The investigations were carried out as a pot experiment comprising 7 fertilized objects in two series - the first set up in the autumn o f 2000 and t he second (with the same design) in the spring of 200 l. The experimental design was as follows: A - untreated control; B - mineral NPK; C - farmyard manure; D - sludge from biological- and-mechanical tannery sewage treatment plant; E - sludge from chemical tannery sewage treatment plant; F - sludge from biological- and-mechanical municipal sewage treatment plant at Niepołomice; G - sludge from biological- and- mechanical sewage treatment plant at Krzeszowice. Organic fertilizer doses were calculated on the basis of their nitrogen contents. The doses of essential fertilizer components were equal for all objects (except the control) and were as follows: 1.2 g N, 1.8 g P (for three years) and 1.4 g K·pot^-1. Maize, KOKA cv. was the test plant. Following the plant harvest, maize dry weight was determined. Heavy metal contents were determined after dry mineralization using atomic emission spectrometry with inductively coupled plasma (ICP-AES). Organic materials caused a significant increase in maize yields. The yields in the series fertilized in autumn were higher in the objects receiving organic treatment as compared to spring fertilization. In comparison to farmyard manure tannery biological sludge applied in autumn was the most yield forming. Sludge from municipal treatments also acted more favourably than farmyard manure at both dates of application. Diversification in heavy metal contents in maize above ground parts was significant and depended both on the date of application and form of fertilizers. The metal contents in the objects receiving organic treatment did not exceed limit numbers for fodder usefulness. As compared to the above ground parts, maize roots were more abundant in heavy metals.