Impacts of Land-applying Class B Municipal Biosolids on Soil Microbial Activity and Soil Nutrient and Metal Concentrations

Impacts of land-applying Class B biosolids on microbial activities and nutrient and metal concentrations in surface soils (0-10 cm) of coastal Bermuda grass 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.