Using the soils containing several arbuscular mycorrhizae, the degrees of infection on the plant roots were measured with the different level of phosphate added on pot cultures. Infection on the plant roots was independent of the phosphate level for the roots of sorghum, but formation of arbuscular mycorrhizae in the roots was inversely related to the growth of soybean roots. It was concluded that infection of arbuscular mycorrhizae would be related to the phosphate level in the soils. Plants, themselves, were considered to control the infection of arbuscular mycorrhizae under the environments of soils, especially amount of phosphate.