The comparative phosphorus requirements of some temperate perennial legumes.
P responses of Lupinus polyphyllus, L. arboreus and 7 temperate perennial pasture legumes were compared in a field trial over a range of 9 P rates, from 0 to 800 kg/ha. Lupinus spp. produced more than 5 t DM/ha in the absence of added P and showed no response to fertilizer. In contrast, the pasture legumes initially failed to grow without added P and responded to applications of between 200 and 800 kg/ha. At the higher P rates, DM production of pasture legumes was equivalent to that of Lupinus spp. In the first 2 years of the trial, the most productive pasture legume species at the higher rates of added P were also the most productive at the lower rates. P requirements for 90% of max. yield varied greatly between species, but were closely related to max. yield. Thus species with low P requirements for max. yield were not necessarily P-efficient species. In the third and subsequent years of the trial Lotus corniculatus performed better than the other pasture legumes at the lower rates of added P. In contrast to other studies Lotus pedunculatus [L. uliginosus] showed no ability to outyield Trifolium repens at low rates of P. Critical P concn of the pasture species for the late spring-early summer period declined in the order T. repens (0.34%) > L. pedunculatus (0.30%) > T. pratense (0.28%) > T. hybridum (0.27%) > T. ambiguum (0.26%) > L. corniculatus (0.23%). Mineralizable N levels were determined in soils under 3 species in the 7th year of the trial. At the lowest rates of added P, mineralizable N levels were much higher under L. polyphyllus than under T. repens or L. corniculatus. With increasing P rate, levels under the latter species increased, and at 100 kg P/ha were equivalent to those under L. polyphyllus with no added P.