Germination and juvenile development of plants on municipal solid waste incineration (MSWI) slag

In order to find sufficient greening measures for MSWI slag deposits, germination and juvenile plant growth on fresh as well as artificially aged municipal solid waste incineration slag were investigated for seeds of three widely used commercial test species (Phleum pratense, Lepidium sativum, and Trifolium alexandrinum) and the widespread weed Amaranthus retroflexus. Adapted Austrian standard tests comprised 2 moisture levels, 2 slag types and 4 different slag concentrations. L. sativum grew well on aged slag, whereas its juvenile growth was clearly inhibited on fresh slag. The grass P. pratense performed better on fresh than on aged slag. Under moist conditions A. retroflexus grew well on aged and on fresh slag, but was the only species with a marked germination delay throughout all mixtures of aged slag. The species with the most continuous development under all conditions was T. alexandrinum. Even on pure aged slag it grew sufficiently under moist conditions. Moderate portions of even fresh MSWI slag do not necessarily inhibit plant germination and growth; only pure slag has a negative effect throughout all species. For successful greening of MSWI slag, various substrate properties like water holding capacity and soil texture seem to be as relevant as nutrient supply, toxicity, salinity and extreme pH.