Effect of Plant Species on Degradation of Butachlor in Rhizosphere Soils Collected from Agricultural Field

Plant rhizosphere provides a favorable microecosystem for the proliferation of soil microorganisms and therefore vegetation can promote actively microbial degradation of organic chemicals in soil. The degradation of herbicide butachlor in nonrhizosphere soil and in rhizosphere soils after vegetation of crop plants was studied. The results showed that the degra dation rate of butachlor in soil was accelerated markedly after vegetation of cotton, rice, wheat, and corn plant, and the halflives of butachlor, at concentration of 15 mg/kg, in these rhizosphere soils, were shorten by 26.6% to 57.2%, respectively, compared to those in nonrhizosphere soil. The enhancement of the degradation activity increased with species of crop plant in the order of corn, wheat, rice and cotton. Although butachlor at high concentration (50 mg/kg) showed some degree of inhibition, the degradation was also enhanced by vegetation of the crop plants. Measurement of the growth of butachlor degraders during the degradation experiment period indicated that the number of butachlor degraders in rhizosphere soils was larger than that in nonrhizosphere soil. Our results suggest that vegetation of a certain crop plants may accelerate removal of residual herbicides and avoid residual toxicity to crops.