THE EFFECT OF VESICULAR-ARBUSCULAR MYCORRHIZAL INOCULATION ON NUTRIENT-UPTAKE AND YIELD OF ALLEY-CROPPED CASSAVA IN A DEGRADED ALFISOL OF SOUTHWESTERN NIGERIA

Leaf and root (tuber) nutrient uptake patterns of cassava (Manihot esc ulenta Crantz) alley-cropped with gliricidia (Gliricidia sepium), leuc aena (Leucaena leucocephala), and senna [(Senna (syn. Cassia) siamea] as influenced by vesicular-arbuscular mycorrhizal (VAM) inoculation in a degraded Alfisol were investigated in 3 consecutive years. The cass ava plants were mulched with fresh prunings of each hedgerow tree spec ies at 2-month intervals in the second and third years of alley croppi ng. While VAM inoculation significantly influenced the root uptake of nutrients, the leaf uptake was not affected except for the uptake of P . In most cases, there was no difference in the nutrient concentration between inoculated and uninoculated plants, either in the leaf or in the root, indicating that the productivity of cassava was regulated by the amount of nutrients the roots could absorb. In spite of similar t otal soil N in all inoculated and uninoculated alley-cropped cassava p lots and similar exchangeable soil K contents in inoculated and uninoc ulated alley-cropped cassava plots with leucaena and senna, greater up take of N, P, and K and greater concentrations of K were observed in r oots of inoculated alley-cropped cassava with gliricidia and leucaena than with senna. These results indicated that greater mineralization a nd availability of nutrients to cassava roots from prunings of nodulat ing gliricidia and leucaena than from non-nodulating senna may be impo rtant, particularly with efficient VAM inoculation, in these alley-cro pping systems. Also, for similar nutrients in the inoculated and unino culated cassava soils alley-cropped with each hedgerow species, VAM in oculation significantly enhanced cassava root dry weights, indicating that an effective VAM fungus can be an agent of greater nutrient uptak e in a competitive environment.