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

本研究的长期目标是显著提高作物对肥料磷的吸收效率。短期内，我们的目标是i)利用x射线吸收近边结构（XANES）光谱识别和量化磷肥双波段中形成的磷化合物和硫酸盐；ii)使用XANES及时跟踪这些初始P化合物的转化；iii)确定哪些盐组合将增加P的溶解度，从而提高P对植物的可利用性。在高pH土壤中，磷肥效率低主要是由于土壤-磷肥反应区磷素运动缓慢所致。这是由于施用的磷与置换到土壤溶液中的可交换Ca2+和Mg2+等土壤成分发生快速反应造成的。为纠正这一问题所采取的措施包括通过将非磷酸盐与磷肥共同施用来改变土壤-磷肥反应区的化学环境。在最近完成的一项研究中，我们证明，将硫酸铵或碳酸铵与磷酸一铵或磷酸一钾一起施用可增加磷的溶解度和化学扩散（Akinremi et al. 2006）。这种增强归因于硫酸盐或碳酸盐与磷之间的阴离子竞争，以取代可交换或可溶解的钙。我们假设CaSO4的形成减少了磷的沉淀，从而增加了溶液磷。然而，沉淀的磷的化学形式是未知的，没有直接证据表明土壤中存在CaSO4。该研究将展示“最先进”的光谱技术在寻找低磷肥利用效率的实际解决方案中的应用。我们识别和量化在双带中形成的磷矿物的能力将有助于我们找到正确的配方，以提高作物对磷的肥料利用效率。磷肥利用率的提高将通过降低投入成本和减少土壤残磷，为加拿大农民提供经济和环境效益。

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.