Publication Date:
2015-01-29
Description:
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 N 2 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. This article is protected by copyright. All rights reserved.
Print ISSN:
1354-1013
Electronic ISSN:
1365-2486
Topics:
Biology
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Energy, Environment Protection, Nuclear Power Engineering
,
Geography
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