The influence of soil fertility management practices on diversity and abundance of soil fauna in the central highlands of Kenya
The need for an increase in crop (particularly food) production to match the demand from an ever-increasing human population has led to intensive agriculture. This is usually associated with a high level of ecological disturbance. Soil fauna seem to play a key role in determining soil quality via mineralisation and the farmers already use presence of macrofauna as fertility indices yet their balance is likely to be upset by such disturbances. It is necessary to study their distribution in common farm management practices associated with intensive agriculture to determine which practices can be useful in increasing soil fertility and productivity sustainably. Presently, over 73% of the smallholder farmers in Kiambu District, Central Kenya are using crop manure, animal wastes and inorganic fertilizers to increase their farms' fertility and subsequent productivity. Disparity in these organic amendment and soil erosion control practices has resulted in a scenario whereby patches of productive/fertile and less-productive/degraded soils have developed and are conspicuously identifiable by majority of the farmers. This study was to find out if the organic resource management practices which farmers adopt in response to soil fertility decline, enhance the biodiversity and activity of soil fauna, some of which may serve as indicators of soil quality. Six small-scale farms were selected from members of Karura Catchment Committee in Kikuyu Division of Kiambu District. A series of 20 x 20 x 20cm soil monoliths were dug, macrofauna hand-sorted, identified and counted. In addition, some key microfauna/microorganisms (Bacteria, Fungi and Actinomyecetes) and mesofaunal groups (nematodes) were studied. The latter was done by plate dilution technique and the sieving/filtration respectively. Sampling was done as from May to December 2000. Results obtained pointed towards the fact that the farms that had no soil erosion control or soil fertility control (termed unproductive by farmers) were less species rich but more species-even (S=38 and J = 1.35323). Farms with both soil erosion control and organic amendments as a soil fertility control (termed productive by farmers) had a higher species richness of S = 47 and less evenness of J = 0.61614. The third category I had added as 'moderately productive' (had the least number of species (27) and a 'moderate' richness and evenness. The ratio of parasitic nematodes to non-parasitic nematodes was highest in the non-productive farms even though they had the least overall total count. Distribution of various microfauna groups differed in each farm with the lowest overall count being in the non-productive patches. Fungi density was highest in the degraded farms depicting a more acidic nature of the soils. Overall, these results pointed towards the fact the practice involving organic amendments incorporation and a soil erosion control involving agro forestry led to increase high faunal species, abundance and activity, rendering the farms more productive.