A comparative study on lethal concentration (LC<sub>50</sub>) of urea and diammonium phosphate to earthworms, <i>Eisenia fetida</i>

In managed agro-ecosystems, urea and diammonium phosphate (DAP) are widely used artificially synthesized fertilizers for crops as nitrogenous supplements. Overdose of chemical fertilizer poses a threat to various soil-dwelling microorganisms and earthworms, too. The present study aimed to determine the detrimental effect of nitrogen supplements (urea and diammonium phosphate) on earthworms (Eisenia fetida). To calculate LC50 for urea and DAP, the experimental set-up was maintained as per the recommendations of Organization for Economic Co-operation and Development (OECD) guidelines number 207 for testing the chemicals. Ten adult gut-cleaned earthworms were inoculated in artificial soil mixed with testing chemicals. Five sets of replica with each test chemical in different concentrations were used for 14 days for better estimation of mortality. Mortality was the endpoint. Median lethal concentration (LC50) of urea and DAP was calculated through Finney Probit regression analysis. At 300 mg/kg concentration of urea, earthworms had no mortality and at 1000 mg/kg there was ≤50% mortality. The LC50 value for urea was 862.126 mg urea per kg of the soil at 95% confidence interval and at 500 mg/kg concentration of DAP, there was no mortality of earthworms; at 2400 mg/kg, there was ≤50% mortality. The LC50 value for DAP was 2098.69 mg DAP per kg of the soil at 95% confidence interval. Comprehending the LC50 value is crucial when determining an appropriate application rate of chemical fertilizers in an agricultural setting to avoid damaging earthworm populations, which are vital to the soil's fertility and overall health. More specifically, the diversity and population of earthworms indicate the health of the soil and evolve into a cost-effective component of the agro-managed ecosystem.