Change Characteristics of Soil Weed Seed Bank in Tobacco Two-years Continuous Cropping System in Guizhou Province

The soil weed seed bank composition in tobacco fields of different biological area was investigated and studied by using the seedling germination method to make clear the change characteristics and trend of soil weed seed bank for prediction of weeds occurrence,dynamics and succession as well as guidance of integrated weeds management in tobacco field. The results showed that two-years tobacco continuous cropping had decreasing effect on soil weed seed bank species density and diversity,and the proportion of species density declined by 34. 03%. To single weed population,some weeds density keep relatively stable,like Digitaria sanguinalis,Conyza canadensis,et al. Whereas,other weeds,such as Mazus japonicus,Centella asiatica,seed density showed an increasing trend. Weed management was the leading cause to the change of weed seed bank in the same cropping system of the same region. And comparison of the same cropping system in the same area showed a relatively uniform vertical distribution of the weed seed bank density,and tobacco continuous cropping had little influence on the distribution of weed seed density in different soil depth. The emergence period of soil weed seed focused on the first germination mainly,and the number of the first two germination accounted for more than 96 % of the total soil weed seed germination. So late May to early June is a critical period for weed prevention and control in Guizhou tobacco fields.