Population trends of soil invertebrate macrofauna within a hedgerow intervropping in Embu, Kenya

The effects of land use practices on the soil invertebrate populations is well documented, but their potential as indicators of soil status is little understood. A study was undertaken to test the hypothesis that soil invertebrate macrofaunal communities vary in abundance and biomass at varying layers of soil 'within a hedgerow intercropping. The study was conducted over dry and wet spells during the long rainy season, at Embu in an ongoing on-station hedgerow intercropping agroforestry experiment started in the 1993 long rains. The macrofauna populations were monitored in soil monoliths (25 cm x 25 cm x 30 cm). Soil samples were collected from different locations within each plot at the start and at the end of each season to determine the soil physical and chemical parameters. Analyses of variance indicated highly significant differences among treatments, significant differences in soil depths whereas the interaction between treatments and soil depths was not significant. Faunal groups responded differently to different treatments. Macrofauna populations were significantly higher for treatments with Calliandra calothyrsus particularly when the treatment involved the incorporation of litter unlike with Leucaena leucocephala where the fauna showed significant response only whenever inorganic fertilizer was incorporated. Soil arthropods sampled within a hedgerow intercropping: termites, ants, beetles, centipedes, flies, spiders, mites and millipedes. Termites Were the most abundant constituting 78% of the total counts with a biomass of 21 glm2 followed by ants (13 % of the total counts with a biomass of 8 glm2), next was beetles which contributed 5% of the total faunal count but with the highest biomass of 56 glm2. The other faunal groups were found to be observed in relatively low numbers (centipedes 2%, 7 glm2; millipedes 1%, 5 glm2; spiders 1%, 4 glm2; mites and flies contributed less than one percent both in counts and biomass) constituting only 4% of the total faunal counts in the first season. Based on results of this study additions of Calliandra calothyrsus and Leucaena leucocephala have varied effect on faunal diversity in intensively cropped and nutrient depleted soils. In addition, continuous tillage can cause alterations in the population structure, elimination/reduction of key groups and species of soil fauna and in some cases low numbers or biomass. Thus much attention should be paid to their conservation. Foliage of Calliandra calothyrsus is a good green manure residue for soil nutrient management than that of Leucaena leucocephaLa. Resource-poor farmers who cannot afford inorganic fertilizers may be encouraged to plant CalLiandra calothyrsus in hedges or in contours and use this organic residue to improve the soil nutrient status.