Evaluation of cocomposted coal fly ash on dynamics of microbial populations and heavy metal uptake

Vicia faba, in a pot experiment with sandy and clayey soils under greenhous e conditions, was checked for growth response to different amendments with coal alkaline fly ash or cocomposted fly ash mixed with lignocellulosic res idues. Soil microbial populations, pH and electrical conductivity as well a s heavy metal uptake by plants were monitored. At rates of five and ten per cent (on a dry matter basis) in both soils, neither fly ash alone nor cocom posted fly ash exerted any negative effect. Plant biomass production was no t influenced in either clayey or sandy soil. Alkaline fly ash did not promo te microbial growth when applied alone to the soils. However, cocomposted f ly ash generally increased bacterial and actinomycetes counts in both soils . Fungi were not affected by ash. Due to the increase of soil pH by alkalin e fly ash or cocomposted fly ash, plant uptake of heavy metals was depresse d in the sandy soil. Heavy metal mobility did not cause change in the claye y soil where a high buffering capacity mitigated the effects of fly ash ame ndments.