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With the promotion of so-called multipurpose agroforestry species in Burundi, Calliandra calothyrsus Meisn, Senna siamea L. and Gliricidia sepium (Jacq.)Walp have been the three widely disseminated leguminous shrubs to farmers for use as climbing bean stakes, fuelwood, fodder and green manure. However, of recent, field reports indicate that direct application of their foliar biomass as green manure show some negative effects on plant growth. For that matter, laboratory and greenhouse studies were set up to examine and compare the susceptibility of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) to allelopathic effects of Calliandra calothyrsus Meisn, Senna siamea and Gliricidia sepium (Jacq.) Walp. Data were collected on seed germination, radicle elongation, root and shoot growth, root, shoot and total dry biomass. The study revealed tangible depressive effects of leaves of all three tested leguminous species, particularly on radicle elongation, root and shoot growth of tested crop species. The inhibitory effects were more pronounced at higher application rates on bean than on maize growth, while roots were more sensitive than shoots. This is an indication that allelochemicals are not only species specific, but also organ specific as well as concentration dependent. Overall, the allelopathic effect followed the order: Gliricidia sepium > Senna siamea = Calliandracalothyrsus. The study outlined the potential detrimental effect of agroforestry species foliar biomass on associated plant growth when directly applied to the soil. As an alternative, we recommend to farmers the co-composting approach with low quality crop harvest residues (e.g. maize stover, wheat straw), in which the leguminous leaves play a stimulatory effect on the overall decomposition, allelochemicals dissipation and plant nutrient release. |
