POTENTIAL USE OF PLANT RESIDUE WASTES IN FORESTS OF NORTHWESTERN GERMANY

Increasing amounts of waste and limited space for its deposition require 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 incubation, and by field experimentation at two sites with contrasting soil properties. The wastes used were a fresh and shredded material and a mature compost, both from plant residues, and were nutrient rich with high contents of bases and low concentrations of heavy metals. Long-term laboratory incubation showed no difference in total N mineralization between fresh organic waste, mature organic compost and beech litter. The nitrification rates in the organic wastes were higher, however. Carbon dioxide evolution was higher from fresh organic waste, and lower from mature organic compost than for beech litter. Neither liming nor addition of different soils, which served as inocula, significantly influenced N or C mineralization in wastes. Of total potassium in fresh organic waste 80% was released during a 67 day incubation period. Seepage water samples from an acid brown earth and a Terra fusca-Rendzina site showed negligible differences between concentrations of most most elements for waste application and control plots. However, in both soils potassium and chloride concentrations were highest under mature compost. After 21 months, the pH of humus and mineral soil below waste layers had not increased. The basicity of waste will deacidify acid forest soils in the long term. The flora which established after waste addition included many non-forest plants and indicated very good nitrogen supply in the soil. As a result of potential leaching of nitrate, waste applications to nutrient-rich or N saturated forest ecosystems may be an environmental risk.