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The soil nematode food web structure under a potato crop compared to a forest control treatment was investigated for 10 months. All nematode functional guilds were recovered from both treatments. Higher populations of enrichment nematodes (bacterivores and fungivores) were recovered in the potato plots and this is attributed to possible higher amounts of organic matter in the crop plots as compared to the forest control. For the pest suppression species, higher populations of carnivorous nematodes were recorded in the forest samples, while higher populations of the omnivorous nematodes were recorded in the potato plots. It will therefore seem that while the environmental response of predatory (carnivorous) nematodes is linked to physical perturbation, food sources are a more important factor in the environmental response of the omnivorous nematodes. Whereas the plant-feeding species of the Pl 3 class were significantly higher in the crop plots, the Pl 5 plant species were significantly higher in the forest control samples. These differences are attributed to host specificity. Overall, the plant-feeding nematodes dominated (9 families, 14 genera, 35.73 % total biomass contribution), followed by the enrichment nematodes (8 families, 12 genera, 33.53% total biomass), and then the pest suppression species (9 families, 19 genera, 30.76% total biomass). Based on these results plant-parasitic nematodes of the Pl 3 cp class particularly Helicotylenchus mucronatus, Rotylenchus buxophilus, and Meloidogyne microcephala, are considered a potential threat to potato production in the study area.

The effects of crop rotation sequences and combinations on soil nematode populations were investigated. Tillage versus non-tillage treatments were applied to crop rotation sequences dominated by flooded rice in a split plot design. The rotated crops were rice, soybean, and corn, including a fallow for a total of eight rotation treatments. All nematode feeding groups were recovered i.e bacterial feeding-, fungal feeding-, plant feeding-, carnivorous-, and omnivorous-nematodes. A total of 24 nematode genera in 20 families were identified and categorized into their respective trophic groups and colonizer persister (cp) values. All rotations that included soybean significantly (P<0.05) or numerically increased soil nematode populations, irrespective of trophic groups, while all rotations that included rice and corn, had a nematode reductive effect. No-tillage plots recorded significantly higher populations of the predatory nematodes. The effectiveness of a rotation sequence depends primarily on the crop species and secondarily on soil conditions e.g anaerobic.

Numbers of nematode species, juveniles, females and males in earthworm casts and in adjacent soils were studied in fallow (FL) and in cultivated lands (CL). In the FL each cast had an average of 5.6 different species of nematodes, while a soil sample of equal weight to the cast and within a 10 cm radius of the cast averaged 2.5 species. The difference between these means was highly significant. In the CL there were 4.7 species/cast and 2.9 species/soil sample. The difference between these two means was also highly significant.A total of 16 plant parasitic species, five omnivorous, two predacious and eight free-living nematode species were observed in the casts and in the adjacent soils of both FL and CL. The results partially contradicted the widely held view that earthworm casts are beneficial because the casts harboured numerous plant parasitic nematodes.