Effects Of Surfactant On The Behavior Of Bendazone In Different Soils

Bentazone, a contact and selective contact herbicide, is mainly used to remove post-emergency weeds. In China, bentazone, which shows advantages of efficiency, broad spectrum and low toxicity, is widely used in paddy fields, wheat fields and fruit farms. However, along with the stable and great harvest of agricultural yield brought by the massive application of bentazone, a series of ecological and environmental problems appear. This paper studied the absorption behavior of bentazone in different soils and analyzed the dynamic absorption changes of bentazone in the soil after surfactants were added, for the purpose to control the absorption behavior of bentazone in the soil by using surfactants and so that to enhance the quality safety of agricultural products and realize the sustainable agricultural development.a. Oscillation in batches:when the soil-solution ratio is 1:5 (5g soil:25mL solution), sample soil oscillated for 2h showed rapid absorption effects to bentazone; continue oscillating for another 2h and the absorbing capacity of bentazone in the soil increased but in little amount. Nevertheless, all the absorption-related physical and chemical reactions were still in process. Thus, the equilibrium time between the absorption-desorption experiments was determined to be 24h. In the absorption experiment, the absorption equilibrium of bentazone in water-soil (red soil of Xuancheng and moisture soil of Bozhou) system showed non-linear features and such equilibrium can be verified and described by Frenundlich equation. It was clear by comparing the values of constant Kd that the little bentazone could be absorbed in the soil and the absorption rate of bentazone in the red soil of Xuancheng was greater than that in the moisture soil of Bozhou and this is greatly contributed by the texture and composition of soil. Red soil of Xuancheng contained greater amount of clay particles than Bozhou moisture soil. Koc can be calculated through the value of Kd: Koc=(Kd×100)/C% (Kd is the absorption rate while C% is the percentage of organic carbon in the soil). The herbicide shows high mobility when Koc<50 and relatively small mobility when 50<Koc<100. Calculation showed that Koc of both the Xuancheng red soil and Bozhou moisture soil were smaller than 50, which means that bentazone has strong mobility in Xuancheng red soil and Bozhou moisture soil and will correspondingly contaminate the underground water.b. It was found that, after adding the anionic surfactant SDS, when the concentration was lower than 100% critical micelle concentration (CMC) of SDS, bentazone showed constantly decreasing absorbing capacity along with the increase of SDS concentration and dropped to the minimum at 2300 mg·L"- (about 100% CMC); in the contrast, when the concentration was higher than 100% CMC, bentazone showed constantly increasing absorbing capacity along with the increase of SDS concentration. Because SDS at low concentration may exist in the solution in the form of monomer and thus compete with bentazone for absorption sites in the soil, the absorbing capacity of bentazone in the soil will then decrease; however, when the concentration is higher than 100% CMC, the surfactant SDS may produce semi-micelle and thus further enhance the absorbing capacity of bentazone in the soil,c. In the presence of cationic surfactant CTAB, the absorbing capacity of bentazone in the soil was obviously higher than that of the control group, and the absorption coefficient was multiples of that of bentazone without the cationic surfactant. Thus it was clear that adding CTAB could enhance the absorbing capacity of bentazone in the soil; furthermore, together with the concentration increase of CTAB, the absorbing capacity increased too. It was because that the soil carried negative charges itself and showed absorbing capacity, thus most exchangeable cations might exchange intensively with CTAB and thus be absorbed to the soil. As a result, the surface property of the soil changed from hydrophilic to hydrophobic and thus the absorbing capacity of the soil was enhanced.