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Fluid Journal : Winter 2014
10 The Fluid Journal Winter 2014 Percent P added was calculated by dividing the net increase in total P mass in each ring by the total P mass added to each petri dish, multiplied by 100. The net increase in total P mass is the total P concentration in a ring minus the native or control total P concentration, multiplied by the soil mass in that ring. Percent Resin P was calculated as resin extractable P concentration divided by the total P concentration, multiplied by 100. In addition, scanning electron microscopy- energy dispersive x-ray analysis was performed on residual granules of DAP and MAP after the incubation, and P K-edge x-ray absorption near-edge structure spectroscopy (XANES) analysis of bulk soil of the 0.75 mm section for each treatment was performed to determine fertilizer reaction products. Statistical analyses. All data were analyzed using the Proc GLM procedure using SAS software (SAS 9.2, 2008). The Bonferroni Pairwise Method was used for comparison of all treatments at a 0.05 level of significance. Synchrotron-based bulk x-ray adsorption near-edge structure (XANES) spectroscopy analysis was performed at sector 9 BM-B, Advanced Photon Source, Argonne, IL to determine the chemical form of P reaction products. Spectra for the various standard compounds and soil samples were edge- energy calibrated, background corrected and normalized. The reduced XANES spectra for the samples were analyzed by linear combination fitting (LCF) using IFEFFIT software (Newville, 2001). Study overview pH. For the Brazil soil, all treatments that received P had significantly higher pH as compared to the control treatment in the first three sections of the petri dish, with no difference at 35-43.5 mm from the point of P application (Figure 1). In general, the pH was highest at the point of P application and decreased to background levels by the fourth section. The pH increases were due to the dissolution of P fertilizer followed by chemisorption of dissolved P onto iron/ aluminum oxides followed by release of hydroxyl ion and/or from the hydrolysis of urea added with MAP and APP treatments (for DAP urea was not added). Given the acidic nature of the native soil, further acidification due to the ammonium-N may not have occurred due to inhibition of the nitrification process. For the Idaho soil, all treatments were significantly lower in pH as compared to the control treatment in all four sections of the petri dish (Figure 2). The pH, more acidic at the point of P application, increased out to the fourth section and most likely was the effect of acidification due to nitrification. The APP treatment had the lowest pH although it was not statistically significant from the MAP treatment in some sections. Figure 1. Soil pH- Brazil Acid Soil Figure 2. Soil pH- Idaho Calcareous Soil