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 was examined in vegetation pot trials. Experiments were conducted in three 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 were studied. A trend of elevated Zn content in plants was observed after sludge applications. The highest values of transferfactor were determined in corn, oats and poppy seed. Average Zn uptake by crops amounted to 30 to 43% of Zn dose in sludge. Zn utilization from sludges was calculated by a balance method, and the values were within the interval of 4 to 13%. Zn content in soil was studied using different extractants (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 the 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 determined in soil with the highest content of mobile Zn.