A large number of useful tropical plant species are dependent on mycorrhizal fungi. Without the fungal symbionts they show growth depression and lower tolerance to biotic and abiotic stresses. In plant production systems, common management practices normally result in symbiosis deficits. In tropical regions where the system of shifting cultivation is practiced, the fallow period was thought to have a positive regulating effect on the mycorrhizal situation. It's showed that between three and eight years of fallow there is an increase of the inoculum potential in the soils but the effectivity of the fungal populations remains very low in comparison to the populations from natural sites. The need to manage the mycorrhizal fungi in situ in the field is discussed
