THE EFFECT OF SEWAGE-SLUDGE ON ZINC CONTENT IN SOIL AND PLANTS

The effect of sewage sludge oil zinc (Zn) content in plants and soil w as examined in vegetation pot trials. Experiments were conducted in th ree different soils (Chernozem, Orthic Luvisol, Fluvisol) and on four crops (poppy, barley, corn, oats). Two types of sludge with average Zn contents were used. Direct and subsequent effects of sewage sludge we re studied. A trend of elevated Zn content in plants was observed afte r sludge applications. The highest values of transferfactor were deter mined in corn, oats and poppy seed. Average Zn uptake by crops amounte d to 30 to 43% of Zn dose in sludge. Zn utilization from sludges was c alculated by a balance method, and the values were within the interval of 4 to 13%. Zn content in soil was studied using different extractan ts (2M HNO3, 0.1M CaCl2, 0.01M CaCl2). Average proportion of Zn in 2M HNO3 was 41% out of Zn-tot in soils. An amount of 0.9 to 3.9% out of t he total Zn content in soils was released by 0.1M CaCl2 in relation to the soil type. The use of 0.01M CaCl2 resulted in extraction of 0.07 to 1.15% out of Zn-tot. The highest values of transferfactor were dete rmined in soil with the highest content of mobile Zn.