The small-plot experiment with sewage sludge compost (SSC) was started in the spring of 2003. Soil type is acidic Arenosol at the Research Institute of Nyíregyháza, University of Debrecen, in the NE part of Hungary. The applied SSC contained 40% of sewage sludge, 25% of straw, 30% of rhyolite and 5% of bentonite. Four treatments in five blocks have been conducted, where the SSC was applied at a rate of 0, 9, 18 and 27 t ha-1 and then was ploughed into the soil. Treatments were repeated in 2006, 2009, 2012 and 2015. Test plants were maize (Zea mays L.), triticale (x Triticosecale x Wittmack) and green pea (Pisum sativum L.) followed each other in a crop rotation every year. Composite soil samples were mixed from 5 subsamples in each plot from 0-30 and 30-60 cm soil layers after harvesting of test plants. Experimental results showed that composted sewage sludge application had positive effects on the chemical properties of the soil, especially the increase of pH and humus content.
Keywords: long-term experiment, sewage sludge compost, chemical properties of soil, bentonite, Arenosol