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ThesisItem Open Access Role of nematodes in soil health sustenance: relating their assemblages to soil types and cropping systems(UAS Dharwad, 2013) Kumari; S. LingarajuNematodes are functionally diverse. Most research on them is focused on plantparasitic nematodes that attack the roots of cultivated crops. Less attention has been given to nematodes that are not plant-feeders and play beneficial roles in soil environment. Therefore, the present study was taken up with the objective of determining nematode assemblages in different soil types and cropping patterns. Two agro-ecological Zones of Karnataka were selected (Zone III and IX), soil were vertisols and alfisols. The dominant cropping patterns were cotton, onion+chilli, paddy-paddy-paddy and paddy-paddy-paddy respectively. In addition to this, a field trial was taken was taken up at MARS, UAS Dharwad in two consecutive seasons, viz. Rabi-2011 and Kharif-2012 with major cropping pattern of this area (chickpea and soybean respectively) to know the influence of fertilizers and manures (singly and in combinations) on nematode assemblages. Also influence of soil physical and chemical properties were studied during the course of present investigation employing the soil samples which were collected during surveys and during field experimentation. Differences in nematode assemblages were observed during the study in different soil types with respect to trophic groups across different agro-ecological zones and during field study. MWC had positive correlation with nematode assemblages. BD on total nematode abundance was negative and showed significant positive correlation. Whereas pH showed negative correlation and effect of EC was almost negligible. Under field study, both FYM and vermicompost singly and in combination increased the numbers of bacterivores and fungivore nematodes and lowered that of plant parasitic nematodes. Different indices viz., NCR, NGR, H’, combined maturity index (MI) were calculated - a slight change across the sampling period was noticed. Results suggested that a bacterial decomposer pathway dominated, mediated by bacterivorous nematodes. In a microcosm experiment it was observed that there was increase in total available nitrogen from 12 to 14 (kg/ha) over control in presence of bacterivorous nematodes.