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Title: Impacts of land-applying class B municipal biosolids on soil microbial activity and soil nutrient and metal concentrations

item Jin, Virginia
item Arnold, Jeffrey

Submitted to: Residuals and Biosolids Conference
Publication Type: Proceedings
Publication Acceptance Date: 10/23/2010
Publication Date: 5/6/2010
Citation: Jin, V.L., Witherington, E.M., Johnson, M., Haney, R.L., Arnold, J.G. 2010. Impacts of land-applying class B municipal biosolids on soil microbial activity and soil nutrient and metal concentrations. In: Proceedings of the Residuals and Biosolids Conference, May 23-26, 2010, Savannah, Georgia. Paper No. 20B. 2010 CDROM.

Interpretive Summary: Applying municipal biosolids to agricultural land is a common method for beneficially reusing and recycling waste. Municipal biosolids applications, however, could lead to the build-up of heavy metals in agricultural soils and negatively impact soil fertility and crop production. The effects of metal loading on soils can be evaluated by measuring soil microbial activities. Soil microbial activities are usually limited by the availability of energy sources, and the primary energy source for soil microorganisms is carbon (C) from organic matter. Although biosolids have higher concentrations of heavy metals, biosolids also are very high in organic matter content. In a study measuring soil microbial activity (i.e. respiration), microbial responses to greater C availability from biosolids applications appeared to compensate for potential negative impacts from heavy metal loading. Land-applying biosolids to agricultural soils, however, resulted in large increases in soil nitrogen and phosphorus concentrations. These results suggested that nutrient loss from biosolids-applied areas may be a more immediate risk to health and environmental quality via groundwater contamination and eutrophication. Future studies on movement of macronutrients and trace metals in bio-amendment systems will allow us to predict long-term effects and sustainability of various beneficial reuse practices.

Technical Abstract: Impacts of land-applying Class B biosolids on microbial activities and nutrient and metal concentrations in surface soils (0-10 cm) of coastal bermudagrass fields were measured during a 112-day incubation. Application rates were: control, 22, 45, and 67 dry Mg biosolids ha-1 y-1 for 8 years and 22 dry Mg ha-1 y-1 for 25 years (Austin, TX). As application rate increased, most nutrient and metal pools increased, though K, Se, Pb, and As decreased. Soil Al, Ni, Cu, Cd, and total P increased under long-term application. Cumulative CO2 production was greatest at the highest application rate, but did not differ at lower rates (P < 0.05). Net N mineralization and immobilization were greatest in the highest treatments (P < 0.05). Strong microbial response to greater C availability may have compensated for heavy metal loading impacts. Effects of biosolid land-application on inorganic N and P pools illustrate the importance of continued research.