Nematode response to soil organic amendments in a semi-arid region under soybean (Glycine max), Naivasha, Kenya.

Abstract

Agricultural production within the smallholder farming sector of East Africa is constrained by numerous factors including parasitic nematodes. Existing control measures involving applications of chemical nematicides are not viable in the medium to long term due to environmental concerns relating to toxic residues. There is therefore a need to develop alternative control options for integrated parasitic nematode management that will promote soil eco health and reduce parasitc nematode densities. This study evaluated population changes of soil nematodes, root galling and changes in soil properties following addition of soil organic amendments in a semi-arid region under soybean cultivation. Biochar, Vermicompost and Mycorrhizae were incorporated as organic amendments and applied as single or combined treatments using a randomised block design. Paecilomyces lilacinus a nematophagous fungus was used as a positive control. Nematodes were extracted from the soil using the modified Baermann extraction tray technique, identified to genera level then grouped into their trophic groups as herbivores, fungivores, predators or bacteriovores. Results at flowering stage showed no significant difference (P>0.05) between the treatments on predating, bacterivorous and fungivorous nematode populations. Conversely, Biochar and the untreated plots had significant high populations of parasitic nematodes (P<0.05).The combination of Biochar and Mycorrhizae application recorded significantly lower galling index at flowering between the treatments. At the end of the trial there were no significant differences in trophic group populations, however Biochar plots had a 40% reduction in parasitic nematode populations as compared to flowering stage populations. Vermicompost treated plots recorded significantly higher galling index and elevated amounts of extractable Phosphorous. Biochar is a viable option for use in integrated parasitic nematode control because of its potential to increase yields and reduce parasitic nematodes as was observed in this study, however more studies are needed to evaluate effects of Biochar and its interactions with Mycorrhizae on parasitic nematode densities due to their combined potential to lower parasitic nematode populations as was also observed. Paecilomyces lilacinus still remains a viable treatment for the control of plant parasitic nematodes.