versión On-line ISSN 1870-0462
Trop. subtrop. agroecosyt vol.13 no.1 Mérida ene. 2011
Artículos de investigación
Effect of integrated soil fertility management interventions on the abundance and diversity of soil Collembola in Embu and Taita Districts, Kenya
Efecto del manejo integrado de la fertilidad del suelo sobre la abundancia y diversidad de Collembola en suelos de los Distritos de Embu y Taita, Kenia
J. J. Muturi1*, J. P. Mbugi1, J. M. Mueke1, J. Lagerlöf2, J. K. Mung'atu3, G. Nyamasyo4 and M. Gikungu5
1 Department of Zoological Sciences, Kenyatta University, P.O. Box 43844-00100, Nairobi, Kenya *Corresponding author Email: firstname.lastname@example.org
2 Swedish University of Agricultural Sciences, Department of Ecology, P. O. Box 7044, SE-75007 Uppsala, Sweden
3 Department of Statistics and Actuarial Science, Jomo Kenyatta University of Agriculture and Technology P. O. Box 62000-00200, Nairobi, Kenya
4 School of Biological Sciences, University of Nairobi, P.O. Box 30197- 00100, Nairobi, Kenya
5 National Museums of Kenya P.O. Box 40658-00100, Nairobi, Kenya.
Submitted May 6, 2010
Accepted June 9, 2010
Revised received November 16, 2010
The study aimed at identifying soil fertility management practices that promote the Collembola population, diversity and survival in the soil. Soil samples were randomly collected from on farm plots amended with: 1-Mavuno ((Ma)-is a compound fertilizer containing 26% Potassium, 10% Nitrogen, 10% Calcium, 4% Sulphur, 4% Magnesium and trace elements like Zinc, Copper, Boron, Molybdenum and Manganese)), 2-Manure (Mn), 3-Trichoderna (Tr) inoculant (is a soil and compost-borne antagonistic fungus used as biological control agent against plant fungal diseases), 4-Farmers practice ((FP) where Tripple Super Phosphate (T.S.P.) and Calcium Ammonium Nitrate (C.A.N.) fertilizers are applied in the soil in mixed form), 5-Tripple Super Phosphate (T.S.P.), 6-Calcium Ammonium Nitrate (C.A.N.). These treatments were compared with 7-Control (Co) (where soil fertility management interventions where not applied). Soil Collembola were extracted using dynamic behavioural modified Berlese funnel and identified to the genus level. Occurrence of Collembola was significantly affected by soil fertility amendments in both Taita and Embu study sites (P<0.05). Twenty two genera of soil dwelling Collembola were recorded, with control and organic manure treated plots recording high diversity with a Shannon 1.86 in Embu and a Shannon 2.09 in Taita, respectively. There was significant difference (P<0.05) of seasonality on soil Collembola occurrence at both Embu and Taita. Application of cow manure and addition of Trichoderma inoculants promoted the soil Collembola. The study has demonstrated that application of organic amendments encouraged the soil Collembola while inorganic fertilizers negatively impacted on these soil organisms.
Key words: Soil Collembola; Trichoderma; Organic manure and inorganic fertilizers.
Low soil fertility is a major constraint affecting agricultural production in sub-Saharan Africa, leading to decline in per capita food production (Mokwunye et al., 1996; Sanchez et al, 1997). Soil fertility degradation is "alteration to all aspects of the natural (or biophysical) environment by human actions leading to detrimental effects on vegetation, soils, landform, water and ecosystems" (Swift and Shepherd, 2007). Loss of vegetation leads to soil degradation and in turn reduces biodiversity. Soil is a habitat representing a complex mixture of inorganic and organic fractions, with water and living organisms. An array of the living organisms in three taxonomic domains is common in the soil (Woese et al, 1990). These are grouped into three broad diverse assemblage of the belowground biodiversity namely Bacteria, Arcaea and Eucaryota. The soil fauna, a part of Eucaryota is grouped into macrofauna, mesofauna and microfauna (Giller et al., 1997). These soil biota contribute positively to ecosystem processes (Swift and Bignell, 2000, Wall, 2004) which in turn support provision of ecosystems services that contribute to the maintenance and productivity of ecosystems by influencing soil quality and health (Brussaard et al., 1997; Kibblewhite et al., 2008). The soil quality and health influence fauna abundance and diversity. The belowground biodiversity has notable relevance to the health of crops, trees and plants desirable to man. Microorganisms like Trichoderma also play key roles in suppressing soil-borne plant diseases and promoting plant growth (Garbeva et al., 2004). Soil fauna play an important role of transforming the quality of soil by regulating the structure and functioning of microbial communities, shredding and digesting organic matter (Ponge et al., 2003). Among the mesofauna organisms, the CoUembola contribute immensely to the addition of soil nutrients through organic matter decomposition (Ponge et al., 2003).
