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This article in SSSAJ

  1. Vol. 30 No. 5, p. 598-602
    Received: Mar 4, 1966
    Accepted: July 1, 1966

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Effective Volume of Soil Around Plant Roots Determined from Phosphorus Diffusion1

  1. S. R. Olsen and
  2. F. S. Watanabe2



The effective volume of soil contributing P to the roots was measured from a knowledge of the diffusion coefficient of P, a capacity factor for renewal of the soil solution, and the P concentration in solution. Rate of P uptake per square centimeter of surface area by excised corn roots was measured from P32-tagged soils at ⅓-bar moisture suction. The rates of release of resin-extractable P from the soils were determined. These rates of release of extractable P from the effective volume of soil were much greater than the rate of uptake by the roots. The data indicate strongly that the rate of release of solid phase soil P to the soil solution is a nonlimiting step in the absorption mechanism of P by roots.

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