THE MANAGEMENT OF POPULATIONS OF VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI IN ACID-INFERTILE SOILS OF A SAVANNA ECOSYSTEM .2. THE EFFECTS OF PRECROPS ON THE SPORE POPULATIONS OF NATIVE AND INTRODUCED VAM-FUNGI

A field trial conducted over two seasons in the savanna ecosystem in the eastern plains of Colombia was sequentially sampled to assess the effects of phosphate (P) source and plant host on the introduced and indigenous vesicular-arbuscular mycorrhizal fungi (VAMF) spore populations at two field sites. Spore densities were greatest under Sorghum sp. 5 months after sowing in both inoculated and non-inoculated sub-plots at both sites. The major sporulators in all Sorghum sub-plots 5 months after sowing were from the Glomus occultum/Acaulospora myriocarpa morphological grouping. Spore numbers of the introduced Glomus manihotis isolate were specifically increased in inoculated cassava (Manihot esculenta) sub-plots 5 months after sowing. Total spore numbers declined rapidly during the 4 month dry season but increased again under cowpea (Vigna unguiculata) at one site 15 months after trial establishment. At this stage spore numbers were greatest under cowpea growing on plots previously cropped with kudzu (Pueraria phaseoloides) and comprised predominantly spores of the Entrophospora colombiana/Acaulospora mellea/Acaulospora morrowae morphological group. The data are discussed in terms of their use in the management of VAMF populations for the benefit to plant growth in acid-infertile soils. © 1990 Kluwer Academic Publishers.