SP rapport, 3: Langvarige mark- og lysimeterforsoeg med aarlig tilfoersel af store maengder tungmetalholdigt spildevandsslam.
1993
Larsen K.E. | Petersen J.
The object of these long term field and Lysimeter experiments on soils of different texture was to elucidate the agricultural value particularly of nitrogen the content of heavy metals in plant and soil and the leaching potential of nitrogen and heavy metals of dewatered anaerobically digested sewage sludge. Field experiments. During 1974-79 sewage sludge originating from a sewage treatment plants in a municipal town with relatively low-metal content and from one in an industrialized area with high-metal content was added annually at three experimental sites to a coarse sand a sandy loam and a loam soil. The treatment included 7 and 21 ton sand-free dry matter per ha applied to various agricultural and horticultural crops in rotation. The effect of sludge was compared to dressings of inorganic nitrogen and phosphorus in mineral fertilizers. Since 1980 the residual effect of sludge application was observed in a rotation of grass wheat fodder beet and spring barley. Lysimeter experiment. Plant uptake and leaching of nitrogen and heavy metals of sludge was investigated in a lysimeter experiment carried out during 1974-1987 on a coarse sand and loam soil. The treatments included yearly application in 1974-1981 of 400, 800 and 1600 g sludge per m2 and the residual effect being tested in the following years. The cropping sequence was spring barley, fodder beet, ital. ryegrass and oat. Nitrogen. The results of field experiments with annual application of sludge showed that sludge nitrogen was approximately 25 to 30 per cent as effective as fertilizer-N. Uptake of nitrogen expressed in percentage of applied N averaged 8-14 per cent for sludge compared to 43-51 per cent for fertilizer. Residual nitrogen effect of sludge application was on average of a five year period larger in crops with long growing season as fodder beet and grass both with and without addition of fertilizer N to previously sludge treated plots. Lysimeter experiments demonstrated that the use of large quantities of nitrogen in sewage sludge results in a substantial leaching of nitrogen especially after spring sown cereal. Metals There was a significant increase of Cu, Zn, Ni and Cd in herbage but no effect of Ca, Mg, Mn, Cr, Co and P contents. The concentration of Cd was smallest in grain and highest in green plant parts especially in tops of fodder beet. The increased uptake of cadmium persisted after application of sludge had ceased. Application of sludge increased the content of P, Cu, Zn, Pb and Cd in the surface soil (0-25 cm) according to the quantity of sludge added and its metal content. Eleven years after the last application of sludge Cd persisted in the top soil.
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