammonium with either monoammonium phosphate or monopotassium phosphate increased the solubility and chemical diffusion of phosphorus (Akinremi et al. 2006). This enhancement was attributed to anionic competition between sulphate or carbonate and P for the displaced exchangeable or solubilized calcium. We hypothesized that the formation of CaSO4 reduced the precipitation of P thereby increasing solution P. However, the chemical form of the precipitated P is unknown and there is no direct evidence for the presence CaSO4 in the soil. The proposed study will demonstrate the application of "state of the art" spectroscopic technique to finding practical solution of low phophorus fertilizer use efficiency. Our ability to identify and quantify the P minerals that are formed in a dual band will aid our efforts at finding the right formula for improving the fertilizer use efficiency of P by the crop. An increase in phosphorus fertilizer use efficiency will provide economic and environmental benefits for Canadian farmers through reduced input cost and reduced residual soil phosphorus.