Pedosphere 4(3): 279--284, 1994
ISSN 1002-0160/CN 32-1315/P
©1994 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Silicomolybdennm blue colorimetric determination of available Si in calcareons soils
XU Guo-Hua, ZHENG Wen-Juan, ZHAN Xin-Hua, LIU Ya-Kun and BAO Shi-Dan
Department of Natural Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095 (China)
      This paper deals with the determination of available Si content in calcareous soils with Mo blue colorimetric analysis method. The experimental results showed that two acid reagents of sodium acetate buffering solution (pH 4) and 0.025 mol/L citric acid generally had a strong ability of extracting soil available Si, and their soil filtrates were colorless. On the contrary, two alkaline extractants of 20 mg/mL sodium carbonate and 0.5 mol/L sodium bicarbonate only got a relevantly lower soil available Si and their extracts appeared deep color of organic and other pigments, which could be decolorized by adding certain amounts of P-free activated charcoal (about 0.1 g/g soil). In the procedure of Mo blue colorimetry, adding proper amount of oxalic acid and K(SbO)C4H4O6 could eliminate the interference of P to Si and Si to P, respectively. The concentration of acids was not the major factor suppressing the interferences between P and Si in the colorimetric analysis. In the medium of 0.2-0.8 mole H+/L sulfuric acid, the intensity of the silicomolybdate blue color did not vary with acidity, no matter whether (NH4)2Fe(SO4)2 or ascorbic acid was used as reductive reagent. About 10 minutes was needed to form a fully blue complex at 20-25℃. After 30 minutes, the blue color would slowly change into light one, and hence, the colorimetric process should be finished within a short time.
Key Words:  available silicon, calcareous soil, colorimetric analysis
Citation: Xu, G. H., Zheng, W. J., Zhan, X. H., Liu, Y. K. and Bao, S. D. 1994. Silicomolybdennm blue colorimetric determination of available Si in calcareons soils. Pedosphere. 4(3): 279-284.
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