Agricultural intensification involves high input application to replenish soil fertility, especially the use of inorganic fertilizers (Shriar, 2000; TSBF, 2003). Continued use of inorganic fertilizers has not only altered the pH soil, soil structure and texture but also disrupted the niches for micro-and mesofauna, which are essential for nutrient recycling (Ponge et al., 2003; Moreira et al., 2006). Presently, increased emphasis is on application of Integrated Pest Management (IPM). Farming practices such as IPM may affect abundance and diversity of the CoUembola as they are very sensitive to alteration in crop management practices (Rebek et al., 2002). Studies conducted on the effect of land use intensification, soil chemistry and soil organic matter on the abundance and diversity of CoUembola in France, Portugal and Brazil, have shown that, they have a significant effect on the population of CoUembola communities (Ponge et al., 2003; Jose' et al., 2004; 2005; Syrek et al., 2006). The CoUembola are sensitive to a wide range of micro-climatic changes and disturbances, inclusive of human activities hence are important bioindicators of the human induced changes in the soil systems (Lauga-Reyrel and Deconchat, 1999). There is limited information in Kenya on the influence of land use practices on belowground biodiversity (BGDB) especially the CoUembola communities which play a key role in organic matter decomposition. The purpose of the current study was to evaluate the effect of application of organic and inorganic fertilizer and Trichoderma in the soil on the abundance and diversity of the CoUembola communities.
MATERIALS AND METHODS
The study was conducted in two districts of Kenya, in Embu, Eastern Province and the Taita-Taveta in Coast Province, during the wet cropping and dry seasons of 2007 to 2009. The site in Embu was located at the Agricultural Training College (ATC) farm in Embu, at an altitude of 1480 m above sea level (Kiome and Muya, 1999). The soils are deep, well weathered with friable texture, with moderate to high fertility (Gachimbi, 2002). They are mainly Humic Nitisols (Jaetzold and Schmidt, 1983). The site in Taita-Taveta was located at the Taita Agricultural Training College (ATC) farm within Wundanyi division, at altitude 580 m above sea level. The soils are deep, well drained, dark brown varying from sandy clay loam to clay. In both sites the plots were established in an area which had been left fallow for two years. A block with seven plots, each measuring 3 m by 3 m with one meter footpath around the plots were established. All the plots were cultivated with a fork and properly leveled with a rake. Soil treatments/soil amendments were randomly allocated per plot except one plot which acted as control where no treatment was applied. This kind of set up was replicated five times hence five blocks each with seven plots. The soil treatment involved application of the following soil amendments; 1-Mavuno (Ma) P 50 kg per hectare, 2-Manure (Mn) 10 tons per hectare, 3-Trichoderna (Tr) seeds were coated with Trichoderma at rate of 2 grams of Trichoderma per one kilogram of seeds and gum Arabic used as a sticker, and 4-FP (Farmers practice where Triple Super Phosphate (T.S.P.) P 50 kg per hectare and Calcium Ammonium Nitrate (C.A.N.) N 100 kg per hectare was used), 5- Triple Super Phosphate (T.S.P.), 6-Calcium Ammonium Nitrate (C.A.N.) fertilizers was applied and 7-Control (Co)(plots where soil fertility management interventions where not applied). In the plots were Trichoderma was used, the seeds were inoculated through seed coating with Trichoderma at rate of 2 grams of Trichoderma per one kilogram of seeds and gum Arabic used as a sticker before planting. After broadcasting the inputs, they were mixed with the soil with a rake. All the plots including the control were then sown with maize (511 hybrid) at a spacing of 90cm x 30 cm, two seeds per hole and beans (Rose coco) two seeds per hole at spacing of 30 cm in alternate rows. The experiment was repeated for four consecutive seasons. In each plot, nine sub-samples of soil were collected to make composite of three samples. CoUembola were sampled using a soil core of 5 cm wide and at depth of 5 cm. CoUembola were extracted using dynamic behavioural modified Berlese funnel (Moriera et al., 2008) and were identified to the genus level (Hopkin, 2007).
