SEASONAL VARIATIONS OF NEMATODE ASSEMBLAGES AND DIVERSITY ON SELECTED SOIL GROUPS IN KENYA: VERTISOLS, CAMBISOLS AND ARENOSOLS

Abstract

Background. Soil health assessment has been based on narrow disciplinary approaches that overlook the multiple and interacting biological processes that are the basis of sustainable crop productivity. Objective. Determine the influence of seasonal variations in nematode assemblages in different soil groups, sites and disturbance levels as an indicator of soil health. Methodology. Sampling was done in areas characterized by small scale subsistence agriculture in Kenyan Northern sites and Southern sites over three distinct seasons. The sampling points included disturbed (tilled) and the adjoining undisturbed (untilled) soils within three soil groups, namely Vertisols, Cambisols and Arenosols. Nematodes were extracted using the centrifugal-floatation technique, enumerated and assigned to their respective trophic groups. Results. Total nematode abundance in the three seasons varied significantly (p ≤ 0.05) with a mean of 68, 93 and 52 nematodes in 200 cm3 of soil in seasons I, II and III, respectively. Nematodes abundance in the undisturbed soils was significantly higher (98) compared to the disturbed soils (62) nematodes per 200 cm3). Mean abundance of nematodes was highest in Cambisols. In addition, nematode abundances, in all trophic levels across the three seasons, were significantly higher (p≤0.05) in the northern compared to the southern sites. Bacterivores (28%) had the highest percentage frequency of detection followed by herbivores (27%) and fungivores (21%) while omnivores (11%) had the least. Implications. Nematode communities do respond variably to different soil groups and seasonal changes. Conclusion.  Nematodes can therefore be utilized as viable bio-indicators of soil health and quality.