CO2 evolution and enzyme activities (dehydrogenase, protease and amylase) of fly ash amended soil in the presence and absence of earthworms (Drawida willsi Michaelsen) under laboratory conditions

The CO, evolution and dehydrogenase, protease and amylase activities of fly ash amended soil (Orissa, India) in the presence and absence of earthworms were investigated under laboratory conditions for 2 months at 50% water-holding capacity (WHC) and 25 +/- 2 degreesC temperature. A toxicity test of different age groups (juvenile, immature and adult) of Drawida willsi earthworms, dominant (>80% both in number and biomass) in crop fields of India, was conducted for 14 days at different concentrations of fly ash amended soil. On the basis of the results of the toxicity test, seven concentrations of fly ash amended soil were chosen (0, 2.5, 5, 10, 15, 25 and 50%; w/w) to study the CO(2) evolution and enzyme activities in the presence and absence of D. willsi. The results demonstrated little or no inhibition of soil respiration and enzyme activities up to 2.5% fly ash amendment. With further addition of fly ash, all the above activities were significantly decreased. On the other hand, significant stimulation of soil respiration and microbial activities were observed up to 5% fly ash amendment when the soils contained earthworms. This may be due to increased microbial activity induced by substrates that are produced by the earthworms. Co-application of fly ash and earthworms at lower doses can thus be considered to stimulate soil biological activity and thereby improve nutrient cycling in acidic soil. (C) 2003 Elsevier B.V. All rights reserved.