Comparison of the Population of Soil-Inhabiting Nematoda in The Context of Pesticide Application with an Observation on Their Trophic Groups

Abstract

Soil-inhabiting Nematodes are agriculturally important for significant loss of crop production as well as for their beneficial role in soil ecosystem. During a visit to Bali Island of Indian Sundarbans, West Bengal, India, few soil samples were collected from agricultural fields. As reported by the villagers, some fields were applied with pesticides like Furadon (carbofuran 3% g) and Phorate (Phorate 10% g organophosphate) and some were without any pesticide. Both of these pesticides have nematicidal effects besides being contact and systemic insecticide. The collected soil samples were processed by Cobb’s Sieving and Decantation Method followed by modified Baermann Funnel Technique to extract the nematodes. The populations of nematodes were counted with the help of a counting dish and a hand tally counting machine under a stereo zoom microscope following standard method. The soils applied with pesticides, collected from cauliflower and tomato fields, showed a lesser population count of 26 and 98 nematodes respectively in 250 gm. of soil for each of the samples, whereas the population count for the soils without pesticides from vegetable and paddy fields were 293 and 625 nematodes respectively in the same quantity of soils. The nematodes were identified up to the generic level and presence of twelve genera was observed which indicates an idea about their trophic groups in the soil micro-habitat of agro-ecosystem being associated with the mangrove ecosystem (‘ecotone’ of terrestrial and marine ecosystem) of Sundarbans. So this observation can be considered as various trophic levels of nematodes in an ‘ecotone’. Soils with the pesticides showed only two trophic groups (omnivorous and predatory-omnivore), whereas soil without pesticides revealed four trophic groups (plant and hyphal feeder, omnivorous, bacterial feeder and predatory) of nematodes. The difference in population in different soils was statistically analyzed to show the relation between the nematode population in the soil applied with pesticides and without pesticides.