Nematode Composition and Soil Conditions in Plots under a Wheat Crop in Colfax, Washington State

Plant parasitic nematodes have been identified as a major problem to wheat (Triticum aestivum L.) production in the Pacific Northwest (PNW) states of the USA. Nematicide control of these parasites has been successful. We were, however, interested in understanding how the soil nematode-nematode interactions and the nematode-host plant interactions affect nematode populations of different feeding groups and how the soil nematode composition could be used to elucidate soil conditions in a winter wheat crop. Our results revealed that the ratio of the plant-parasite index (PPI) to the maturity index (MI = free-living nematodes) was high, meaning we had higher populations of the herbivorous nematodes than all of the other feeding groups combined. The low populations of the free-living nematodes meant little or no nitrogen mineralization by the bacterivorous and fungivorous nematodes, and also a lack of meaningful predation of the plant-parasitic nematodes by the pest suppressive species i.e omnivores and carnivores. The high plant-parasitic nematode populations and low populations of the free-living nematodes may have also interfered with nutrient uptake by the plants and resulted in stressed soils in the plots studied. Based on our results, farming methods that will reverse the PPI/MI ratio will be a natural and ecologically friendly way of reducing populations of the parasitic nematodes in the wheat plots e.g. rotations and soil amendments. During the different sampling periods, the soil conditions changed from basal, to enriched, and then maturing, based on the nematode composition. Thus the soil nematode composition can be used for the biomonitoring of soil conditions in wheat plots.