ABSTRACT
I. INTRODUCTION Soils as a dynamic system produced by microbial and faunal activities or physicochemical reactions are crucial to the functioning of a terrestrial eco system. Although soils represent only a thin layer of the earth surface, they are the habitat of many microbial and faunal species which play an important role as catalysts in the global C-, N-, P-, and S-cycles. Products of organic matter cycling in soils interact with the surface and ground waters as well as with the atmo sphere. Soil organic and clay components are important nutrient reservoirs and the basis of agricultural production. Crop production, waste water, and compost plants, as well as livestock farms produpe a variety of organic residues, bio composts, sewage sludges, and animal wastes. All are rich in nutrients and con tain some heavy metals or hazardous organic material (Vetter and Steffens, 1986; Unken, 1987; VDLUFA, 1990; Fruchtenicht et al., 1993; Poletschny, 1994a, 1994b). Highly productive German farms produce in average about 4000 kg organic residues ha-1 (DM) annually, which have to be recycled (Fruchtenicht et al., 1993). Of German sewage sludges approximately 20%-25% are recycled as fertilizers. The rest is composted (2%-3%), burned (ca. 10%), or dumped
in landfills (ca. 60%-65%) (Statistisches Jahrbuch, 1992; Umweltbundesamt, 1992). Furthermore, in Germany about 5 x 106 tons of biocomposts are produced annually (Poletschny, 1994b). In Germany alone plant residues, animal wastes, sewage, and biocomposts are applied as fertilizers to about 70 different soil types, which are differentiated by their surface chemical, mineralogical features, organic composition, and texture (specific soil fertility) (Kuntze, 1991). Food or indus trial crops, vegetables, grasses, or other fodder plants, bushes, and trees profit from the soil-specific fertility. Besides plants about 105-109 bacteria, 104-107 fungilike growing bacteria (actinomyces), 103-106 fungi, 103-105 algae, and 103-107 protozoa per gram of dry soil as well as about 102-106 nematodes, enchytraeides, collemboles, and mites; 103-105 individuals of different macrofaunal groups; and 5-300 earthworms per square meter inhabit the soil water films, pore spaces, and surfaces (Ottow, 1985) (see Chapters 3-9). Fertilization during the last 60 years not only increased the amount of harvest residues but improved soil fertility three or four times (Isermann, 1993), and soil biological communities, making nutrients from organic material available for crop produc tion, adapted to the new conditions. More soil fertility means more fodder and food, more animals and human beings, and consequently more organic fertilizers. In addition altered animal husbandry and human life-style lead to more fluid than solid wastes, and fodder, and food imports increase the regional production of sewage and animal wastes by another 20% (Vetter and Steffens, 1986). Farmers, making nutrients of plant residues, night soils, animal wastes, and sewage sludges available for crop production, developed a variety of organic farming systems in the last decades (Lampkin, 1990). Imbalanced nutrient inputs cause eutrophica tion in the adjacent biotops (excessive growth of algae, phyto-and zooplankton; change of species; mass growth of macrophytes; expansion of macrobenthos fauna; and changed fish fauna), impair the groundwaters or drinking waters, stress the atmosphere, and mean finally a risk for human health (Isermann, 1990a, b; Arbeitskreis, 1991; Walsh et al., 1991; Isermann, 1993).
