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Evidence for Different Reaction Pathways for Liquid and Granular Micronutrients in a Calcareous Soil

^a Soil and Land Systems, School of Earth and Environmental Sciences, Univ. of Adelaide, Waite Campus, Glen Osmond, SA 5064, Australia
^b CSIRO Land and Water, PMB 2, Glen Osmond, SA 5064, Australia
^c National Risk Management Research Lab., U.S. Environmental Protection Agency, 5995 Center Hill Ave., Cincinnati, OH 45224
^d GSECARS, Univ. of Chicago, Chicago, IL 60637

View larger version (114K): [in this window] [in a new window]   Fig. 1. Backscattered electron micrographs of cross-sections of granular Mn (a) unexposed and (b) incubated for 5 wk in soil, and granular Zn (c) unexposed and (d) incubated for 5 wk in soil.

View larger version (79K): [in this window] [in a new window]   Fig. 2. Micro-x-ray fluorescence maps of Mn, Ca, Fe, and K or Zn for soil incubated with (a) granular Mn and (b) granular Zn. Area of a single map is 10,000 by 500 µm for granular Mn added to soil and 8000 by 5000 µm for granular Zn added to soil. The color scheme used ranges from white or yellow for high-fluorescence signal to blue or black for low-fluorescence signal. Shading is relative across each map. The markers noted as P1 to P5 and P36 to P39 represent locations for which µ-x-ray absorption near-edge structure (XANES) analyses were conducted. The XANES spectra are presented in Fig. 6 and 8 and the XANES fitting is presented in Tables 3 and 5.

View larger version (108K): [in this window] [in a new window]   Fig. 3. Micro-x-ray fluorescence maps of Mn, Zn, Fe, and Ca for the soil incubated with fluid Mn and Zn. Area of a single map is 10,000 by 5000 µm. The color scheme used ranges from white or yellow for high-fluorescence signal to blue or black for low-fluorescence signal. Shading is relative across each map. The markers noted as P7 to P11 and P 13 to P16 represent locations for which µ-x-ray absorption near-edge structure (XANES) analyses were conducted. The XANES spectra are presented in Fig. 6 and 8 and the XANES fitting is presented in Tables 3 and 5.

View larger version (18K): [in this window] [in a new window]   Fig. 4. The radial distribution plots for Mn and Zn generated using micro-x-ray fluorescence (µ-XRF) maps for soils treated with granular Mn, granular Zn, and liquid Mn and Zn plus technical-grade monoammonium phosphate (TGMAP+MnZn).

View larger version (22K): [in this window] [in a new window]   Fig. 5. Bulk Mn x-ray absorption near-edge structure (XANES) spectra of selected Mn standards, soils, and incubated granular Mn in soil (TGMAP is technical-grade monoammonium phosphate). Dotted lines indicate the linear combination XANES fits using all the standard compounds. Vertical dashed lines represent white line peaks for Mn2+ and Mn4+, respectively. Soil Section 1 is the soil up to 4 mm from the point of fertilizer application, and Section 2 is the soil between 4 and 7.5 mm from the point of fertilizer application. Granular Mn Section 2 was similar to untreated soil and therefore not included.

View larger version (21K): [in this window] [in a new window]   Fig. 6. Manganese micro-x-ray absorption near-edge structure (XANES) spectra of selected different Mn hotspots shown in Fig. 3 (granular) and 4 (liquid) for soil treated with granular and liquid Mn. Dotted lines indicate the linear combination XANES fits using all the standard compounds. Vertical dashed lines represent white line peaks for Mn2+ and Mn4+, respectively.

View larger version (22K): [in this window] [in a new window]   Fig. 7. The raw Zn k3–weighted (where k is the photoelectron wavenumber) extended x-ray absorption fine structure (EXAFS) spectra (solid lines) for the Zn K-edge bulk x-ray absorption spectroscopic data. Dotted lines indicate the linear combination fits using all the standard compounds.

View larger version (13K): [in this window] [in a new window]   Fig. 8. Zinc micro-x-ray absorption near-edge structure (XANES) spectra of selected point of interest (hotspots) in soil treated with liquid Zn (technical-grade monoammonium phosphate + Mn and Zn) or granular Zn (monoammonium phosphate + Zn). Dotted lines indicate the linear combination fittings.