Beneficial effects of Leucaena Rhizobium association on coffee in Burundi. - (:unkn) unknown
Laboratory and field trials were carried out in the 3 main coffee growing regions of Burundi to find an appropriate legume to plant in coffee and to investigate the optimization of biological nitrogen fixation (BNF), the transfer of N fixed by the legume to the coffee plants and the cultural methods best suited to the constraints of the association. Of 3 legume genera considered (Desmodium, Leucaena and Flemingia), 2 Leucaena species were recommended L. diversifolia over 1500 m and L. leucocephala under 1500 m. As most coffee plantations are above 1500 m asl and this species was seen to fix N very well, L. diversifolia was used for further studies. The Rhizobium strain associated with this species (IRAT K156) was isolated and was found to exist in soils in all 3 regions of the study. Microbiological methods were used to determine the best conditions for the growth of this native strain and an imported Rhizobium strain and to find the soil amendments required to improve plant growth and BNF in the field. Studies were then carried out to determine variations in N fixation activity over time, taking into account how the legumecoffee tree combination was managed (e.g. cutting). Isotopic measurement techniques were used to evaluate N flow in the soil and in the plant and to assess the benefit to coffee trees of BNF by legumes grown as hedges in the plantation. It was concluded that Leucaena is suitable for growing with coffee as it provides organic matter (prunings) and nitrogen and protects the soil from erosion and evaporation.
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Laboratory and field trials were carried out in the 3 main coffee growing regions of Burundi to find an appropriate legume to plant in coffee and to investigate the optimization of biological nitrogen fixation (BNF), the transfer of N fixed by the legume to the coffee plants and the cultural methods best suited to the constraints of the association. Of 3 legume genera considered (Desmodium, Leucaena and Flemingia), 2 Leucaena species were recommended L. diversifolia over 1500 m and L. leucocephala under 1500 m. As most coffee plantations are above 1500 m asl and this species was seen to fix N very well, L. diversifolia was used for further studies. The Rhizobium strain associated with this species (IRAT K156) was isolated and was found to exist in soils in all 3 regions of the study. Microbiological methods were used to determine the best conditions for the growth of this native strain and an imported Rhizobium strain and to find the soil amendments required to improve plant growth and BNF in the field. Studies were then carried out to determine variations in N fixation activity over time, taking into account how the legumecoffee tree combination was managed (e.g. cutting). Isotopic measurement techniques were used to evaluate N flow in the soil and in the plant and to assess the benefit to coffee trees of BNF by legumes grown as hedges in the plantation. It was concluded that Leucaena is suitable for growing with coffee as it provides organic matter (prunings) and nitrogen and protects the soil from erosion and evaporation.
Keywords: agroforestry systems; agroforestry; agrosilvicultural systems; Coffea.; cropping systems; erosion control; Erosión.; intercropping; legumes; nitrogen fixation; nitrogen fixing bacteria; nitrogen fixing trees; stimulant plants; tropical crops; Agroforestry systems; Agroforestry; Cropping systems; Intercropping; Legumes; Nitrogen; Tropical crops