The Effect of Compost Made With Sewage Sludge on Heavy Metal Content in Soil and in Lolium Multiflorum Lam

The aim of this paper is to assess the effects of different doses of sewage sludge compost mixed with wheat straw on heavy metal content in Italian ryegrass and in soil. A two year experiment with the Italian ryegrass was set up in autumn 2012. The experimental design consisted of a control plot, a plot with NPK fertiliser and three plots with three different doses of municipal sewage sludge compost (5, 10 and 15 Mg of fresh matter·ha^-1). Those different compost doses contained the amounts of Nitrogen equivalent to 60, 120 and 180 kg·N.ha^-1. The two lower doses of compost were supplemented with nitrogen fertiliser so that the amount of this chemical element introduced to the soil of all plots with compost stood at 180 kg·ha^-1. During 2013 and 2014 seasons the grass was cut three times a year after about a 30-day growing period. After dry mineralisation, the content of Zn, Cu, Ni, Pb and Cd in the plant samples was measured with the ICP-AES method. The fertilisers applied significantly diversified the content of chemical elements in the grass and in the soil. The highest dose of compost resulted in the highest concentration of Zn, Cu and Cd in the grass while the highest concentration of Ni and Pb was in the soil and the grass from the plot where the mid dose of compost had been applied. Cadmium concentration in the soil was the highest in the plot where the mid dose was applied. The experiment proved that compost made with sewage sludge and wheat straw is beneficial for plants.