The effects of topsoil thickness on winter annual weed growth and nutrient concentration were assessed for three consecutive years in soybean plots. The topsoil treatments had high fertility levels, uniform textures, and no herbicides were used in the study. Common chickweed composed 75% of the winter annual weed species. Weed biomass production decreased as topsoil thickness decreased from 22.5 cm to 0. Topsoil thickness of 22.5 cm produced 800 kg ha–1 more weed growth than 0 cm topsoil. The weed biomass grown in thicker topsoil had higher total amounts of N, K, Mg, and Ca.