Uptake of soil nitrogen by legumes in mixed swards

摘要: The partitioning of uptake soil nitrogen between legumes and grasses in mown, mixed swards was studied at two sites south-eastern Queensland. contained either Lotononis bainesii, Desmodium intortum or Trifolium repens with Digitaria decumbens one site, L. T. repens, Macroptilium atropurpureum, Vigna luteola Stylosanthes guyanensis Chloris gayana the other site. (15NH4)2SO4 equivalent to c. 0.3 kg ha-1 added every 4 weeks an attempt label mineral nitrogen, 15N species used as estimate nitrogen. Although (L. bainesii repens) obtained 70–100% total some spring harvests, when growth associated tropical limited by low temperatures, none more than 25% annual over a 2-year period. Proportional curvilinearly related proportion legume dry matter yield mixtures. Annual grass-legume mixtures up 360% high grass control. This had only small effect on estimates derived from symbiotic fixation, but caused large discrepancy isotopic transfer. fixed averaged 94% site 92% other, nearly always exceeded 80%, independent yield.