Data collected was analyzed using analysis of variance (ANOVA). Prior to analysis, data were normalized using log transformation. Biodiversity descriptions estimated; genera abundance, richness StatSoft, 2003, Shannon diversity index (Kindt and Coe, 2005) and Renyi index. The mean values were compared using the Student Newmen Keulis Test (SNK) test (Zar, 1999) when ANOVAs were significant.
There were significant differences among soil fertility management treatments p≤0.0001 in terms of mean density of CoUembola in Embu and Taita soils (Table 1 and 2). In Embu, there was significant difference in mean density between control and all the other treatments. Application of organic inputs (cow manure and Trichoderma) increased abundance of the soil CoUembola while inorganic fertilisers impacted negatively p≤0.0001. In Embu the highest mean density of CoUembola was found in the control plots where no soil amendments was done, followed by treatments with manure and other organic treatments and the lowest abundance in treatments with inorganic amendments. In Taita, there was significant difference in mean density between organic amendments and inorganic amendments with low density recorded in plots with inorganic amendments. But densities were generally twice as high in Taita as in Embu. CoUembola sampled showed higher diversity in soils amended with organic manure to inorganic fertilisers.
There was higher abundance of CoUembola in year one than in second year. In both years during the four seasons both in Embu and in Taita, the highest mean density was recorded in the wet season and the lowest recorded in dry season. The same trend was evident with the mean richness, where diversity reduced with the increase in dry spell (Table 3 and 4).
A total of 969 individuals of soil dwelling Collembolan representing four families and nine genera were sampled from all the plots under different soil fertility management regimes in Embu. The genus Isotomiella was the most frequently sampled with cumulative frequency of 26.8%. Other genera were: Cryptopygus, Folsomina, Parisotoma, Lepidocyrtus, Ceratophysella, Folsomides, Tullbergia and Hypogastrura (Table 5). Most of the soil dwelling Collembola were sampled in control plots. Among the soil amendments, plots with cow manure and Trichoderma had the highest densities while lower densities were found in soils were only inorganic fertilisers were applied (Table 6). High and diverse soil Collembolan population were sampled in rainy season but, the trend is reversed in subsequent seasons. Organic amendments favoured species richness Shannon 1.861 (Table 7).
In Taita a total of 2688 soil dwelling Collembola represented in seven families and thirteen genera were sampled from all the plots under different integrated soil fertility management regimes. The genus Parisotoma was the most frequently sampled with cumulative frequency of 24.0%. Other genera were: Folsomia, Tullbergia, Oncopodura, Folsomides, Lepidocyrtus, Cryptopygus, Ceratophysella, Entomobrya, Isotoma, Thalassaphorura and Sminthurus (Table 8). High numbers of soil dwelling Collembola were sampled in control plots followed by plots with cow manure. A decrease in soil Collembola population was observed in soils were inorganic fertilisers like T.S.P. and C.A.N. were applied (Table 9). High soil Collembola population densities were sampled in season 1 and 2 but, numbers reduced progressively with higher diversity being realised in season 3 and 4. Cow manure and Trichoderma favoured species richness, Shannon 2.093 (Table 10).
The diversity profiles both in Embu and Taita of soil dwelling Collembola in the four seasons showed that wet season exhibited a higher diversity of Collembola than in the dry season. Plots with organic amendments and those which had no applications of any soil amendment supported a more diverse soil Collembola community than those where the inorganic fertilisers were used. The evenness profiles showed that wet season was most even with dry season being the least even. The treatment evenness profiles show that the plots where soil had been treated with cow manure and Trichoderma were more even while, the plots treated with inorganic fertilisers were less even.
