Investigating the effects of chemical fertilizers on population variations of different species of earthworms

Earthworms have been used for many toxicity assay and environmental assessments because of the remarkable role they play in the biological, chemical and physical processes of the soil. The purpose of this study was to investigate the impact of chemical fertilizers on the density of earthworms in the soil of an orchard. One square meter area was considered as experimental plot. Seven different types of fertilizers including Urea, Ammonium sulfate (AS), Diammonium phosphate (DAP), Solupotas, NPK (15-5-25), (NPK+OM) and organic manure (OM) as experimental treatments were studied, based on the soil test. Abundance of worms were evaluated in two stages of time and in 2 depths of 0-20 and 20-40 cm of soil. In the first stage, 20 days after the addition of fertilizers, and in the second stage, 60 days after fertilization, earthworms were sampled and their number changes were measured. Treatments were applied in three replications and the data were analyzed using one-way ANOVA (using the GLM process) by SPSS software. The results of the means comparison showed that on the 20th day, at 0-20 cm soil depth, E. fetida species abundance was decreased significantly in AS and Urea treatments compared to the control plot (p˂0.05). From epigeic group, D. hortensis species showed more compatibility and its population in AS treatment was more than that of Urea treatment. Results also showed that the anecic L. terrestris, had a greater tolerance to chemical fertilizers compared to the A. Longa species.