Growth responses of mycorrhizal and non-mycorrhizal tropical forage species to different levels of soil phosphate

Three tropical forage legumes, Stylosanthes capitata, Pueraria phaseoloides and Centrosema macrocarpum, and one grass, Brachiaria dictyoneura, were grown in a sterile phosphate deficient soil amended with soluble or rock phosphate at rates ranging from 0 to 400 mg kg^-1 soil. The effects of inoculation with Glomus manihotis on mycorrhizal infection and plant growth were assessed. Early growth and nodulation of P. phaseoloides in soil with and without rock phosphate fertilizer were also determined. In the legumes, mycorrhizal infection was high at all P levels and sources, except for a significant decrease of infection in S. capitata at high levels of superphosphate. Plant growth was significantly increased by phosphate fertilizer and mycorrhizal inoculation. Mycorrhizal responses were more pronounced at low P levels with both P sources. In B. dictyoneura mycorrhizal infection was decreased with increasing additions of P. No effects of mycorrhizal inoculation (except with no added P) were observed. Growth and nodulation of P. phaseoloides were greatly stimulated by mycorrhizal inoculation.