Planted Tree Fallows and Their Influence on Soil Fertility and Maize Production in East Africa Nitrogen Fixation and Soil Nitrogen Dynamics

Ståhl, L. 2005. Planted tree fallows and their influences on soil fertility and maize production in East Africa. Nitrogen fixation and soil nitrogen dynamics. Doctor´s dissertation. ISSN1652-6880, ISBN 91-576-6908-2 Soil fertility depletion is a main constraint to food production in sub-Saharan Africa. This thesis concerns the potential of N2-fixing trees to increase nitrogen inputs to agroforestry systems and accordingly to improve crop production. The suitability of five tropical tree species (including two N2-fixing species, Leucaena leucocephala and Prosopis chilensis) for tree fallows in Tanzania were evaluated by comparing their leaf chemistry, their effects on soil properties and on maize growth. After five years fallow, the per cent total soil N was higher under Prosopis compared to under other tree species. Maize biomass production was higher on soils from Leucaena or Prosopis compared to grass fallow. Prosopis contributed 11 % to the total soil C over a period of 8 years. Field experiments in Kenya were performed to test a low-level 15N-tracer technique t