Saturday, 15 July 2006

Study on The Adsorption of Bensulfuron-methyl by Main Zonal Soils in Central-South China Region.

Tian-Zhi Ouyang, Dept of Applied Chemistry, Wuhan Univ of Technology, 122 Luoshi Road, Wuhan, 430070, China and Xue-yuan Li, College of Resources and Environment, Central China Univ of Agriculture, No.1 , Shizishan, Wuham, 430070, China.

BenSulfuron-Methyl (BSM, a sulfonylurea herbicide) used widely in the paddy fields of central southern China region has good weeding results for most broad leaf and Cyperus rotundus weeds. A small amount of BSM remained in soil might be produce medicinal poisoning to the following susceptible corp. For providing prevention and cure measures to the toxicity of remainder BSM on main zonal soils in central southern china region were studied based on the adsorption/desorption of herbicide in soil was a predominant factor for its behavior and end result in soil-water environment. The main results and progresses are as follows: 1.The adsorption amount of BSM on testing soils increased with rising BSM concentration in equilibrium solution and the adsorption process could be better described by using Langmuir equation but only in part of them could be better described by using Fruendlich equation, which indicated that the adsorption of BSM on testing soils was more conformable to monomolecular layer adsorptive model. 2.Most adsorption isotherm curves of BSM-pH on testing soils belong to L-type, only the curves at pH 4 for Oxisol and Alfisols tested belong to H-type. This was consistent with the magnitude of their binding energy, the formers are low affinity-type whereas the latters are high affinity type. 3.The maximum adsorbing capacity (Bmax) of BSM on testing soil decreased with rising the pH value in equilibrium solution and the reducing degree varied with the various soils. The Bmax of BSM on Oxisol,Ultisols and Alfisols reduced from 20.46,19.15-16.5 and 13.17-13.61 gg-1 in pH 4 equilibrium solution to 6.68,10.45-6.1 and 9.66-9.31gg-1 in pH 8 equilibrium solution respectively. Namely the amount of BSM adsorbed on Oxisol under the acid condition was remarkably higher than that of Alfisols and it was opposite under slight alkalinity condition. The reason was related to the different testing soils with various contents and constituents of clay mineral or clay oxides, which produced different surface charge characteristics, PZC and electrokinetic behavior in various pH equilibrium solution. These result in that the remnant and transference of BSM in soil varied with various soils. Sum up the result and discussions mentioned above we reposed that: (1)The remainder of BSM on Oxisol mainly occurred in soil surface horizon owing to its acidity, high absorbing capacity and affinity. (2)The remainder BSM on Alfisols only a partly occurred in surface horizon, the other parties may be transference to the lower horizon or in the ground water. Therefore the prevention and cure measures to the toxicity of remain BSM should different with various soils.

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