Application of cow manure and Trichoderma in the soil during the growth period of the crop supported high abundance and diversity of Collembola as evidenced by the high numbers sampled in plots treated with the same. Several Collembola genera were sampled during the study. The genera include Isotomiella, Cryptopygus, Folsomina, Parisotoma, Lepidocyrtus, Folsomina, Oncopodura, Entomobrya, Isotoma, Thalassaphorura and Sminthurus. The varied genera occurrence may have been influenced by organic amendments which provided organic matter. The organic matter improves soil conditions, soil pH, and structure, water holding capacity and directly provide food resource for the eudaphic Collembola and indirectly crop growth like root residues. The findings agree with studies by (Lagerlof and Andrén, 1991, Mader et al., 1997 and Wardle et al., 1999a) who found that arthropod taxa are generally high at high organic matter input or in organic farming systems. Wachira, (2009) while evaluating the effect of organic amendments on nematode-destroying fungi and plant parasitic nematodes found that the use of chicken manure stimulated build-up of the nematode destroying fungi. We recorded few soil Collembola in plots that were treated with inorganic fertilisers (Mavuno, T.S.P. and C.A.N) over the four seasons. Probably, this may have been due to reduction in organic food resource and changes in soil conditions like soil pH, water holding capacity, bulk density and soil temperature. Similarly, inorganic fertilisers cause increased crop growth hence more water usage by the plant making the soil to have low moisture content essential for the Collembola. Filser et al., (1999) found that soil management practices contributed to the variation of microbial biomass. From this study, cow manure, application of Trichoderma on seeds before planting and the combination of cow manure and Trichoderma as well as lack of application of amendments over the time favoured Collembola population build up and diversity. Application of Trichoderma may have increased fungal flora and positively provided substrate for Collembola. Wachira, (2009) and Okoth, et al., (2009) have reported enhanced population build up of fungi like arthrobotrys species in organic amendment plots. High organic matter, shade, high soil carbon and nitrogen have a significant influence in supporting high population of soil Collembola and Mites (Muturi et al., 2009 and Maribie, 2009). The presence of organic manure resulted in an increase in the abundance and diversity of total collembolan. The genera Parisotoma and Isotomiella in the family Isotomidae were predominant which indicated that they benefited from the organic litter coming from manure which may have increased microbial biomass in the rhizosphere of roots. Rosilda et al., (2002) found that populations of soil Acari and Collembola increased with increase in organic matter content of the soil. The low numbers in presence of inorganic fertilisers implied that they negatively impacted on populations of Collembola. In this study high numbers of soil Collembola were sampled in the wet seasons in Embu and Taita. It implies that, soil Collembola population were dependant on soil moisture and to some extent the soil temperatures. The weather variation witnessed during the study characterised by the high temperatures may have led to either vertical migration of soil Collembola to the lower soil levels, aestivation, eggs remaining dormant or lower reproductive rate hence, the low counts recorded in the last dry season. Members of the family Isotomidae were most predominant in almost all plots may be due to their high reproductive rate and adaptive ability. The varied species abundance and diversity in the different seasons and in varied integrated soil fertility management practices is consistent with the findings by lauga-Reyrel and Deconchat, (1999) and Rosilda et ah, (2002), who reported that the group respond to changes in land use and soil conditions.
In conclusion the study has demonstrated the potential of organic soil amendments in enhancing edaphic soil Collembola as well as diversity due to the increased substrate niche for soil Collembola. However, dry conditions negatively affect the trend. Therefore, use of organic manure in agricultural fields would not only boost agricultural food production, but, also sustain soil Collembola which are important in nutrient cycling.
We would like to thank GEF for providing the financial support for this work and UNEP for providing the implementation support through the global project Conservation and Sustainable Management of Below-Ground Biodiversity (BGBD project) that is being implemented in seven tropical countries namely: Brazil, Cote d'lvoire, India, Indonesia, Kenya, Mexico and Uganda. TSBF-CIAT is acknowledged for planning and coordinating project activities. Special thanks to Dr. Sheila Okoth, the Below Ground Project Coordinator in Kenya for her enviable support throughout the study period. We sincerely thank Dr. Arne Fjellberg and Prof. Louis Deharveng for assisting in the systematic of Collembola. Special thanks are also extended to Dr. Wachira, Mr. Crispus Maribie, Miss Agnes Mkamaghanga, Mr. Munyi and Mr Josek Mugendi for their support both in the field and in the laboratory.
