| Allicin is a kind of fungicide within the organic sulfur, which is recommended as a herbicide in our country.In tobacco fields, it was always used in preventing tobacco.bacterial wilt. In order to evaluate whether it is risks to the eco-environment in tobacco, this paper has systematically studied the residual degradation in tobacco and soil after it was applied in tobacco field, its transportation in "soil-tobacco" system, its adsorption and the effect on enzyme activity in planted tobacco soil. The main conclusions were as follows:(1) With GC technology, the methods of residual analysis and determination of allicin in tobacco and soil planted tobacco were established and improved by adding recovery test. Under the experimental conditions, when the spiked level of 0.05,0.50, 1.00 mg/kg in blank samples of planted tobacco soil fresh tobacco leaves and dry tobacco leaves, the average recoveries of allicin were between 84.42% and 104.12%, and the coefficient of variation between 1.10% and 3.54%; the minimum detectable amount was 1.0×10-11 g; the minimum detectable concentration of allicin were 1.25×10-3 mg/kg in the planted tobacco soil,1.25×10-3 mg/kg in the fresh tobacco leaves and 2.50×10-3 mg/kg in the dry tobacco leaves. It showed that the method can be used to study the residual behavior of allicin in the tobacco fields.(2) Under natural conditions in China, the degradation of allicin followed a equation of one-grade chemical reaction kinetic equation in in the planted tobacco soil and the tobacco leaves, and the degradation half-life of allicin was 1.55 d,1.73 d in the planted tobacco soil from Hunan Changsha and Shandong Qingdao respectively, with an average half-time of 1.64 d; the degradation half-life was 0.90 d,1.13d in tobacco leaves respectively, with an average half-time of 1.02 d.(3) The final residue indicated that when the tobacco plant was irrigated and sprayed 3 to 4 times with 30% allicin in the dosage of 6250.5ml/hm2 (irrigate root),3125.3ml/hm2 (spray)and 9375ml/hm2 (irrigate root),4687.5ml/hm2 (spray) respectively, each application interval for seven days. When the last application was done after 21 days, the residues of allicin in the planted tobacco soil ranged from 0.001 to 0.004 mg/kg; the residues of allicin in the dry tobacco leaves were no detected. This suggests that during the baking process,all the allicin was degradation or volatile. So it was concluded that it is safe that the 30% allicin was used in the tobacco fields.(4) In the system of "Soil-tobacco," the allicin can transport from in planted tobacco soil to tobacco leaves, and the order of residues in different position of tobacco leaves was:lower leaves> middle leaves> upper leaves.(5) The invertase activity was significantly influenced by allicin,and could be described as a process of inhibitionâ†'activation. and the effect of allicin on urease activity was that:the time of activation was longer than inhibition time,and the trend performed as the process of reinstationâ†'inhibitionâ†'re-activation. But the effect of allicin on catalase activity was not obcious, and effects of allicin with different concentration on catalase was similar, the general trend performed as the process of activationâ†'inhibition.(6) Soils had strong adsorption of allicin, which, however, varied with the different properties of the soil tested. The isotherm data were fitted to the Frenundlich equation. The adsorption capacity increased with increasing organic matter and CEC of the soils and decreased with increasing PH. The free energy of sorption(â–³G) ranged from 15.93 to 18.53kJ/mol indicates the spontaneity of the given sorption process of allicin soils. |
PDF Full Text Request