POTENTIAL USE OF PLANT RESIDUE WASTES IN FORESTS OF NORTHWESTERN GERMANY

Increasing amounts of waste and limited space for its deposition requi re alternative waste management practices, such as the use of organic wastes for amelioration of forest soils. The effects of plant residue waste application to forest soils were assessed by laboratory incubati on, and by field experimentation at two sites with contrasting soil pr operties. The wastes used were a fresh and shredded material and a mat ure compost, both from plant residues, and were nutrient rich with hig h contents of bases and low concentrations of heavy metals. Long-term laboratory incubation showed no difference in total N mineralization b etween fresh organic waste, mature organic compost and beech litter. T he nitrification rates in the organic wastes were higher, however. Car bon dioxide evolution was higher from fresh organic waste, and lower f rom mature organic compost than for beech litter. Neither liming nor a ddition of different soils, which served as inocula, significantly inf luenced N or C mineralization in wastes. Of total potassium in fresh o rganic waste 80% was released during a 67 day incubation period. Seepa ge water samples from an acid brown earth and a Terra fusca-Rendzina s ite showed negligible differences between concentrations of most most elements for waste application and control plots. However, in both soi ls potassium and chloride concentrations were highest under mature com post. After 21 months, the pH of humus and mineral soil below waste la yers had not increased. The basicity of waste will deacidify acid fore st soils in the long term. The flora which established after waste add ition included many non-forest plants and indicated very good nitrogen supply in the soil. As a result of potential leaching of nitrate, was te applications to nutrient-rich or N saturated forest ecosystems may be an environmental risk.