Effect of fly ash application on soil microbial response and heavy metal accumulation in soil and rice plant

Abstract

Fly ash(FA),a byproduct of coal combustion in thermal power plants, has been considered as a problematic solid waste and its safe disposal is a cause of concern. Several studies proposed that FA can be used as a soil additive; however its effect on microbial response, soil enzymatic activities and heavy metal accumulation in soil and grain of rice (cv.Naveen) to fly ash(FA) application was studied in a pot experiment during dry season 2011 in an Inceptisol. Fly ash was applied at a rate of zero percent (FS), five percent (FA5), ten percent (FA10), twenty percent (FA20), 40 percent (FA40) and 100 percent (FA100) on soil volume basis with nitrogen (N), phosphorus (P) and potassium (K) (40:20:20 mg N:P:K kg-1 soil) with six replications. Heavy metals contents in soil and plant parts were analysed after harvest of crop. On the other hand, microbial population and soil enzymatic activities were analysed at panicle initiation stage (PI, 65 days after transplanting) of rice. There was no significant change in the concentration of zinc(Zn), iron(Fe), copper(Cu), manganese(Mn), cadmium(Cd) and chromium(Cr) with application of fly ash upto FA10. However, atFA100 there was significant increase of all metals concentration in soil than other treatments. Microorganisms differed in their response to the rate of FA application. Population of both fungi and actinomycetes decreased with the application of fly ash, while aerobic heterotrophic bacterial population did not change significantly upto FA40. On the other hand, total microbial activity measured in terms of Fluoresceindiacetate (FDA) assay, and denitrifiers showed an increased trend upto FA40. However, activities of both alkaline and acid phosphatase were decreased with the application of FA. Application of FA at lower levels (ten to twenty percent on soil volume basis) in soil enhanced micronutrients content, microbial activities and cropyield.