A status of vegetation developing on arable field during first year of set aside the field was presented in the paper. Investigations were carried out on loess soil during three seasons, in the 1995/6-1997/8. Fifty four species were noticed in the study. They were the weeds of arable lands; the short-living once played a main role among them, constituting of 93-76% of species and 99-95% of individuals in a community. The flora has dynamically changed in the course of seasons (autumn-spring-summer). It has been distinguishable in the changes of their density, as well as in the value of ecological indexes used to assessment of inside phytocenoses arrangement. Only biodiversity index linearly increased when seasons proceeded, while different way did two other indices � dominance and evenness. Chenopodium album and Apera spica-venti were the most abundant species at the fallow-field.