A thermostatic incubation experiment was carried out to estimate the effects of flooding periods, stalk application and P addition on Fe transformation and P availability in calcareous soils. Submergence increased amo...A thermostatic incubation experiment was carried out to estimate the effects of flooding periods, stalk application and P addition on Fe transformation and P availability in calcareous soils. Submergence increased amorphous Fe, especially in the case of stalk application. The newly formed amorphous Fe with a great surface area played an important role in P sorption; and submergence also stimulated the dissolution of inorganic P, thus increasing the availability of soil P in calcareous soils. Meanwhile, a part of soluble P was adsorbed and fixed again on the surface of newly formed amorphous Fe, thus resulting in a decrease of P availability. Soil rapidly available P increased after ISO-day incubation. There existed significantly negative correlations between soil amorphous Fe content and soil Fe-P and rapidly available P contents. Submerged conditions promoted the transformation of inorganic P added to-ward Fe-P in calcareous soils, especially in the case of stalk application.展开更多
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
Soil test for availability of nutrients and heavy metals is extensively served as a means for the evaluations of soil fertility, and environmental effects and phytotoxicity of pollutants in soils, and for the fertiliz...Soil test for availability of nutrients and heavy metals is extensively served as a means for the evaluations of soil fertility, and environmental effects and phytotoxicity of pollutants in soils, and for the fertilizer recommendation in agricultural and environmental sciences. Therefore, great attention has been paid to the measurement of elemental availability in soil test.展开更多
基金A part of the project supported by the Laboratory of Material Cycling in Pedosphere, Academia Sinica.
文摘A thermostatic incubation experiment was carried out to estimate the effects of flooding periods, stalk application and P addition on Fe transformation and P availability in calcareous soils. Submergence increased amorphous Fe, especially in the case of stalk application. The newly formed amorphous Fe with a great surface area played an important role in P sorption; and submergence also stimulated the dissolution of inorganic P, thus increasing the availability of soil P in calcareous soils. Meanwhile, a part of soluble P was adsorbed and fixed again on the surface of newly formed amorphous Fe, thus resulting in a decrease of P availability. Soil rapidly available P increased after ISO-day incubation. There existed significantly negative correlations between soil amorphous Fe content and soil Fe-P and rapidly available P contents. Submerged conditions promoted the transformation of inorganic P added to-ward Fe-P in calcareous soils, especially in the case of stalk application.
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.
文摘Soil test for availability of nutrients and heavy metals is extensively served as a means for the evaluations of soil fertility, and environmental effects and phytotoxicity of pollutants in soils, and for the fertilizer recommendation in agricultural and environmental sciences. Therefore, great attention has been paid to the measurement of elemental availability in soil test.