Brussaard, L.; Behan-Pellertier, V.; Bignell, D.; Brown, V.; Didden, W.; Folgarait, P.; Fragoso, C; Freckman, D.; Gupta, V.; Hattori, T.; Hawksworth, D.; Klopatek, C; Lavelle, P.; Malloch, D.; Rusek, I; Soderstrom, B.; Tiedje, J. and Virginia, R. 1997. Biodiversity and ecosystem functioning in soil, Ambio, 26:563-570 [ Links ]
Filser, J.; Fromm, H.; Lang, A.; Mebes, K. H.; Munch, J. C; Nagel, R.; Winter, K.; Beese, F. 1999. Reactions of soil organisms to site-specific management: the first long-term study at the landscape scale. In: Windhorst, W., Enckell, P. H. (Eds), Proceedings of the Conference "Sustainable Landuse Management-The Challenge of Ecosystem protection", 28.9.-1.10.99, Salzau Federal Cultural Center, Organizers: University of Kiel/European Ecological Federation. Verein Zur Förderung der Ökosystem forsclung an Kiele. V., ISSN 0940-7782. Ecosystems Supplementary Biodiversity, 28, 139-147 [ Links ]
Fjelberg, A. 1997. Nordic Collembola: Identification keys to genera. Checklist of species. Swedish University of Agricultural Sciences (mimeograph), 30p [ Links ]
Gachimbi, L. N. 2002. Technical Report of Soil Survey and Sampling results: Embu Mbeere Districts, Kenya. The land use change, Impacts and Dynamics project working paper Number: 9 [ Links ]
Garbeva P.; van Veen and van Elsas, J. D. 2004. Microbial diversity in soil: selection of microbial populations by plant and soil type and implications for disease suppressiveness. Annual Review Phytopathology 42: 243-270 [ Links ]
Giller, K. E.; Beare, G. G.; Lavelle, P.; Izaac, A. M. M. and Swift, M. J. 1997. Agricultural intensification, Soil biodiversity and agro ecosystems function. In Swift, M. J. (ed.), Soil biodiversity agricultural intensification and ecosystem function. Applied Soil Ecology 6: 3-16 [ Links ]
Hopkin, S. P. 2007. A Key to the Collembola (Springtails) of Britain and Ireland. 1st edition, FSC Publications Shropshire, UK [ Links ]
Jeatzold, R. and Schmidt, H. 1983. Farm Management Handbook of Kenya. Vol. II/L. East Kenya. Ministry of Agriculture. Nairobi, Kenya [ Links ]
José, P. S., Maria, M. G., Cristina, P., Antonio, K., Filipa C, Marco, L., Catarina, C, Taigo, L., Pedro, L. and Susana, D. 2004. Effect of land use on Collembola diversity patterns in a Mediterranean landscape. Pedobiologia 48: 609-622 [ Links ]
José, P. S., Thomas, B., Maria, M. M., Thomas, L., Jean-Francios, P., Carlos, S., Georgy, T., Adam, J. V, Aoife, B., Florence, D. Eva, I., Anto'nio, K., Silvia, S. and Allan, D. W. 2005. Changes in Collembola richness and diversity along a gradient of land-use intensity: A pan European study. Pedobiologia 50: 147-156 [ Links ]
Kibblewhite, M. G.; Ritz, K. and Swift, M. J. 2008. Soil health in agricultural systems. Philosophical Transactions of the Royal Society Series B 363: 685-701 [ Links ]
Kindt, R and Coe, R. 2005. Tree diversity analysis. A manual and sotware for common statistical methods for ecological and biodiversity studies. Nairobi: World Agro-forestry Center (ICRAF). Pg 196 [ Links ]
Kiome, R. L. and Muya, E. M. 1999. Characterisation of soil Embu and Kiambu PLEC sites. PBL. Kenya Soil Survey. Site Evaluation report no. 61 [ Links ]
Lagörlof, J. and Andrén, O. 1991. Abundance and activity of Collembola, Protura and Diplura (Insecta, Apterygota) in four cropping systems. Pedobiologia, 35: 337-50. [ Links ]
Luanga-Reyrel, F. and Deconchat, M. 1999. Diversity within the Collembolan community in fragmented coppice forests in South-Western France. European journal of Soil Biology 35: 177-187 [ Links ]
Mäder, P.; Pfiffner, L.; Fließbach, A.; von Lützow, M; Munch, J. C. 1997. Soil ecology-the impact of organic and conventional agriculture on soil biota and its significance for soil fertility. In: Østergaard, T. V. (Ed), Fundamentals of Organic Agriculture. Proceedings of the 11th IFQAM International Scientific Conference, vol. 1, pp. 24-46, Copenhagen [ Links ]
Maribie, C. W. 2009. Survey of soil mites (Acari) abundance and diversity in different land use types in Embu and Taita districts, Kenya Msc Thesis University of Nairobi [ Links ]
