Allelopathic effects of Calliandra calothyrsus Meisn, Senna siamea L. and Gliricidia sepium (Jacq.) Walp Leaves on Maize (Zea mays L.) and Bean (Phaseolus vulgaris L.) Root and Shoot Growth

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 = Calliandra calothyrsus. 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. Physiological processes affected by allelochemicals are wide and varied [9, 16]: cell division; change in hormonal synthesis, equilibrium and regulation; biosynthis of cellular constituents; enzymatic activity; plant-water relationships; photosynthesis and respiration; plasma membrane permeability of the roots; pollen tube germination; protein synthesis; root elongation; rate of ion absorpltion by plants; pigment and changes in DNA and RNA structure; mitotis; reduction of flower and fruit formation, inhibition or stimulation of stomatal opening and conductance; changes in lipids and organic acid metabolism. effect on bean and maize early growth parameters followed the order: Gliricidia sepium > Senna siamea = Calliandra calothyrsus . This study outlines the potential detrimental effect of agroforestry species foliar biomass on associated plant growth when directly applied to soil. As an alternative, we recommand 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.