Mycorrhizal inoculation effects on continuous hedgerow-biomass production and nutrient contribution to alley-cropped cassava in Ibadan, Nigeria

An alley cropping plot was established in 1990 on a degraded alfisol on sloping land at Ajibode village near the University of Ibadan, Nigeria. The influence of Glomus deserticolum on biomass production of three hedgerow trees i.e., Leucaena leucocephala, Gliricidia sepium and Senna siamea, and their nutrient contribution to cassava Manihol esculenta in four consecutive cropping seasons were investigated. Inoculation only promoted hedgerow leaf-biomass and nutrient (N, P, and K). contribution to cassava and consequently cassava tuber yield in the second year but did not affect them afterwards despite increased AM infection. Tuber yield declined with succeeding cropping seasons in all plots except uninoculated plots with Senna where it showed 142% and 11.5% increases respectively at 2 and 3-months pruning regime when compared with the first year’s yield. Biomass production increased marginally with age in all hedgerows with concomitant increase in leaf production depending on partitioning of assimilates between leaf and stem. Generally, hedgerow biomass diversion to leaf was higher at 2 than at 3-month pruning regime and was in the order Senna Gliricidia Leucaena. Hence, while Senna provides sustained adequate leaf mulch to cassava, pruning at quarterly interval during the first pruning year and at bimonthly intervals in subsequent years is also recommended.