Abstract: In combination with indoor degradation test under controlled conditions,a field experiment was carried out in a bamboo forest on a hill slope in the subtropics of China to study distribution and fate of imazapyr in the soil,so as to guide safe use of the substance in similar regions.Results show that under laboratory conditions microbial degradation of imazapyr was quite slow in the soil,and degradation half life of the substance was 77 d,which might be attributed to the cause that imazapyr-degrading microbes in the soil of a pure bamboo forest were few in population or low in activity.In the field imazapyr residue was distributed mainly in the 0-20 cm soil layer.In the early days after imazapyr application when the concentration of the substance was high its loss through leaching and runoff with rainfall was significant,while in the late days after imazapyr application when the concentration of the substance was low,its degradation was little affected by rainfall,but mainly by soil microbes.Imazapyr has certain mobility and stability in soil.In case it is used in mountainous areas high in rainfall,attention should be paid to its possible impact on water sources,environment and biology in the downstreams. 

Key words: imazapyr, residual, distribution, microbial degradation, leaching, runoff