Pedosphere 6(4): 349--354, 1996
ISSN 1002-0160/CN 32-1315/P
©1996 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Effects of humic acid and solution pH on dispersion of Na- and Ca-soil clays
LAN Ye-Qing, HU Qiong-Ying and XUE Jia-Hua
Applied Chemistry Department of Naniiny Agriculturul University, Nanjiny 21O095 (China)
      Dispersed soil clays have a negative impact on soil structure and contribute to soil erosion and contaminant movement. In this study, two typical soils from the south of China were chosen for investigating roles of pH and humic acid (HA) on dispersion of soil clays. Critical flocculation concentration (CFC) of the soil clay suspension was determined by using light transmission at a wavelength of 600 nm. The results indicated that effects of pH and HA on dispersion of the soil clays were closely related to the type of the major minerals making up the soil and to the valence of the exchangeable cations as well. At four rates of pH (4, 6, 8 and 10), the CFC for the Na-yellow-brown soil treated with H2O2 was increased from 0.32 to 0.56, 6.0 to 14.0, 10.0 to 24.6 and 26.0 to 52.0 mmol L-1 NaCl, respectively when Na.HA was added at the rate of from 0 to 40 mg L-1. With the same Na-HA addition and three pH (6, 8 and 10) treatments, the CFC for the Na-red soil was increased from 0.5 to 20.0, 1.0 to 40.0 and 6.0 to 141.0 mmol L-1 NaCI, respectively. Obviously, pH and HA has greater effects on clay dispersion of the red soil (dominated by 1:1 minerals and oxides) than on that of the yellow-brown soil (dominated by 2:1 minerals). However, at three rates of pH (6, 8 and 10) and with the addition of Ca-HA from 0 to 40 mg L-1, the CFC of the Ca-yellow-brown soil and Ca-red soil treated with H2O2 was increased from 0.55 to 0.81, 0.75 to 1.28, 0.55 to 1.45 and 0.038 to 0.266, 0.25 to 0.62, 0.7 to 1.6 mmol CaCl2 L-1, respectively. So, Na.soil clays are more sensitive to pH and HA than Ca-soil clays.
Key Words:  clay, dispersion, humic acid, pH, soil
Citation: Lan, Y. Q., Hu, Q. Y. and Xue, J. H. 1996. Effects of humic acid and solution pH on dispersion of Na- and Ca-soil clays. Pedosphere. 6(4): 349-354.
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