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ABSTRACT
Techniques used in making an experimental measurement of a step-by-step uptake of nutrients by plants are reported. Metal pans, divided in half, were filled with soil and covered by a collodion membrane. By fitting the halves of the pan together, plants were grown between the two membranes without actual soil-root contact. This technique made possible the growing of plant roots in a soil-free condition and enabled the measurement of the suites of cations at each of the following stages of nutrient uptake, (a) the non-adsorbed stage, (b) the adsorbed stage, (c) the absorbed stage in which the cations were absorbed into the roots, and (d) the suite of cations that were translocated to the above ground portions of the plant. Aliquots of electrodialyzed Sharkey and Ruston soils saturated to give 65% Ca and 3% K saturation of the exchange complex, and either 3, 6, 12, or 18% Mg saturation were prepared. Soybean plants were grown for a period of 4 weeks at which time the living plants were removed and the measurement of nutrient uptake at each of the various stages was carried out.
Increasing the percentage of Mg in either soil resulted in an increase in the percentage of Mg and a corresponding decrease in the percentage of Ca and K in the suite of cations at each stage of nutrient uptake. Ca dominated the suite of adsorbed cations on plant roots grown in the Ruston soil, while K dominated the suite of adsorbed cations on plant roots grown in the Sharkey soil. The Sharkey soil produced plants with Ca percentages of less than one-fourth of those grown on the Ruston soil despite the fact that with equal percentages of Ca saturation (65%) the Sharkey clay offered about 10 times the quantity of exchangeable Ca to the plant roots. A Mg saturation of 9% of the Ruston soil produced plants with equal Mg contents (0.30%) as did the Sharkey clay with 3% Mg saturation. The exchange properties of the plant root and the metabolic effects of the plant favored a greater movement of K than Mg or Ca from the root surface into the roots and tops of plants.
1 Research paper No. 1130 Journal Series, University of Arkansas, Fayetteville, Arkansas. Published with the permission of the Director of the Arkansas Agr. Exp. Sta. Presented before Div. II, Soil Science Society of America, Dallas, Tex., Nov. 18, 1953. This investigation was largely supported by a grant from the International Minerals & Chemical Corp.
2 Associate Professor of Agronomy and Junior Agronomist, respectively.
Received for publication January 8, 1954.
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