B.Sc., Moi University, Kenya, 1990
Ph.D., Wye College, University of London, 2000

Nutrient management in natural and managed terrestrial ecosystems; biogeochemical processes in nutrient cycling and productivity in seasonal wetland ecosystems; microbial activity and nutrient pools in relation to ecosystem functioning; temporal soil nitrogen mineralization, denitrification and nitrous oxide flux in grazed pastures; Organic matter storage and carbon sequestration; Soil nutrient sourcing and contribution of legume nitrogen fixation relative to the overall nitrogen budget in tropical tree-crop based agroforestry systems.

Current research and responsibilities:

1. Biogeochemical processes and nutrient cycling (mainly carbon, nitrogen and phosphorus) in seasonal wetlands as influenced by land use and cattle stocking densities in subtropical rangelands (see photos, this page).
2. Water quality and algal productivity as affected by land-use in seasonal wetlands surrounded by improved and semi-native pasture systems.
3. Technical supervision of research assistants working for the project on all aspects of research.
4. Assist in the overall administration of the project.

1. Gathumbi, S.M., Cadisch, and K.E. Giller. 2004. Improved fallows: effects of species interaction on growth and productivity in monoculture and mixed stands. Forest Ecology and Management 187:267-280.

2. Gathumbi, S.M. 2004. Root recovery of five tropical tree and shrubby species by sieves of different mesh sizes. Agroforestry Systems 60:233-237.

3. Mafongoya, P.L., K.E. Giller, D. Odee, A. Bala, J.K. Ndufa, S.M. Gathumbi, M. Wong, and S.M. Sitompul. 2004. Benefiting from N₂-fixation and managing rhizobia: Below-ground transfer and contribution to subsequent crops. In C. Ong et al. (ed.) Below-ground interactions in tropical agroforestry concept and model with multiple plant components. CAB International, Wallingford, U.K. In press-April 2004

 4. Gathumbi, S.M., G. Cadisch, and K.E. Giller. 2003. Subsoil nitrogen capture in mixed legume stands as assessed by deep ¹⁵N placement. Soil Science Society of America Journal 67:573-582.

5. Gathumbi, S.M., G. Cadisch, and K.E. Giller. 2002. 15N natural abundance as a tool for assessing N2-fixation of herbaceous, shrub and tree legumes in improved fallows. Soil Biology and Biochemistry 34:1059-1071.

 6. Gathumbi, S.M., J.K. Ndufa, K.E. Giller, and G. Cadisch. 2002. Do species mixtures increase above- and below-ground resource capture in woody and herbaceous tropical legumes? Agronomy Journal 94:518-526. (highlights published in CSA News and posted in Agronomy website).

7. Cadisch, G., S.M. Gathumbi, J.K. Ndufa, and K.E. Giller. 2002. Resource acquisition of mixed species fallows-competition or complementarity? p. 143-154. In B. Vanlauwe, et al. (ed.) Integrated nutrient management in sub-Saharan Africa. CAB International, Wallingford, U.K.

 8. Niang, A.I., B. Amadalo, Y. de Wolf, and S.M. Gathumbi. 2002. Species screening for short term planted fallows in the highlands of western Kenya. Agroforestry Systems 56:145-154.

 9. Odee, D. W., M. Esitubi, J. Machua, J.M. Njoroge, J. Ochieng, K.A. Mwendwa, S.M. Gathumbi, W. Omondi, and A.I. Niang. 1998. On-farm evaluation of indigenous rhizobia associated with leguminous trees and shrubs for improved fallow systems in Africa: Linking process to progress. p. 195-201. In F. D. Dakora (ed.) Proceedings of the 8th congress of the African association for biological nitrogen fixation. University of Cape Town, Cape Town, South Africa.

 10. Niang, A.I., S.M. Gathumbi, and B. Amadalo. 1996. The potential of short duration improved fallow for crop productivity enhancement in the highlands of western Kenya. East Africa Agricultural and Forestry Journal 62:103-114.

 11. Niang, A.I., B. Amadalo, S.M. Gathumbi, and C. Obonyo. 1996. Maize yield response to green manure application from selected shrubs and tree species in western Kenya: A preliminary assessment. East Africa Agricultural and Forestry Journal 62:199-207.

 12. Niang, A.I., S.M. Gathumbi, and B. Amadalo. 1996. The potential of short duration improved fallow for crop productivity enhancement in the highlands of Western Kenya. p. 218-230. In E.J. Carter et al. (ed.) People and Institutional Participation in Agroforestry for Sustainable Development. ICRAF, Nairobi, Kenya.

 13. Nyamai, D.O., S.M. Gathumbi, P. Juma, and J.C. Njuguna. 1996. Hedgerow intercropping for soil fertility improvement and management: A synthesis of various studies conducted in western Kenya. p. 231-258. In E.J. Carter, et al. (ed.) People and Institutional Participation in Agroforestry for Sustainable Development. ICRAF, Nairobi, Kenya.

 14. Niang, A.I., B. Amadalo, S.M. Gathumbi, and C. Obonyo. 1996. Maize yield response to green manure application from selected shrubs and tree species in western Kenya; A preliminary assessment. p. 350-258. In E.J. Carter et al. (ed.) People and Institutional Participation in Agroforestry for Sustainable Development. ICRAF, Nairobi, Kenya. 

1. Gathumbi, S.M., P.J. Bohlen, and D.A. Graetz. 2004. Nutrient enrichment of wetland plants and sediments in subtropical pastures. Soil Sci. Soc. Am. J. Submitted. 

1. Bohlen, P.J., S.M. Gathumbi, and D.A. Graetz. 2004. Soil N mineralization and denitrification in seasonal wetlands of sub-tropical rangeland ecosystems. Soil Sci. Soc. Am. J. In preparation. 

2. Gathumbi, S.M., P.J. Bohlen, D.A. Graetz, and A.D. Steinman. 2004. Implications of cattle grazing on vegetation dynamics and within-stand nutrient cycling in temporary wetland ecosystems. Ecological Applications. In preparation. 

3. Christoffersen, B.J., P.J. Bohlen, and S.M. Gathumbi. 2004. Impact of grazing activity and hydrologic fluctuations on denitrification in subtropical wetlands. In preparation. 

4. Gathumbi, S.M., and P.J. Bohlen. 2004. Nitrogen mineralization potential of plant residues in soils from grazed seasonal wetlands of subtropical rangelands. In preparation.