Effect of municipal sewage sludge on winter rape and soybean production and heavy metal contamination of soil

Abstract

Investigations conducted during 2004-2008 at the Podu-Iloaiei Agricultural Research Station have studied the influence of different rates of sewage sludge on yield and soil agrochemical characteristics. Sewage sludge was applied annually at rates of 20, 40 and 60 t/ha, together with mineral fertilizers, differentiated according to the growing plant. Applying rates of 20 t/ha DM sewage sludge resulted in the accumulation of mobile phosphate stock in soil of 58 ppm; the microelement content (mobile forms from soil) was of 19.0 ppm at Cu, 0.51 ppm at B, 149 ppm at Zn and 397 ppm at manganese. The obtained results have shown that by applying a rate of 30 t/ha of raw sewage sludge (18.5 l t/ha dry matter), the allowable maximum limits stipulated by Norm 86/278/EEC, were not exceeded. By applying rates of 60 t/ha raw sewage sludge (37 t/ha dry matter), the limits established by Norm 86/278/EEC and Order no. 49 from January 14, 2004 have been exceeded only at zinc. The application of the rates of 40 t/ha sewage sludge has resulted in increasing the degree of plant supply by mineral elements (especially, nitrogen and phosphorus). It has also resulted in a mean annual supply of 3.8 t/ha highly humificated organic matter; this explains the increase in soil humus content (after 4 years) from 2.82 to 3.79%. The use of fermented sewage sludge, at a rate of 40 t/ha, has resulted in getting mean yield increases of 65 % (1075 kg/ha), in winter rape, and of 63 % (937 kg/ha), in soybean. For slope lands degraded by erosion, sewage sludge with other organic resources may contribute to the improvement in soil characteristics. The application of rates of 20 t/ha sewage sludge DM has resulted in the accumulation of mobile phosphates in soil of 58 ppm, and the content of microelements, mobile forms from soil, was of 19.0 ppm at Cu , 0.51 ppm at B, 149 ppm at Zn and 397 ppm at manganese.