Retention and release of diquat and paraquat herbicides in soils
1993
Kookana, R.S. | Aylmore, L.A.G. (Western Australia Univ., Nedlands. Soil Science and Plant Nutrition)
In some Western Australian soils varying in physical and chemical properties, sorption isotherms for diquat and paraquat were found to be of the 'L' type according to the Giles classification with the data fitting well to the Langmuir equation. The sorption capacities of soils for diquat ranged from very high in clay soil to very low in sand and followed the order of clay content in the soils. The clay soil also showed the highest value for the Langmuir coefficient representing bonding energy. Both the type and content of clay minerals present in soil were important for sorption and subsequent desorption. An increase in the salt concentration of the soil solution resulted in decreases in sorption capacities. Both Ca2+ and Na+ cations competed for the sorption sites with the herbicides, but Na+ was not as effective as Ca2+. Desorption of the herbicides was also significantly affected by the salt concentrations of the extractant. Desorption of diquat was higher than that of paraquat at all salt concentrations. Hysteresis was evident between sorption and desorption isotherms. As sorption increased, the desorption became easier, indicating that the herbicides were less strongly held. Sorption which occurred in the presence of higher ionic strength solutions of inorganic cations was relatively less susceptible to desorption.
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