Slamförsök på åkermark i Skåne – 40 års erfarenheter av slamspridning

In this article, we present experiences from 40 years of field studies in Scania, southern Sweden, of sewage sludge application on arable land. The field studies have been conducted with the same trial plan at two locations outside the cities of Malmö and Lund, respectively. The trial plan includes nine combinations of sludge application and application of mineral fertilizer. Sludge application has resulted in increased crop harvest, increased content of soil organic matter and higher concentrations of soluble phosphorus. The crop uptake of the heavy metals cadmium, chromium, lead, mercury, nickel and zinc was the same whether sludge had been applied or not, while for copper the crop uptake was marginally higher in the sludge amended trials. In the soil, there were small or no effects of sludge application for cadmium, chromium, lead, and nickel, with 0-6 % increase of concentrations at “normal” sludge application (4 tons of sludge (dry weight)/ha every 4th year). Concentrations of zinc have increased with 6-14 %, mercury with 20-28 % and copper with 41-51 %. A multitude of organic pollutants have been studied, but high dilution in the soil, often high detection limits, and difficulties to assess the relative importance of sludge application versus atmospheric deposition, makes it difficult to draw safe conclusions. Future studies ought to focus on persistent pollutants, e.g. PFAS compounds, and on surface active substances, e.g., nonyl- and octylphenols, which are readily taken up by plants. The analyses of microplastics do not indicate that microplastics is a problem in sludge amended soils. Also, the study of antibiotic resistance showed that this is not a problem in sludge amended soils in Sweden at present.