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This article in SSSAJ

  1. Vol. 42 No. 1, p. 94-97
    Received: May 16, 1977
    Accepted: Sept 23, 1977

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Residual Effects of Calcium Silicate in Tropical Soils: II. Biological Extraction of Residual Soil Silicon1

  1. R. A. Khalid and
  2. J. A. Silva2



A modified Neubauer seedling method utilizing rice (Oryza sativa, L.) as a test plant, was employed to study the bioavailability of residual Si in a Hawaiian Gibbsihumox soil. Adsorbed soil Si was also removed with 0.1N acetic acid adjusted to pH 3.5 and containing 50 ppm P (phosphate solution). The results show that more Si was extracted by plant and ratoon crops of rice combined than by phosphate solution because of longer extraction time during plant growth and also because of possibly greater efficiency of Si removal by rice roots. Rice seedlings extracted proportionately more native Si than did phosphate solution, which resulted in comparable amounts of applied Si being recovered by the two methods, i.e., 8 to 30% for rice and 13 to 23% for phosphate extraction. The results of this study show that 55 to 72% Si applied 5 years ago was still adsorbed by or precipitated in the soil in a form that these techniques could not measure. However, the findings of this study strongly indicate that the modified Neubauer technique can be efficiently employed to estimate the pool of potentially available soil Si in the highly weathered soils of the tropics.

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