Comparative effects of rock phosphates on arbuscular mycorrhizal colonization of Trifolium pratense L.

The effect of five rock phosphates with different solubility (from Algeria, North Florida, North Carolina, Senegal, and Morocco) and that of single superphosphate (SSP) alone or with lime was investigated on the root colonization of red clover with indigenous arbuscular mycorrhizal fungi (AMF). In a pot experiment, the phosphorus (P) sources were applied at four rates (0, 100, 400, and 1600 mg total P2O5 kg(-1) dry soil) to an acidic sandy soil (Nyirlugos) and to an acidic clay loam soil (Ragaly). The arbuscule content of the roots was more sensitive to various rock phosphates than the infection frequency. No mycorrhizal colonization of roots was observed in the Nyirlugos soil at the 1600 mg P2O5 kg(-1) level of SSP or in either soil at the 1600 mg P2O5 kg(-1) level of SSP+lime, indicating that the mycorrhizal dependency of the host was eliminated by the highest soluble P concentrations in the soil.