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Fluid Journal : Winter 2014
12 The Fluid Journal Winter 2014 Table 1. P XANES data--Brazil Acid Soil Soil P species (%) Section 1: 0-7 .5 mm Treatment Aluminum Alumina Ferrihydrite Strengite Vivianite Red. Chi Phosphate Adsorbed Adsorbed Square P P Control 13.9 64.1 21.9 0.27 MAP 72.1 27.9 0.32 DAP 47.3 52.7 0.04 APP 43.6 56.4 0.02 Table 2. P XANES data--Idaho Calcareous Soil Soil P species (%) Section 1: 0-7 .5 mm Treatment Apatite Hydroxy Aluminum Ferrihydrite Vivianite Red. Chi apatite Phosphate Adsorbed P Square Control 20.4 48.2 31.4 0.06 MAP 59.2 31.0 9.8 0.02 DAP 64.1 35.9 0.04 APP 27.8 48.2 24.0 0.04 Figure 6: APP had significantly more resin extractable P as a percentage of total P as compared to the other two treatments. The first two sections of the petri dish for all treatments had significantly higher resin extractable P compared to the control and the last two sections. like Fe-P (21.9%) and aluminum phosphate- like Al-P (13.9%) in the Brazil control soil (Table 1). In contrast, no Al-P was observed in P-treated soils (center sections). All P treatments resulted in the disappearance of aluminum phosphate and an increase in the amount of aluminum adsorbed P, ferrihydrite adsorbed P, or vivianite. The changes may be due to both the increased soluble P levels and increase in pH produced by the fertilizers. The MAP treatment shows predominantly ferrihydrite adsorbed P and vivianite-like P. DAP and APP contained alumina adsorbed P, which may be a less soluble P form; however, overall adsorbed-P concentration in DAP and APP treatments was significantly less than the MAP-treated soils. There were no significant differences in resin extractable P between the APP and DAP-treated Brazil soils, although both had significantly higher resin extractable P than the MAP. The XANES analysis of the control Idaho soil (Table 2) indicated the presence of hydroxyapatite-like P (48.2%), ferrihydrite- adsorbed P (31.4%) and apatite-like P (20.4%). These P minerals would not be uncommon in a high pH calcareous soil. MAP and DAP had a higher percentage of apatite-like P forms close to the fertilizer application point as compared to the APP treated soils. These fertilizer treatments had the highest pH at the center section of their respective plates as well. APP had significantly less apatite-like P (Ca-P) and more Fe-P either as adsorbed or precipitated. Comparison of resin-extractable P data with XANES speciation results showed a negative correlation of Ca-P species with resin-extractable P, suggesting that Fe-P species in calcareous soils might be more available. Summing up The two soils used in this study had extreme pH, one being very acidic and the other alkaline. With the addition of granular or fluid P fertilizers, the pH values were modified to a level more favorable to higher P solubility. With increasing distance from the P application point, the soil pH either slowly increased or decreased toward its native pH. There was evidence of fertilizer P diffusion to the second section with the Brazil soil and up to the third section with the Idaho soil. We have no evidence that there were differences in P diffusion away from the point of application between the three P sources for either soil. The percent resin P results for Brazil soil indicated there was no statistical difference between the three sources. Results for the Idaho soil were different from the Brazil soil. There was significantly greater percent resin P in the center section with the APP (fluid fertilizer treatment) as compared with either MAP or DAP. MAP had significantly greater resin extractable P than DAP. The speciation results indicated that the addition of P induced the formation of P solid phases, including adsorbed as well as secondary P minerals. In calcareous soil, low pH and formation of less Ca-P species in the APP-treated soils may have been the reason for observed high resin extractable P concentrations. Further study is needed under field conditions to see if the soil chemical changes can influence plant growth. Ms. Joy Pierzynski is a Graduate Research Assistant working on her Ph.D, and Dr. Ganga Hettiarachchi is an Associate Professor, and Mr. Raju Khatiwada is a former graduate student in soil chemistry in the Department of Agronomy at Kansas State University.