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Fluid Journal : Winter 2014
11 The Fluid Journal Winter 2014 Percent P added. For the Brazil soil (Figure 3), much of the P remained in the first two sections of the petri plates for all treatments. Most P remained close to the point of application and there were no significant differences between treatments in the 0-7.5 section. Phosphorus did diffuse into the second section (7.5-13.75 mm) for all 3 treatments. However, there were no significant differences between treatments in that section, either. High P fixation with aluminum and iron oxides and hydroxides, or forming solid phases with iron and/or aluminum, most likely prevented P movement into the outer two sections of the dish. For the Idaho soil (Figure 4), the majority of the P remained in the center section of the petri dishes for all three treatments with no significant difference between them. MAP appeared to have greater diffusion into the second section than other treatments, though it was not significantly different from any other treatment. Percent Resin P. Resin extractable P analysis is used as an estimate of plant available P in soils. Anion exchange membranes mimic P uptake by roots and is considered to be an acceptable method to assess labile P in the soil. Total soil P analysis is a measure of the many P forms that exist in soil samples. Calculation of percent resin P allows for normalization of the data when comparing treatments because of slight variations in the amount of P added to each dish and the possibility that the treatments can influence the diffusion distance for added P. High percent resin P means a greater proportion of the P in the soil is potentially available for plant uptake. For Brazil soil (Figure 5), the center petri dish section for all three treatments had the highest extractable P though there were no significant differences between treatments. The second, third, and fourth dish sections contained significantly less resin extractable P for all treatments, with a small increase in the third and fourth sections of the dish. Percent resin P results on the Idaho soil were more complex (Figure 6). The APP treatment had the greatest percent resin P in the center section when compared to either granular fertilizer treatment. It was clear that when P was applied as APP to Idaho calcareous soil, although it did not appear to enhance P movement further into other sections, APP helped to remain in potentially plant-available forms. DAP had significantly less labile P in calcareous soil than the MAP treatment. Moreover, there was a significant enhancement of resin extractable P levels in the 7.5 -13.75 mm section for all treatments compared to the control treatment. The third and fourth sections had percent resin P values equivalent to the control treatment. XANES analysis. Phosphorus was present as ferrihydrite-adsorbed P (64.1%), vivianite- Figure 3: There were no significant differences between the treatments. Nearly all the fertilizer P added remained within the first two sections of the petri dish for all three P treatments. Figure 4: Though there were no significant differences between the three treatments APP had more actual fertilizer P in the first section compared to the other two treatments. Similarly, although there was enhanced fertilizer MAP movement in the second section it was not significant. Figure 5: Though there were no significant differences between the three treatments, APP had more resin extractable P as a percentage of total P in the first section than the other two treatments. The first two sec- tions of all P treated soils had significantly more resin extractable P compared to the control and the two remaining sections.