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Intrinsic capacity for nutrient foraging predicts critical external phosphorus requirement of 12 pasture legumes
The mainstream pasture legume species (i.e. Trifolium subterraneum, T. repens and annual Medicago spp.) used in the temperate pasture systems of southern Australia have high critical external requirements for phosphorus (P) (i.e. P required to achieve 90% of maximum yield). This work aimed to identify alternative pasture legume species that could be used in lower P-input systems. Shoot and root biomass of 12 pasture legume species was measured in response to 7 rates of P applied to the top 48 mm of soil in a pot experiment. Most species had similar maximum yields to T. subterraneum, but some required only a third of the applied P to achieve this. The critical external P requirement of the species ranked from lowest to highest was as follows: Ornithopus compressus = O. sativus < Biserrula pelecinus < T. michelianum = T. vesiculosum = T. glanduliferum < T. hirtum = Medicago truncatula = T. purpureum = T. incarnatum < T. spumosum = T. subterraneum. An ability to efficiently maximise soil exploration through a combination of high root length density, high specific root length and long root hairs (i.e. a large specific root hair cylinder volume) was associated with a low critical external P requirement. The results indicate that Ornithopus spp. could be used to achieve productive, low P-input pasture systems.
CP17276 Accepted 07 November 2017
© CSIRO 2017