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Fluid Journal : Fluid Journal 2002-2004
Early Spring 2004 Fluids Beat Granular in Soil Trials Drs. M. McLaughlin, E. Lombi, B. Holloway, R. Armstrong, Ms. C. Johnston, Ms. D. Brace Summary: Data indicate that fluid fertilizers are superior to granular for delivery of phosphorus (P) for crop nutrition in calcareous soils. Field and glasshouse experiments have demonstrated in southern Australian soils the benefits of fluid formulations for crop nutrition. Experiments were performed using similar fertilizer products delivered either in fluid or granular form to calcareous soils. Isotopic and spectroscopic techniques were used to characterize reactions. Granular fertilizers were found to be inferior to fluids (even with the same formulations) due to the precipitation of insoluble Ca/Al phosphates similar to crandallite in the fertilization zone (i.e., in and around the granule). As determined by isotopic dilution studies, P diffusion from the incorporation zone was inhibited with granular applications and the ability of P in the fertilized zone was also reduced when P was applied in granular form. Fixation of applied P is minimized when fertilizers are supplied in fluid form. Some formulations may have the added advantage of liberating fixed P in the soil-to-plant available forms. lkaline soils, abundant throughout the world, constitute a major soil type for agricultural use in South Australia (SA). For example, calcareous soils in SA (5 to 90% CaCO3) cover an arable area greater than 2.5 million acres and produce 40 percent of SA's wheat crop. Previous work has indicated that fluid fertilizers are highly efficient in Granular fertilizers found to be inferior to fluids in calcareous soils. Fluid Journal 1 A calcareous soils of SA and Victoria, two of the most southern states in Australia. Large areas of both these states are characterized by low annual rainfall (between 9 and 14 inches) and calcareous and alkaline soils account for large percentages of the annual cereal production area. This study was focused specifically on the reactions of granular and fluid products in these soils, using isotopic dilution and spectroscopic techniques to identify reaction products and to characterize the solubility of these nutrient sources and their availability to plants. Improveddiffusion Results from this study show that granular MAP (one of the two most common fertilizers used in SA cereal production) is an extremely inefficient source of P in highly calcareous soils, due to poor dissolution of the granule. Petri dish. Examination of total P concentrations on the various zones around the granule or fertilized zone indicated a very different distribution of P in the zones, depending on whether MAP was supplied in granular or liquid form (Figure 1). When MAP was supplied in granular form, much more of the P in the petri dish system was concentrated in the first zone around the granule itself (Section 1). Supply of MAP in the fluid form (TGMAP) allowed much more of the P to diffuse away from the fertilized zone (Section 1) into outer sections of soil (Sections 2 and 3). In fact, over 80 percent of the P supplied as granular MAP is still within 0.25 inches from the center of the petri dish. In contrast, when P was applied TGMAP, over 40 percent of the total P applied was found between 0.25 and 0.5 inches from the center of the petri dish (Figure 1).
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