This study is based on the results of the field experiment carried out in 1990-1992 on the soil of mechanical composition of light loamy sand. The yield and tuber structure of the crop of potato tubers of 37 varieties were evaluated. A positive effect on the crop and mass of the tubers of ϕ 4-5, 5-6 and >6 cm was exerted by the July and August rainfalls, the May and June rainfalls resulted in enlarging the tuber mass by ϕ <3 cm, and decreasing the share of the remaining tuber size fractions. The increase in atmospheric temperature in July and August caused a drop in tuber yield, and also the tuber mass of ϕ 5-6 and >6 cm in diameter. Heightening by a unit the abundance of assimiable phosphorus and potassium in the soil at its mean level of 15.7 and 21.9 mg/100 g soil, respectively, resulted in an increase of tuber mass in the crop by $ <3, 3-4, 4-5 cm, and a lowering of tuber mass in the largest crop. The transition from slightly acid to neutral soil reaction caused a drop in the crop as well as the proportions of small and medium tubers and an increase in the share of marketable tubers.