Comparison of clay dispersion pretreatment and estimation of clay content in volcanic soils of Taiwan and the Philippines
2000
Asio, V.B. | Chen, Z.S. | Tsou, T.C.
Clay dispersion and determination are major problems in the study of Andisols. This paper reports the results of studies we conducted to find effective ways of dispersing clay and to estimate clay content from moisture content in such soils. The use of sodium hexametaphosphate (NaHMP), 0.1 M HCl to lower the pH to 4, and 0.5 M NaOH to raise the pH to 10 were compared as well as the use of air-dry and field-fresh samples. Clay was likewise estimated from the 1500kPa moisture using the formula: clay (%) = 1500 kPa moisture (%)/2.3. Results revealed that NaHMP was not only ineffective in enhancing dispersion but it also appeared to enhance flocculation except in one pedon. Only samples from one Andisol profile were dispersed by HCl while samples from three others dispersed only after NaOH pretreatment indicating that NaOH is suitable to more Andisols than HCl. The amount of measured clay was generally lower than the theoretical amount indicating poor clay dispersion. About 10 to 40% of the relative differences were observed in the amount of clay measured from air-dry and field-fresh samples implying that air-drying affected clay dispersion. The study also showed that the amount of clay of Andisols could be estimated from the moisture content at 1500 kPa. Such estimate can be even better than the measured amount for some Andisols, which are very difficult to disperse.
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