Mycorrhizal relations in trees for agroforestry and land rehabilitation

The mycorrhizal stimulation of trees by increasing the efficiency of nutrient uptake from soil is discussed with special reference to tree species used in agroforestry/sylvopastoral systems. The occurrence of the two major classes of mycorrhizas is indicated as are the soil, plant and fungus factors affecting the size of the response. The low intensity of rooting of many tree species and the prevalence of low fertility soils suggest large responses may be obtained frequently by inoculation with mycorrhizal fungi selected for high efficiency or by management to increase populations of indigenous fungi where these are highly effective but low in number. Effective mycorrhiza function may also ameliorate deleterious soil conditions other than nutrient deficiency and is important to maximize symbiotic nitrogen fixation. Inoculation of tree species in the nursery is logistically feasible and inoculated arbuscular mycorrhizal trees, when outplanted, may serve as inoculum sources for interrow crops. Future avenues of research are indicated.