Abstract
PAPR was made by partial acidulation of North Carolina phosphate rock with H3PO4. The PAPRs were incubated in bands in columns of two soils of contrasting P retention. The columns were sampled after freezing and sectioning with a cryomicrotome. The movement of P in soil incubated with33P-labelled PAPR was followed by autoradiography of polished epoxy impregnated sections of the freeze-dried soil column. PAPR solubility was also studied by a sequential dialysis process using distilled deionised water. The acid solution resulting from the dissolution of monocalcium phosphate (MCP) in PAPR moved into the surrounding soil, solubilizing soil minerals and creating a low-pH front with a high concentration of P. Depending on the soil, phosphorus moved 6–14 mm away from the fertilizer/soil interface by mass flow and diffusion in two days. The increase in 0.5 M NaOH extractable P above that of untreated soil showed a maximum at the same position as the pH minimum in the soil. In both soils, the total P movement from the fertilizer band after a two day period for 50% PAPR was comparable to that for 100% acidulation (≡triple superphosphate), indicating that acidulations above 50% did not necessarily increase the movement of soluble P from the fertilizer pellet. Variations in pH in the fertilizer-affected soil could be explained by the net balance of acidity resulting from incoming acid P solution and release of OH− during P sorption. The rock residue exhibited a transient loss in solubility which was reversed on subsequent dissolution, suggesting a possible surface alteration.
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Golden, D.C., White, R.E., Tillman, R.W. et al. Partially acidulated reactive phosphate rock (PAPR) fertilizer and its reactions in soil. Fertilizer Research 28, 281–293 (1991). https://doi.org/10.1007/BF01054329
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DOI: https://doi.org/10.1007/BF01054329