Influence of species of VA mycorrhizal fungi on cassava yield Response to phosphorus fertilization

A three different sites with acid soils in Colombia field trials with cassava were monitored for frequency of VA mycorrhiza. Increasing levels of phosphorus (P) from 0 to 200 kg P/ha had been applied. The fields differed in the composition of species of VA mycorrhizal fungi. At all sites infections of the roots by the total mycorrhizal population decreased with increasing P fertilization, but at two sites the relative frequency and activity of one species,Glomus manihotis, increased with increasing P applications. This species was only present at two sites, and only in these sites a cassava yield response to up to 200 kg P was found. The differential activity of fungal species was confirmed in greenhouse trials, whereEntrophospora colombiana was found to be most effective at 50 kg P andG. manihotis, at 200 kg P