A Sensitive Method for Detecting the Depletion of Nonexchangeable Potassium in the Rhizosphere Using a Sequential Extraction with 0.01 Molar Hydrochloric Acid

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To detect subtle depletion of nonexchangeable K occurring in the rhizosphere, extraction with a much weaker acid solution (0.01 M HCl) than that conventionally used (1 M HNO_3, 1 M HCl) was attempted. Soils sampled from the rhizoboxes in which maize (Zea mays L.) had been growing for 17 d was sequentially extracted, first with 1 M NH_4OAc to remove water-soluble and exchangeable K and then repeatedly with 0.01 M HCl to extract nonexchangeable K. The sequential extraction with 0.01 M HCl enabled to detect a significant depletion of nonexchangeable K in the root compartment, which was too small to be detected by conventional extractions with 1 M HNO_3 or 1 M HCl. This depletion was limited to the close vicinity of the roots, whereas depletion of exchangeable K extended up to 5 mm from the root compartment, and water-soluble K to a distance of 50 mm. The depletion in the root compartment (0.96 mg rhizobox^-1) amounted to about 5% of the K absorbed by the plant (19.4 mg rhizobox^-1). Although the percentage obtained in this study was smaller than that previously reported, the depletion of nonexchangeable K was detected with considerable sensitivity. These results suggest that sequential extraction with 0.01 M HCl is an effective approach for quantifying the slight, plant-induced depletion of nonexchangeable K in the rhizosphere.
社団法人日本土壌肥料学会の論文