Publication: nitrogen yield advantage from grass-legume mixtures

Nitrogen yield advantage from grass-legume mixtures is robust over a wide range of legume proportions and environmental conditions

Our latest publication from our international collaboration COST Action 852 is in Global Change Biology, lead by Matthias Suter of Agroscope in Switzerland. In it, Matthias used data on total nitrogen yield from 16 international sites to investigate whether four-species (two grasses, red clover, white clover) grass-legume mixtures can deliver more nitrogen in forage per unit area (it did). We also investigated whether this benefit was related to the % of clover in the sward - it was and it wasn't (!), but only because the benefit plateaued at a clover proportion of about 33% in the sward.  

Main conclusions
•Higher N output (55% more Ntot or forage protein per unit area) can be achieved with grass-legume mixtures than with grass alone for a given amount of N fertilizer applied.
•The use of grass-legume mixtures can substantially contribute to resource-efficient agricultural grassland systems, implying important savings in N fertilizers and greenhouse gas emissions.

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 home-grown crops, and reduced N losses to the environment. Such challenges were addressed in a continental-scale field experiment conducted over three years, in which the amount of total nitrogen yield (N_tot) and the gain of N yield in mixtures as compared to grass monocultures (N_gainmix) 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 non-fixing grasses.The amount of N_tot of mixtures was significantly greater (P ≤ 0.05) than that of grass monocultures at the majority of evaluated sites in all three years. N_tot and thus N_gainmix increased with increasing legume proportion up to one third of legumes. With higher legume percentages, N_tot and N_gainmix did not continue to increase. Thus, across sites and years, mixtures with one third proportion of legumes attained ~95% of the maximum N_tot acquired by any stand and had 57% higher N_tot than grass monocultures.Realized legume proportion in stands and the relative N gain in mixture (N_gainmix/N_tot 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 N_gainmix/N_tot 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: M Suter, J. Connolly, J.A Finn, R Loges, L Kirwan, M. T Sebastià and A Lüscher

DOI: 10.1111/gcb.12880

Part of the research leading to these results has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement n° 266018

 

Related publications
Suter M, Connolly J, Finn JA, Loges R, Kirwan L, Sebastià MT, Lüscher A (2015) Nitrogen yield advantage fromgrass-legume mixtures is robust over a wide range of legume proportions and environmental conditions. Global Change Biology, in press.
 

Kirwan et al. 2014. The Agrodiversity Experiment:three years of data from a multi-site plant diversity experiment in intensivelymanaged grasslands. Ecological Archives, 95: 2680.
 

Finn,et al. (2013), Ecosystem function enhanced by combining four functional types of plant species in intensively managed grassland mixtures: a 3-year continental-scale fieldexperiment. Journal of Applied Ecology, 50: 365–375.