This paper deals with the determination of available Si content in calcareous soils with Mo blue colori-metric analysis method. The experimental results showed that two acid reagents of sodium acetate bufferingsoluti...This paper deals with the determination of available Si content in calcareous soils with Mo blue colori-metric analysis method. The experimental results showed that two acid reagents of sodium acetate bufferingsolution （pH 4） and 0.025 mol/L citric acid generally had a strong ability of extracting soil available Si, andtheir soil filtrates were colorless. On the contrary , two alkaline extractants of 20 mg/mL sodium carbonateand 0.5 mol/L sodium bicarbonate only got a relevantly lower soil available Si and their extracts appeareddeep color of organic and other pigments, which could be decolorized by adding certain amounts of P-freeactivated charcoal （about 0.1 g/g soil）. In the procedure of Mo blue colorimetry,adding proper amount ofoxalic acid and K（SbO）C<sub>4</sub>H<sub>4</sub>O<sub>6</sub> could eliminate the interference of P to Si and Si to P, respectively. Theconcentration of acids was not the major factor suppressing the interferences between P and Si in the colori-metric analysis. In the medium of 0.2-0.8 mole H￣+ /L sulfuric acid, the intensity of the silicomolybdate bltiecolor did not vary with acidity, no matter whether （NH<sub>4</sub>）<sub>2</sub>Fe（SO<sub>4</sub>）<sub>2</sub> or ascorbic acid was used as reductivereagent. About 10 minutes was needed to form a fully blue complex at 20-25℃. After 30 minutes, the bluecolor would slowly change intn light onet and hence, the colorimetric process should be finished within a shorttime.展开更多
文摘This paper deals with the determination of available Si content in calcareous soils with Mo blue colori-metric analysis method. The experimental results showed that two acid reagents of sodium acetate bufferingsolution （pH 4） and 0.025 mol/L citric acid generally had a strong ability of extracting soil available Si, andtheir soil filtrates were colorless. On the contrary , two alkaline extractants of 20 mg/mL sodium carbonateand 0.5 mol/L sodium bicarbonate only got a relevantly lower soil available Si and their extracts appeareddeep color of organic and other pigments, which could be decolorized by adding certain amounts of P-freeactivated charcoal （about 0.1 g/g soil）. In the procedure of Mo blue colorimetry,adding proper amount ofoxalic acid and K（SbO）C<sub>4</sub>H<sub>4</sub>O<sub>6</sub> could eliminate the interference of P to Si and Si to P, respectively. Theconcentration of acids was not the major factor suppressing the interferences between P and Si in the colori-metric analysis. In the medium of 0.2-0.8 mole H￣+ /L sulfuric acid, the intensity of the silicomolybdate bltiecolor did not vary with acidity, no matter whether （NH<sub>4</sub>）<sub>2</sub>Fe（SO<sub>4</sub>）<sub>2</sub> or ascorbic acid was used as reductivereagent. About 10 minutes was needed to form a fully blue complex at 20-25℃. After 30 minutes, the bluecolor would slowly change intn light onet and hence, the colorimetric process should be finished within a shorttime.
