Kaliumdynamik im wurzelnahen Boden in Beziehung zur Kaliumaufnahme von Maispflanzen

Potassium dynamics at the soil-root interface in relation to the uptake of potassium by maize plants Young maize plants were grown in flat containers on a sandy and a silt loam soil after addition of ⁴³K as tracer. Changes of the K concentration in soil in the vicinity of the roots were determined by scanning the film density of autoradiographs. A distinct zone of K depletion in the soil adjacent to the root surface was observed, similar to those found earlier with phosphate and rubidium. The highest degree of depletion occured within a distance of 0.7 mm from the surface of the root cylinder which corresponds to the average length of root hairs of the cultivar used. The quantity of K released within 2.5 days per unit of this part of the soil exceeded the exchangeable K by a factor of two. In a radial direction the zone of maximum depletion was followed by a depletion profile which extended over 5 mm in the sandy and over 3 mm in the silt loam soil. The K concentration of the soil solution decreased to 2–3 μmoles K/l at the root surface. In order to determine the effect of depleting the K concentration by plant roots on the release of soil K, desorption studies were carried out in parallel. For this purpose the soil was successively extracted by solutions with cation concentrations corresponding to the soil solution, except for K. With this procedure a massive release of K from the soil was observed after the equilibrium concentration decreased to 2–3 μmoles K/l. It is concluded that

• – in one growing season only part of the soil volume of the rooted layer contributes potassium to the plant and, on the other hand
• – substantial part of the potassium absorbed by plants is derived from nonexchangeable soil K, even in short periods of time.