Evaluation of readily available nonexchangeable potassium in soil by sequential extractions with 0.01 molar hydrochloric acid |
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| Authors: | Naoki Moritsuka Junta Yanai Ayane Fujii Shuji Sano Takashi Kosaki |
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| Institution: | 1. Laboratory of Soil Science, Graduate School of Agriculture , Kyoto University , Kyoto, 606-8502, Japan;2. Education and Research Center for Biological Resources , Shimane University , Matsue, 690-1102, Japan E-mail: morituka@life.shimane-u.ac.jp;3. Laboratory of Soil Science, Graduate School of Agriculture , Kyoto University , Kyoto, 606-8502, Japan;4. Miyazaki Prefecture (Koyu Norinshinko-kyoku) , Takanabe, Miyazaki, 884-0002, Japan |
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| Abstract: | Nonexchangeable potassium (K-ne), i.e. 1 M NH4OAc-nonexchangeable K, often contributes significantly to plant nutrition. However conventional extraction methods often extract much more K-ne than plants even after intensive cropping, suggesting the difficulty in evaluating the amount of readily available soil K-ne. In this study, we used a milder extraction method (0.01 M HCl method) to examine its applicability to evaluate the amount of readily available K-ne in soil. In the first experiment, the concentration of K-ne in twenty surface soils sampled from agricultural fields in Japan and K-bearing minerals was determined by the 0.01 M HCl method, i.e. sequential extraction with 0.01 M HCl over a period of 10 d after removal of exchangeable K, and by conventional methods. The average percentage of the soil K-ne extracted by the 0.01 M HCl method amounted to 0.66% of the total K amount, and was much lower than that by a single extraction with 1 M HNO3 (2.0%) or with 0.2 M sodium tetraphenylboron for 2 d (22%). In the second experiment, the amount of K-ne removed by chemical extractions was compared with that of K-ne removed by maize plants grown for 29 d in five of the above soils. The amount of the K-ne evaluated by the 0.01 M HCl method gave the highest correlation (p < 0.05) with that of the K-ne utilized by plants among the extraction methods applied. The amount of soil K-ne extracted by the 0.01 M Hel method could therefore become a suitable index of the amount of readily available K-ne in soil. Extraction of K-ne in soils after maize planting further indicated that plants had removed K-ne more intensively than the 0.01 < HCl method probably only from the rhizosphere, although a high correlation was observed between the amount of K-ne removed by the 0.01 M Hel method and that by plants. This implies that the estimation of the amount of K-ne utilized by plants requires not only soil chemical analysis but also the evaluation of the percentage of the soil volume where the plant-induced release of K-ne actually occurs. |
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| Keywords: | 0 M HCl" target="_blank">01 M HCl maize nonexchangeable potassium rhizosphere sequential extraction |
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