The study was carried out in 2003–2004 on the field which had been left fallowed for the last 3–4 years, on loess soil. Thirteen species of weeds were thoroughly analysed. The purpose of the analysis was assessing their prolificacy in relation to the selected biometric features. Each species was represented by 30 specimens. On the basis of each plant's seed numbers the average, minimal and maximal numbers of seeds for species were given in the table.
Among the most prolific were: Daucus carota, Conyza canadensis and Matricaria inodora, and the least prolific were Vicia grandiflora, Stachys palustris and Lithospermum arvense. Seed production of the studied weed species was significantly correlated with their air-dry weight and the number of fruits or fruit sets. Also, the correlation of seed production and the height of plants was found for Bromus secalinus, Viola arvensis, Stachys palustris, Centaurea cyanus and Vicia hirsuta. Among the discussed biometric features the weight of one thousand seeds and plant's height revealed slight deviation, while the number of fruits or fruit sets and air-dry weight – strong deviation from the average values.