Lethal effect of urea on soil biota : a laboratory study on earthworm (Drawida willsi)
Journal Title: Journal of Biodiversity and Environmental Sciences (JBES) - Year 2014, Vol 4, Issue 6
Abstract
The lethal effect of agrochemicals especially the pesticides on the soil ecosystem are well studied. Contrary to this, very few studies were conducted on the impact of fertilizer on the soil health. Urea among the fertilizers has been widely used in the agricultural field to boost up production. But only few studies were conducted to find out its toxic effect on soil ecosystem. However none of the study was undertaken on earthworm Drawida willsi Michaelsen as a test animal which constitutes the dominant earthworm in crop fields of India. Therefore an experiment was conducted to find out the eco-toxicity of urea on D. willsi. For this, soil and earthworm were collected from such agricultural field where there had no record of input of agrochemicals. Different concentrations of urea were prepared in dilution of water which then added to the experiment sets. Ten healthy gut evacuated earthworms of each age group (juvenile, immature, adult) were added to five replicates (polythene packets) for each concentration of fertilizer. On the other hand, the control group was given only water, and same numbers of earthworms were added with each age group. The experiment was maintained at 20±2g% soil moisture and 25±2°C soil temperature. Earthworm deaths were recorded and Finney’s probit method was followed to calculate 96h LC50 values. Study found no mortality of juvenile, immature and adult D. willsi worms at the dose of 100, 200 and 200 mg urea /kg dry soil respectively. So, all the age groups of earthworm could tolerate up to 100 mg urea per kg of dry soil. At 800 mg urea /kg of dry soil 100%, 76% and 52% of mortality for juvenile, immature and adult earthworm was observed. Therefore, at this dose all the age groups of earthworms are in danger of extinction. The 96 h LC50 values with their 95% confidence limits for juvenile, immature and adult worms were 422.7 (422.66- 422.74), 547.02 (546.96-547.08) and 827.9 (827.89-827.90) mg/kg respectively which is much more than the recommended agricultural doses of urea (79.04 mg/kg soil). Though the recommended dose of urea fertilizer is safe so far as the mortality is concerned, there must be some sub-lethal effect on earthworm like growth, reproduction and metabolism. Even the use of urea at higher dose may cause severe mortality of earthworm. So proper care should be taken on doses during use of urea in the agricultural field.
Authors and Affiliations
Anindita Bhattacharya, Sanjat Kumar Sahu
Keywords
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