Submitted to: Managing the Risks of Nitrates to Humans and the Environment
Publication Type: Book / Chapter
Publication Acceptance Date: 9/1/1998
Publication Date: N/A
Interpretive Summary: The long-term study of the Rosemount, Minnesota watershed is a landmark example of a detailed environmental and agronomic analysis of sewage sludge application to land. The value of sludge as a fertilizer substitute was established for corn and grass crops. Yields on sludge-treated areas were slightly better than those on fertilized control areas. Grass was more efficient than corn in removing nutrients supplied in the sludge. From a water quality viewpoint, the Rosemount watershed study showed that sludge application can be conducted in an environmentally safe fashion. Surface water quality was protected when adequate soil erosion measures were taken at the site. It was shown that fertilizer and sludge application rates that supplied nitrogen in excess of crop uptake, affected the nitrate concentration of near-surface water. This issue emphasizes the need for proper management of all nutrient sources in agriculture to protect ground water resources and to prevent health risks to humans and animals. The Apple Valley, Minnesota wastewater effluent study showed that increases in nitrogen applications from effluent irrigation produced larger increases in soil water nitrate concentrations under corn than under forages. Nitrate concentrations in soil water were considerably higher under the fertilized control than for the effluent irrigation under both crops. The high nitrate values from fertilizer draw attention to potential health risks from nitrogen applications which exceed crop requirements. Municipal wastewater effluent can be successfully renovated by slow-rate irrigation land treatment systems. Land application of both sewage sludge and wastewater will benefit municipalities, farmers, and the general public.
Technical Abstract: Research was initiated in 1973 at St. Paul, Minnesota, with objectives to develop efficient, practical, and environmentally safe methods for utilizing sewage wastes on land in harmony with agricultural usage. Applications of municipal sewage sludge and/or wastewater effluent were studied. Liquid digested sewage sludges from several wastewater treatment plants were applied to a 16-ha terraced watershed cropped to corn and reed canarygrass. The sludge was transported to the site by tank truck, stored in lagoons, and spread by combinations of traveling gun and subsurface injection. Sludge was applied to the corn areas for 20 years (total of 68 cm, 224 Mg/ha solids, and 9460 kg/ha total N) and to the reed canarygrass areas for 12 years (total of 96 cm, 173 Mg/ha solids, and 10,040 kg/ha total N). Crop yields were high with normal plant tissue concentrations of N, P, and K. Analysis of water samples from runoff, soil, and ground water showed no movement of potentially polluting materials out of the watershed via surface runoff or leaching. Wastewater effluent was sprinkled onto a 2- ha area containing maize and eight forage species for a four-year period at about 5 and 10 cm/wk (total of 120 to 280 cm/yr and 260 to 680 kg N/ha/yr). Tile drainage, ground and soil water, soils, and crops were analyzed for N, P, K, and trace metals. Corn and forage grasses produced high yields (average of 13.4 and 11.1 Mg/ha for corn and reed canarygrass, respectively). Removal of N and P from effluent by the combination of crop uptake and soil sorption was satisfactory. No increase in trace metal concentrations was detected in either the water or crops. Special manage- ment of the crop was important for maintaining adequate infiltration rates, for producing high yields of dry matter, and for maximum removal of N.