Seedlings of Acacia auriculiformis A. Cunn. ex. Benth., Albizia lebbeck (L.) Benth., Gliricidia sepium (Jac.) Walp and Leucaena leucocephala (Lam.) de Wit. were inoculated with an ectomycorrhizal (Boletus suillus (L. ex. Ft.) or indigenous vesicular-arbuscular mycorrhizal (VAM) fungi in a low P soil.The plants were subjected to unstressed (well-watered) and drought-stressed (water-stressed) conditions. In Gliricidia and Leucaena, both mycorrhizal inoculations stimulated greater plant growth, P and N uptake compared to their non-mycorrhizal (NM) plants under both watering regimes. However, in Acacia and AIbizia, these parameters were only stimulated by either ectomycorrhiza (Acacia) or VA mycorrhiza (Albizia). Growth reduction occurred as a result of inoculation with the other type of mycorrhiza. This was attributed to competition for carbon between Acacia and VA mycorrhizas and parasitic association between Albizia and ectomycorrhiza.Drought-stressed mycorrhizal and NM Leucaena, and drought-stressed mycorrhizal Acacia tolerated lower xylem pressure potentials and larger water losses than the drought-stressed mycorrhizal and NM Albizia and Gliricidia. These latter plants avoided drought by maintaining higher xylem pressure potentials and leaf relative water content (RWC). All the four leguminous plants were mycorrhizal dependent. The higher the mycorrhizal dependency (MD), the lower the drought tolerance expressed in terms of drought response index (DRI). The DRI may be a useful determinant of MD, as they are inversely related.

Previous work suggests that some sweet potato (Ipomoea batatas, L.) cultivars can produce high storage root yields on soils without fertilizer N addition. This study was conducted to compare storage root yields, total biomass, N uptake and fibrous root weights of sweet potato cultivars grown on low N level soils with and without N addition. In 1987 and 1988, improved sweet potato cultivars developed at International Institute of Tropical Agriculture (liT A), Ibadan, Nigeria were grown with and without 50 kg N ha-1 in Oxic Paleustalfs with low N and C concentrations. Yields of 21 to 38 Mg ha-1 were produced for four of the five improved cultivars grown in soil without N addition. Total biomass, foliage, fibrous root and storage root weights and N concentration in leaves were not influenced by fertilizer N addition. Up to 158 and 89 kg N ha-1 uptake in total biomass occurred with the + N and -N treatments, respectively. Indigenous soil N levels and fibrous root weights for -N vs. + N treatments could not account for the total N uptake and biomass produced on soils without N addition.

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A greenhouse investigation was conducted to determine the effect of arbuscular mycorrhiza and drought on the growth of two tropical hedgerow legume trees (Gliricidia sepium and Leucaena leucocephala) under simulated eroded soil conditions. It was a factorial design with two levels of watering regime (adequate watering and drought), inoculation with Glomus deserticola

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