The aim of the research carried out in the years 1993–1996 was to determine the effect of organic (farmyard manure, rye straw, green manures based on post-harvest residues as well as on the whole biomass of the catch crop made up of the mixture of red clover and Italian ryegrass with and without the addition of straw) and mineral (0, 400, 600 kg NPK ha-1) fertilization on the content of dry matter and macroelements (N, P, K, Ca, Mg, Na) in the sugar beet leaves and roots. In the paper the effect on the chemical composition of sugar beet biomass of farmyard manure applied with the supplement of straw as well as green manures was compared. A field experiment was carried out at the Experimental Farm in Zawady, on the cereal-fodder strong soils, following the three-replication split-plot design. Independently of the mineral fertilization, the organic manures applied in the sugar beet cultivation, in most cases, significantly increased the dry matter, total nitrogen, potassium and calcium content in the roots, and the dry matter, total nitrogen, potassium, magnesium nad sodium content in the beet leaves, compared with the treatment without organic fertlization. Sugar beet fertilization with the rate of 400 kg NPK ha-1 resulted in a significant reduction of dry matter content in the beet roots and leaves and an increase in the total nitrogen, potassium, calcium and sodium content in the roots and leaves and, additionally, the magnesium content in the leaves, compared with the combination without mineral fertilization. The rate of 600 kg NPK ha-1 significantly reduced the dry matter content in the sugar beet roots and leaves and the calcium and sodium content in the leaves compared with the rate of 400 kg NPK ha-1. Moreover, the highest NPK rate increased the total nitrogen and potassium content in the beet roots and leaves and the magnesium content in the leaves. The effect of straw, the whole biomass and post-harvest residues of the catch crop with and without straw on the dry matter content in the sugar beet roots and leaves, the magnesium and sodium content in the roots and phosphorus, potassium, calcium, magnesium and sodium content in the leaves were significantly diverse, when related to the farmyard manure.