Dose-related effect of fly ash on edaphic properties in laterite cropland soil

Short-term laboratory and field studies showed dose-based effect of coal fly ash on chemical and microbial properties of laterite cropland soil. Sandy loam soil mixed with farmyard manure (10% w/w) and amended with fly ash at 5%, 10%, 20%, 40% w/w (50–400 t ha−1) was incubated in the laboratory and added to field plots. The pH, EC, PO4, Ca and Na of soil increased with dose and time, but OC, NO3 and K decreased. There was temporary inhibition of bacteria, fungi and actinomycetes populations at 5% and 10% doses, but 20% and 40% were harmful. Activities of major soil enzymes declined at higher doses. Amylase, cellulase and invertase recovered in 5% and 10%, these doses did not affect dehydrogenase but benefited phosphatase and arylsulphatase activities. The above assessments showed that up to 100 t ha−1 fly ash is apparently safe to microbial characteristics of tropical red laterite soil.