RELATIONSHIPS OF EXCHANGEABLE AND NON-EXCHANGEABLE POTASSIUM IN SOILS ADJACENT TO CATION-EXCHANGE RESINS AND PLANT ROOTS

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Abstract
In a determination of the depletion of exchangeable K in the soil adjacent to the roots of corn seedlings and the possible mechanism of the replenishment of the exchangeable K, columns of soil (2 cm long) were partially depleted of exchangeable K by placing hydrogen-saturated cation-exchange resin in contact with one end. The results indicate about 20% of the total K taken up by the resin was derived from non-exchangeable form. After removal of the resin very little release of non-exchangeable K occurred. Replenishment of exchangeable K in the portion of the column originally adjacent to the resin was primarily by diffusion from non-depleted portions of the column. Adjacent to the 2- and 3-day-old portions of the root, the exchangeable K in the soil was depleted to a measurable extent; adjacent to the 4- and 5-day-old portion of the root, uptake appeared to be limited and the diffusion of K replenished the depletion of the 1st 3 days. Growth and development of lateral roots by days 6 and 7 was sufficient to markedly deplete the soil adjacent to the root of exchangeable K. These observations were correlated with the stage of development of the root tissues.

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