Root system characteristics with agroforestry relevance of nine leguminous tree species and a spontaneous fallow in a semi-deciduous rainforest area of West Africa

Abstract

The use of tree root characteristics as criteria in the selection of agroforestry tree species is hampered both by uncertainties in the definition of an ideal tree root system and by the scarcity of information which relates tree root properties to the effects of the trees on the soil and associated plant species. In the present study, carbon and nitrogen accumulation in roots (under 5 mm in diameter) of nine leguminous tree species and a spontaneous Chromolaena odorata fallow were investigated on a Ferralic Cambisol in the semi-deciduous rainforest zone of West Africa. Root-C in 0–60 cm soil depth ranged from 1049 to 3304 kg ha−1, and root-N ranged from 41.5 to 133 kg ha−1. The sponaneous vegetation had a particularly low subsoil root mass compared with the trees. Differences in subsoil root mass could be related to the physical amelioration of a compacted soil horizon. Trees with high root mass tended to have little understorey vegetation, indicating that the latter was controlled by below-ground competition of the trees, in addition to shading. The root characteristics of the tree species are discussed with respect to their potential value for different agroforestry technologies.