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This article in SSSAJ

  1. Vol. 22 No. 2, p. 124-129
    Received: Oct 3, 1957
    Accepted: Dec 5, 1957

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The Effect of Associated Salts on the Availability of Concentrated Superphosphate1

  1. D. R. Bouldin and
  2. E. C. Sample2



Phosphorus uptake by oat plants grown in the greenhouse on 2 soils fertilized with pellets of concentrated superphosphate (CSP) alone or of mixtures of CSP and each of 5 salts was measured. With Hartsells fine sandy loam (pH 5.2) yields of P were in the order: CSP < CSP + KCl ≤ CSP + NH4Cl ≤ CSP + NH4NO3 < CSP + (NH4)2SO4 ≤ CSP + KNO3. With Mountview silt loam (pH 6.6) yields of P were in the order: CSP < CSP + KCl < CSP + (NH4)2SO4 ≤ CSP + NH4Cl ≤ CSP + NH4NO3 ≤ CSP + KNO3.

After pellets of CSP, CSP + KNO3, and CSP + NH4NO3 had reacted with the moist soils for 3 weeks, samples of soil were taken at increments of distance from the center of the pellet residue. Both water-soluble P (1:15 soil-water extracts) and P extractable in 6N HCl were linear functions of distance of the sample from the center of the pellet residue. The constants in the linear equations depended upon the composition of the pellet. The summation, over the total volume of soil influenced by fertilizer, of the products of water-soluble P × volume of soil containing this concentration of water-soluble P was well correlated with the uptake of P by oats in the greenhouse experiment. Thus, the effect of the associated salts on the availability of the CSP was largely explained on the basis of measured chemical differences. Any effects on physiology of the plants were of secondary importance in this experiment.

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