Mokwunye, A. U.; De Jager and Smaling, E. M. A. (ed). 1996. Restoring and maintaining the productivity of West African soils: Key to sustainable development. Misc. Fert. Stud. 14. Int. Fert. Dev. Ctr. - Africa. Lome, Togo [ Links ]
Moreira, F. M. S.; Huising, E. J.; Bignell, D. E. 2008. A Handbook of Tropical Soil Biology: Sampling and Characterization of Below Ground Biodiversity. Earthscan, UK 218 pp. [ Links ]
Moriera, F. M. S.; Siquera, J. O. and Brassard, L. 2006. Soil organisms in Tropical Ecosystems: a key role for Brazil in the Global Quest for the conservation and sustainable use of Biodiversity. Soil Biodiversity in Amazonian and other Brazilian Ecosystems, CAB International, Wallingfork, UK, pp 1-12 [ Links ]
Muturi, J. J.; Mbugi, J. P.; Mueke, J. M.; Lagerlóf, J.; Mungatu, J. K.; Nyamasyo, D. and Gikungu, M. 2009. Collembola density and diversity along a gradient of land-use types in Embu district, Eastern Kenya. Tropical and Subtropical Agroecosystems, 11, 361-369 [ Links ]
Okoth, S. A.; Okoth, P.; Wachira, P. M. amd Roimen, H. 2009. Spatial distribution of Trichoderma spp. In Embu and Taita regions, Kenya. Tropical and Subtropical Agroecosystems. 11:291-302 [ Links ]
Ponge, J. F., Gillet, S., Dubs, F., Fedoroff, E., Haese, L., Sousa, P. J. and Lavelle, P. 2003. Collembola communities as bioindicators of land use intensification. Soil biology and biochemistry 35: 813-826 [ Links ]
Rebek, E. J.; Hogg, D. B. and Young D. K. 2002. Effect of four cropping systems on the abundance and diversity of epedaphic springtails (Hexapoda: Parainsecta : Collembola) in Southern Wisconsin. Environmental Entomology 31: 37-46 [ Links ]
Rosilda, M.M., Silvana de Paula, Q. S., Sandra, V., and Valdirene, R. S. 2002. Study of Acari and Collembola Populations in Four Cultivation systems in Dourados-MS. Brazilian Archives Biology Technology. 45 : 257-264. [ Links ]
Sanchez, P. A.; Sheperd, K.D.; Soule, F.; Place, M.; Buresh, R. J. and Izac, A. M. N. 1997. Soil Fertility repleshment in Africa. An investment in Natural Resource Capital. In: R. J. Buresh et al (Ed) Replenishing soil fertility in Africa. SSA Spec. Publ. 51. SSSA, Madison, W. I. [ Links ]
Shriar, A. J. 2000. Agricultural intensity and its measurement in frontier regions. Agroforestry systems 49: 301-318 [ Links ]
StaftSoft, Inc, 2001. STATISTICA (Data Analysis Software System), Version 6. Tulsa, OK, USA [ Links ]
Swift, M. J. and Bignell, D. (eds), 2000. Standard methods for assessment of soil biodiversity and land use practice. Alternatives to Slash and Burn Project. ICRAF, Nairobi. 41pp [ Links ]
Swift, M. J. and Shepherd K. D. (eds), 2007. Saving Africa's Soils: Science and Technology for Improved Soil Management in Africa: World Agroforestry Centre. [ Links ]
Syrek, D., Wiener, W. M.., Wolty, M. Olszowska, G. and Kwapis, Z. 2006. Species abundance distribution of Collembolan communities in forest soils polluted with heavy metals. Agriculture, ecosystems and environment. Applied Soil Ecology. 31: 239-250 [ Links ]
TSBF, 2003. Conservation and Sustainable management of below ground biodiversity. Proceedings of the global workshop held in February 24-28, 2003 in Sumberjaya, Lampurg, Indonesia. Global workshop report No. 11 [ Links ]
Wachira, P. M. 2009. Effect of land use and soil fertility management practices on nematodes destroying fungi in Taita Taveta, Kenya PhD Thesis University of Nairobi [ Links ]
Wall, D. H. (ed) 2004. Sustaining Biodiversity and Ecosystem Services in Soils and Sediments, Island Press, Wahington, D. C. [ Links ]
Wardle, D. A.; Nicholson, K. S.; Bonner, K. I.; Yeates, G. W. 1999a. Effects of agricultural intensification on soil-associated arthropod population dynamics, community structure, diversity and temporal variability over a seven-year period. Soil Biology biochemistry. 31, 1691-1706 [ Links ]
Woese, C. R.; Kandler, O. and Wheelis, M. L. 1990. 'Towards a natural system of organisms: proposal for the domains Archaea Bacteria, and Eucarya', Proceedings of the national Academy of Sciences USA, vol, pp 4576-4579 87 [ Links ]
Zar, J. (1999). Biostatistical Analysis. (4th ed.) Upper Saddle River, NJ, Prentice Hall [ Links ]