Location: Sugarcane ResearchTitle: Changes in microbial properties after manure, lime, and bentonite application to a heavy metal-contaminated mine waste) Author
Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2011
Publication Date: 4/18/2011
Citation: Baker, L.R., White Jr, P.M., Pierzynski, G.M. 2011. Changes in microbial properties after manure, lime, and bentonite application to a heavy metal-contaminated mine waste. Applied Soil Ecology. 48(2011):1-10. Interpretive Summary: One proposed method for containing lead and zinc contaminated mine wastes on site is to apply large quantities of organic matter, such as compost or manure. These materials promote microbial development and the establishment of a vegetative cover on the site. Our objective was to determine if large applications of compost (> 200 Mg ha-1) will support increased soil microbial activity, increase nutrient cycling, and limit the availability of heavy metal contaminants which are toxic to soil microbes and young plants. We used beef manure compost applied at two different levels (45 and 269 Mg ha-1) with and without lime and clay to investigate the changes in microbial community structure and function. The clay was included because it is occasionally used to create pelletized composts. Switchgrass (Panicum virgatum) was seeded into plots to establish a vegetative cover. Compost additions increased soil carbon, nitrogen, phosphorous, and potassium contents along with soil pH values. Enzyme activities associated with high nutrient cycling by microbes increased with compost additions. The compost also reduced the amount of bioavailable heavy metals in the waste/soil material. Bentonite and lime had little impact on variables measured, however, in areas with very low pH lime is recommended. Overall results indicate that large amounts of composted beef manure can successfully “jump-start” nutrient cycling by native soil microbes and ultimately improve overall soil health. An increased nutrient supply should aid in sustaining vegetation at such sites, which helps to prevent runoff and/or movement of heavy metal contaminants to non-contaminated areas.
Technical Abstract: One proposed method for stabilizing lead (Pb) and zinc (Zn) contaminated mine wastes is to apply large quantities of organic matter in order to improve soil physical, chemical, and biological characteristics, which should stimulate nutrient cycling, reduce metal availability, and facilitate vegetation establishment. The objective was to determine if large applications of compost (> 200 Mg ha-1) will support increased microbial activity over time. We used beef manure compost applied at two different levels (45 and 269 Mg ha-1) with and without lime and bentonite to investigate the changes in microbial community structure and function. Switchgrass (Panicum virgatum) was seeded into plots to establish a vegetative cover. Compost additions significantly changed carbon (C), nitrogen (N), phosphorous (P), and potassium (K) contents along with pH values. Enzyme activities and microbial biomass measurements were used to monitor nutrient cycles upon amendment addition. After five months the high compost, high compost + lime, and high compost + lime + bentonite treatments had significantly higher arylsulfatase and phosphatase activities compared to all other treatments. The high compost treatment had a significantly increased ß-glucosidase activity and also more microbial biomass C, while other measurements were more variable. Increases in microbial activities were significantly related to increases in total C, P, and estimated available water, while negative relationships existed with electrical conductivity and bioavailable Zn. Phospholipid fatty acid analysis (PLFA) was used to assess changes in microbial community structure. Microbial community characteristics (Mole % of PLFA) were not strongly impacted by compost. However, principal components analysis (PCA) of PLFA profiles shows that treatments containing a high compost level caused a significant shift in microbial community composition. Gram-positive bacteria, Gram-negative bacteria, and fungal biomass as determined by PLFA were significantly higher in the 269 Mg ha-1 treatment than in the no compost control and 45 Mg ha-1 treatments. Results suggest that an organic matter addition ranging between 45 and 269 Mg ha-1 is needed to support and sustain (~ 2 years) microbial activity and biomass in contaminated mine waste materials.