Premier Digit and Progardes Desmanthus compete effectively for applied phosphorus under mixed sward conditions

Grasses generally dominate the pastures of northern Australia. This may be associated, in part, with varietal differences in critical phosphorus (P) requirements that influence the competitive ability and persistence of the legume component. However, the effect of plant competition on shoot yield responses to soil P supply remain unquantified in tropical pasture swards. Micro-swards of Premier Digit and Progardes Desmanthus were grown, both as monocultures and mixed plantings, in soil amended with five rates of P fertiliser to determine the influence of sward conditions on shoot yield and tissue P. The shoot yield and tissue P concentrations of both species increased in response to soil P supply, with the shoot yield of Progardes Desmanthus in mixed plantings representing between 33–47% of the total yield of Digit and Desmanthus combined. The critical external P requirements of Progardes Desmanthus were generally equal to or lower than that of Premier Digit, yet both species competed effectively for applied P. Therefore, Premier Digit and Progardes Desmanthus may be suitable companion pasture species for establishment in the low-P soils of northern Australia.