The purpose of the study was the influence of different forms of fertilizers used in potato cultivation on humus and organic carbon content in ploughing light soil layer and the quality of humus. The experiment was conducted at the Experimental Station of Department of General Plant and Soil Cultivation in Mydlniki near Kraków, Poland. In the potato cultivation technology there were used: mineral fertilizing, manure, straw from winter triticale, spring barley and peas. Organic fertilization was used with mineral one. The cultivation was carried out after winter triticale with ploughed stubble intercrop or without it. The biggest humus increase was noted after manure and stubble intercrop fertilizers. On the basis of laboratory analyses a higher content of soil organic carbon was found after fertilizing soil with white mustard biomass and with manure. In the tested objects a higher content of mean values C/N was stated in a ploughing layer with stubble intercrop ploughted in.