Effective Volume of Soil Around Plant Roots Determined from Phosphorus Diffusion

Abstract

AbstractThe 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.