Phosphorus efficient pastures: response of alternative legumes to fertiliser application

There is interest in pastures that require less phosphorus (P) fertilizer because P costs have risen. This objective requires legumes that yield as well as Trifolium subterraneum, but with lower critical P requirements (rate of fertilizer for 90% of maximum yield).
Two field sites were sown near Yass (autumn, 2012) and Bookham (2013). Yass was re-sown in 2013 to ensure establishment did not limit dry matter (DM) responses to P. The experiments included 12 pasture species (monocultures) at 6 P rates (0-80 kg P/ha, as triple superphosphate), (n=3 replicates). Maintenance P (0-31 kg P/ha) was applied at Yass in 2013. Lime and basal nutrients were applied to ensure only P and nitrogen were limiting. Legumes were inoculated with appropriate rhizobia. Herbage DM was determined in spring. Mitscherlich equations fitted to the DM data after Linear Mixed Model analysis were used to compare P requirements.
Some species proved unsuited to the soils and climate. Of those that established and grew well, only the grasses (Phalaris aquatica, Dactylis glomerata) and three legumes (Ornithopus sativus [pasture type], T. incarnatum, T. purpureum [forage types]) had DM yields equivalent to, or better than T. subterraneum whilst also having lower P-fertiliser requirements. O. compressus required less P, but did not yield as well. The critical P requirement of Medicago sativa was not reached over the P range used.
The experiments demonstrated that the P requirements of pasture legumes can differ. A few species yielded as well as T. subterraneum with lower critical P requirements.