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This article in SSSAJ

  1. Vol. 68 No. 2, p. 682-689
    Received: May 22, 2003

    * Corresponding author(s): enzo.lombi@csiro.au


Mobility and Lability of Phosphorus from Granular and Fluid Monoammonium Phosphate Differs in a Calcareous Soil

  1. E. Lombi *a,
  2. M. J. McLaughlina,
  3. C. Johnstona,
  4. R. D. Armstrongb and
  5. R. E. Hollowayc
  1. a CSIRO Land and Water, PMB 2 Glen Osmond, SA 5064, Australia
    b Agriculture Victoria, Victorian Institute for Dryland Agriculture, Natimuk Rd, PB 260, Horsham, VIC 3400, Australia
    c South Australian Research and Development Institute, Minnipa Agricultural Centre, PO Box 31, Minnipa SA 5654, Australia


Phosphorus availability is a major factor limiting crop production in highly calcareous soils. Recent field trials on calcareous soils in southern Australia have shown that fluid fertilizers may provide a useful alternative to granular fertilizer products. Fluid sources of P enhance P uptake and yield when compared with granular fertilizers applied at the same rate. This work aimed to compare the behavior of one fluid (technical grade monoammonium phosphate, TG-MAP) and one granular (monoammonium phosphate, MAP) form of P fertilizer in a highly calcareous soil. Changes in soil pH, P diffusion, solubility, and lability (using isotopic dilution techniques) were determined at different distances from the point of application over 5 wk. Furthermore, reaction products in MAP granules were investigated using spectroscopic techniques. The results indicated that P from fluid TG-MAP diffused more and was more available than P supplied as granular MAP. Also, X-ray diffraction (XRD) and energy dispersive X-ray microanalyses (EDXMA) of the MAP granules indicated that a significant percentage (12%) of the initial P remained in the granules even after 5 wk of incubation in the soil. The enhanced P availability of fluid fertilizers observed in field trials compared with granular forms is discussed in relation to differences in the dissolution, diffusion, and reaction processes in soils.

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