The field research was carried out in the years 2000-2003 at the Experimental Farm of Lublin Agricultural University, located in Bezek near Chełm (51^o19’ N; 23^o26’ E). The purpose of this work was to determine the influence of the number and dry matter of weeds on potato tuber yield and its structure with organic and mineral + organic fertilization applied in comparison with the control without fertilization, depending on the soil agronomical category. The results indicated significant negative relationships between weedness indicators (the number and mass of weeds) and potato tuber yield. The total yield of potato tubers on heavy soil was also significantly negatively correlated with the number of monocotyledonous weeds at both times of weedness observation. On light soil these relationships occurred only prior to row closing. Air-dry matter of weeds and the total number of weeds induced the increase in yield of the smallest tubers at the cost of the yield of the most valuable fractions (from 50 to 60 and more than 60 mm).

125-132