The purpose of the study has been to determine the direct and residual effect of farmyard manure and composts made from sewage sludge on the content and uptake of copper and zinc by crops growing in a four-field crop rotation system. In 2004-2007, a field experiment was established on proper grey-brown podzolic soil, originating from light boulder clay, rich in P, moderately abundant in K and low in Mg, whose reaction was pH = 5.04. The experiment involved a four-field crop rotation cycle with the following crops: potato, spring barley, winter oilseed rape and winter wheat. The design of the experiment, set up according to the random block method, consisted of 8 object (2 x 4): 1) FYM, 2) composted sewage sludge, 3) compost (sewage sludge + straw), 4) dried and granulated sewage sludge. The composts and farmyard manure were applied once in the rotation system (under potato) at a rate of 10 t d.m. ha-1 or twice, each time 5 t d.m. ha-1 (under potato and under winter oilseed rape). In the objects fertilized with organic fertilizers and manure, nitrogen was balanced to 150 kg⋅ha-1 (under potato) and to 120 kg⋅ha-1 (under oilseed rape) depending on their total content of nitrogen. Spring barley and winter wheat received only mineral fertilizers. Before the experiment was set up, samples of soil, manure and composts had been collected for determination of Cu and Zn in 1 mol HCl dm-3 by atomic absorption spectrophotometry.

The aim of this study has been to determine the indirect and direct effects of farmyard manure and sewage sludge composts, produced in the north-eastern part of Poland, on the content of 1 mol HCl⋅dm -3 soluble forms of zinc and copper in soil.In 2004-2007, a field experiment was carried out at the Experimental Station in Ba³cyny near Ostróda. The experiment was established on proper grey-brown podzolic soil originating from light boulder clay, which was rich in P, moderately abundant in K and low in Mg. It comprised a four-field crop rotation system (potato, spring barley, winter oilseed rape and winter wheat. The design of the experiment, set up according to the random block method, involved 8 objects (2 x 4): 1) farmyard manure, 2) compost (sewage sludge + straw), 3) dried and granulated sewage sludge, 4) composted sewage sludge. The composts and FYM were introduced to soil once (in 2004) at a rate of 10 t d.m.⋅ha -1 or 2 × 5 d.m.⋅ha -1 (under potato and winter oilseed rape). In 2004, nitrogen in the soil enriched with natural fertilizers was balanced to 150 kg⋅ha -1 according to the N-total content. In 2005, soil cropped with spring barley received only mineral fertilization, whereas winter oilseed rape received the second rate of organic fertilizers (in the series consisting of 2 × 5 d.m.⋅ha -1 ) and nitrogen was balanced to 120 kg⋅ha -1 . In 2006, soil under winter wheat received only mineral fertilization.Prior to the establishment of the experiment, soil, manure and compost samples were taken. Having been averaged, the samples were subjected to determination of their content of Cu and Zn in 1 mol HCl dm -3 .