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Fluid Journal : Fluid Journal 2005-2007
16 Fluid Journal FALL 2007 Energy (eV) 6530 6540 6550 6560 6570 6580 6590 6600 Intensity Untreated soil Granular Mn soil section 1 TG MAP+Mn soil section 1 H3PO4+Mn soil section 1 Birnessite (Mn IV) Mn carbonate (Mn II) Mn2+ Mn4+ (data not shown). Both XRD and SEM-EDAX analyses indicated that the concentration of Zn species in the incubated granules became higher following their incubation in soil possibly due to the decreased concentration of major nutrient elements (i.e., N and P). XRD analysis of incubated Zn granules showed that some ZnO was still present. Furthermore, both XRD and SEM- EDAX analysis suggested that a significant amount of Zn remaining in the incubated granules was present in mixed metal phosphate forms (i.e., Zn, Ca, and Al phosphates). The chemistry of Zn in fertilized soil appeared to vary little with the form of Zn fertilizer added. Analysis of both the micro and bulk x-ray absorption data indicated that for granular Zn, Zn phosphate-like and Ca/Zn phosphate-like compounds dominated the reaction products. For fluid Zn, adsorbed Zn or Zn silicate-like compounds appeared to dominate the Zn spectra (data not shown). Nriagu (1984)* suggested the formation of sparingly soluble mixed metal-Zn phosphates as a possible mechanism restricting Zn solubility in alkaline environments. Conclusions XRF mapping of soil/fertilizer reaction zones indicated that the mobility of Mn and Zn from fluid fertilizer was greater than observed for equivalent granular sources of these trace elements in a calcareous soil. X-ray microscopic and spectroscopic analyses agree with our previous isotopic dilution techniques and provide evidence that when fluid Mn and Zn were applied to soil, a considerably greater proportion of these micronutrients remained in relatively more soluble minerals compared Figure 3. Mn x-ray absorption spectra for different treatments and the line of best fit by combining various mixtures of spectra of pure Mn minerals. Dotted lines indicate where peaks are expected for the two oxidation states of Mn (Mn2+ and Mn4+). to the granular forms. Our data suggest that the superior agronomic effectiveness of fluid Mn and Zn fertilizer observed in calcareous soils under field conditions may have resulted from the enhanced diffusion and/or solubility of these micronutrients in soil when applied in fluid form. Moreover, this study confirms that the combination of different x-ray techniques, including synchrotron-based x-ray techniques, is useful for identifying reaction products of micronutrients in the soil. * Formation and stability of base metal phosphates in soils and sediments, p. 318-329. In J.O. Nriagu and B.P. Moore (Eds.) Phosphate Minerals. Springer-Verlag, Berlin. Dr. Hettiarachchi is research scientist, Dr. McLaughlin is senior principal scientist, Dr. Chittleborough is research associate, Dr. Lombi is senior research scientist, CSIRO, SA, Australia; Dr. Scheckel is research soil scientist, U.S. EPA, Cincinnati, OH; Dr. Newville is senior research associate, Argonne National Lab.
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