Submitted to: Handbook of Soil Conditioners
Publication Type: Book / Chapter
Publication Acceptance Date: 4/15/1997
Publication Date: N/A
Interpretive Summary: Municipal sewage sludge and some other organic residues from industrial sources are desirable materials for soil amendments. These materials can better soil quality by improving physical, chemical and biological properties. Many soils will benefit from the application of sludge because of the organic matter it contains. The increase in crop yields with applications of sludge greater than 5 tons per acre is related to the supply of nitrogen, phosphorus and potassium where these nutrient elements were low in the soils. Trace metals in sludge remain an important concern because they might be incorporated into plants or animals through the food chain. The trace metal cadmium has been shown to be accumulated in plants and earthworms, while other trace metals were somewhat less concentrated. Soil microbe populations are affected in different ways. Total microbial populations remain at a balanced level after 2 years of sludge treatments, while some specific groups of soil microorganisms such as nitrogen- fixing bacteria are increased. Application of sewage sludge to agricultural lands has beneficial effects at low application rates of 1 to 2 tons per acre, while potential environmental hazards due to trace metal increases in soils or plants must be continuously observed. Results of this research will be used by extension specialists and others with environmental interests to provide information to farmers and researchers who benefit from application of organic wastes to land.
Technical Abstract: Biosolids (sludges) obtained from municipal and industrial sources have properties which make them desirable amendments for soils. These amendments can improve soil physical, chemical and biological properties by the additions of organic matter (OM), nitrogen (N), phosphorus (P), and potassium (K), as well as trace metals to soils. However, Practical Limits of Application (PLA) rates must be observed due to environmental and plant growth concerns. Organic matter comprises a large fraction of a biosolid and affects the soil bulk density, field capacity and cation exchange capacity. For most soils, the need for N in production systems has placed a PLA in the order of 1 to 2 Mg ha**-1 for a beneficial effect. Of the current guidelines, the economic approach which measures the amounts of metals removed from agricultural lands and the gains from application of biosolids provides an initial estimate of the PLA. The populations of soil bacteria, actinomycetes, and fungi can be stabilized after two years. Effects on specific populations showed changes for nitrifiers and antibiotic-resistant microorganisms in soils. The trace metal Cd was highly concentrated in earthworms, whereas Cu was somewhat less concentrated. The metal concentrations for Zn, Pb, and Ni varied with different case studies. Application of biosolids sludge to agricultural lands has beneficial effects at low application rates, while potential environmental hazards due to trace metal increases in soils or plants must be continuously observed.