Phosphate rock (PR) has been identified as a cheap supplementary source of phosphate for low pH oils. Arbuscular mycorrhizae (AM) improve plant uptake of P and other nutrients in acidic, low-P oils. Using two acid soils, Acrisols and Andosols, two experiments were carried out to evaluate the effect of Minjingu PR on the growth of four agroforestry multipurpose trees, Leucaena leucocephala, Cenna siamea, Grevillea robusta, and Eucalyptus grandis. Results of the first two experiments are reported. In the first experiment, 1-month-old seedlings received Minjingu PR at rates of 0 (PRo), 52 (PR_1) and 77 (PR_2) kg P/ha in lots of 2 kg soil. In the second experiment, the Minjingu PR rates of the first experiment were maintained and G. robusta and L. leucocephala were grown. In this experiment only an Acrisol was used. There was a slower response to Minjingu PR fertilizer application in Andosols compared with Acrisols. At 19 weeks after transplanting, PR_2 had caused a significant (p <0.05) height increase over PRo in L. euco cephala, and both the height and the root collar diameter increased in the case of G robusta grown on Acrisols. Addition of PR_2 had a negative effect on height of C. siamea, whereas E. grandis did not respond to PR additions. In the second study, there were significant increases of up to 121% in height (p <0.001) and root collar diameter (p <0.05) and 4.5 times biomass over the controls where L. leucocephala seedlings received PR only and PR + mycorrhizae at 12 months after planting (months after transplant-ing). Nodulation of L. leucocephala was significantly affected by P application and/or AM inoculation but was variable within treatments except for controls. Species x treatments interactions were significant at p <0.05 and p<0.001 for shoot and root dry weight, respectively. Phosphate rock and mycor-rhizae inoculation have the potential to improve legume performance in these acidic soils.
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