title: Nitrogen yield advantage from grass-legume mixtures is robust over a wide range of legume proportions and environmental conditions.
abstract: Current challenges to global food security require sustainable intensification of agriculture through initiatives that include more efficient use of nitrogen (N), increased protein self-sufficiency through homegrown crops, and reduced N losses to the environment. Such challenges were addressed in a continental-scale field experiment conducted over 3 years, in which the amount of total nitrogen yield (Ntot ) and the gain of N yield in mixtures as compared to grass monocultures (Ngainmix ) was quantified from four-species grass-legume stands with greatly varying legume proportions. Stands consisted of monocultures and mixtures of two N2 -fixing legumes and two nonfixing grasses. The amount of Ntot of mixtures was significantly greater (P ≤ 0.05) than that of grass monocultures at the majority of evaluated sites in all 3 years. Ntot and thus Ngainmix increased with increasing legume proportion up to one-third of legumes. With higher legume percentages, Ntot and Ngainmix did not continue to increase. Thus, across sites and years, mixtures with one-third proportion of legumes attained ~95% of the maximum Ntot acquired by any stand and had 57% higher Ntot than grass monocultures. Realized legume proportion in stands and the relative N gain in mixture (Ngainmix /Ntot in mixture) were most severely impaired by minimum site temperature (R = 0.70, P = 0.003 for legume proportion; R = 0.64, P = 0.010 for Ngainmix /Ntot in mixture). Nevertheless, the relative N gain in mixture was not correlated to site productivity (P = 0.500), suggesting that, within climatic restrictions, balanced grass-legume mixtures can benefit from comparable relative gains in N yield across largely differing productivity levels. We conclude that the use of grass-legume mixtures can substantially contribute to resource-efficient agricultural grassland systems over a wide range of productivity levels, implying important savings in N fertilizers and thus greenhouse gas emissions and a considerable potential for climate change mitigation.
authors: Institute for Sustainability Sciences ISS, Agroscope, Reckenholzstrasse, 8046 Zürich, Switzerland.
authors: Matthias
authors: M
authors: Suter
authors: John
authors: J
authors: Connolly
authors: John A
authors: JA
authors: Finn
authors: Ralf
authors: R
authors: Loges
authors: Laura
authors: L
authors: Kirwan
authors: Maria-Teresa
authors: MT
authors: Sebastià
authors: Andreas
authors: A
authors: Lüscher
mesh_terms: D002980:Climate; D005060:Europe; D007887:Fabaceae / Q000378:metabolism*; D065948:Grassland; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D006109:Poaceae / Q000378:metabolism*; D013696:Temperature
chemical_list: D009584:Nitrogen
keywords: N fertilizer replacement; N uptake; climate change mitigation; climatic gradient; food security; protein; sustainable agriculture; sustainable intensification; symbiotic N2 fixation