In 2000-2001 at Piwnice (Kujawsko-Pomorski district), on podsolic soil (silty light loam), the influence of inter-crop of white mustard, farmyard manure application and autumn ploughing on the quality of sugar beet was investigated. Following variants were compared in the experiment: 1) farmyard manure with autumn ploughing (control), 2) autumn ploughing, 3) inter-crop of white mustard and autumn ploughing, 4) inter-crop of white mustard, farmyard manure and autumn ploughing, 5) inter-crop of white mustard - mulch. Highest sugar content was obtained in 2nd and 3rd variants - at sugar beet cultivation with farmyard manure, autumn ploughing and inter-catch crop of white mustard or without it. Sugar beet cultivated in mentioned variants and on mulch of white mustard showed relatively low a-NH₂-N content. Inter-crop of white mustard influenced on decrease of plant infestation by Erysiphe betae. Investigated factors did not cause intensified occurrence of Uromyces betae and Ramularia beticola.