A field trial on alley-cropping was conducted at the University of Ibadan research farm in the 1990/91 cropping season to assess the contributions of arbuscular mycorrhizal (AM) fungi and hedgerow woody legumes to the yield and nutrient uptake of cassava (Manihot esculenta Crantz) as an intercrop in an infertile soil. The trial also investigated the influence of AM fungi on the interplanting of a non-nodulating woody legume Senna siamea (syn. Cassia siamea) with a nodulating woody legume (Leucaena leucocephala).

AM contributions to cassava were greater than the hedgerow contributions, which demonstrated that AM associations are an essential component in the nutrition of cassava. In contrast to cassava, AM inoculation only influenced the leaf dry weight and uptake of nutrients of non-interplanted woody legumes but not the above-ground biomass and P uptake of interplanted woody legumes. However, non-inoculated interplanted Leucaena benefited more from indigenous AM fungi than the competing Senna. The negative contributions to the nutrient uptake (K, Ca and Mg) of cassava by hedgerows and the lack of response to AM inoculation in interplanted hedgerow woody legumes could be attributed to root competition among the different plant species growing in close proximity to each other. The present results show that cassava benefits more from AM association than Leucaena which in turn benefits more than Senna in an alley-cropping system.