Effects on the Content of Organic Matter, Nitrogen, Phosphorus and Heavy metals in Soil and Plants After Application of Compost and Sewage Sludge

This paper summarises the results of six years application of compost and sewage sludge on the content of the heavy metals in crops and on the content of organic matter, total nitrogen, available phosphorus and extractable heavy metals in soil. The trial was carried out on a three course rotation including winter wheat, sugar beet, maize; all the crops in rotation were grown each year. The soil was a silt loam with an average pH of 7.8 and an average CEC of 13.8 meq/100 g.The experiment consists of treatments with compost from sewage sludge and straw, liquid and dewatered anaerobic digested sewage sludge, at two rates (7.5 and 15 t of dry matter ha-1 yea-1) and of four treatments with only mineral fertilizers.The application of organic materials determined an increase of the Zn content in grains and in root and an increase of Cu in sugarbeet root. The other investigated heavy metals (Cd, Cr, Ni, Pb) have not shown significant differences in crops. The increase of the application rate had no effect on the concentration of heavy metals in plants; the application of liquid sludge resulted, some years, in a higher accumulation compared to dewatered sludge and compost. After six years of sludge and compost application, the soil showed an increase in organic matter, total nitrogen, available phosphorus, in extractable Zn and Ni. This increase was higher with the higher rate of application and, for Zn and P, with liquid sludge dressing.