Abstract
AimsGrasslands are important agricultural production systems, where ecosystem functioning is affected by land management practices. Grass-legume mixtures are commonly cultivated to increase grassland productivity while reducing the need for nitrogen (N) fertiliser. However, little is known about the effect of this increase in productivity on greenhouse gas (GHG) emissions in grass-legume mixtures. The aim of this study was to investigate interactions between the proportion of legumes in grass-legume mixtures and N-fertiliser addition on productivity and GHG emissions. We tested the hypotheses that an increase in the relative proportion of legumes would increase plant productivity and decrease GHG emissions, and the magnitude of these effects would be reduced by N-fertiliser addition.MethodsThis was tested in a controlled environment mesocosm experiment with one grass and one legume species grown in mixtures in different proportions, with or without N-fertiliser. The effects on N cycling processes were assessed by measurement of above- and below-ground biomass, shoot N uptake, soil physico-chemical properties and GHG emissions.ResultsAbove-ground productivity and shoot N uptake were greater in legume-grass mixtures compared to grass or legume monocultures, in fertilised and unfertilised soils. However, we found no effect of legume proportion on N2O emissions, total soil N or mineral-N in fertilised or unfertilised soils.ConclusionsThis study shows that the inclusion of legumes in grass-legume mixtures positively affected productivity, however N cycle were in the short-term unaffected and mainly affected by nitrogen fertilisation. Legumes can be used in grassland management strategies to mitigate climate change by reducing crop demand for N-fertilisers.
Highlights
This study shows that the inclusion of legumes in grass-legume mixtures positively affected productivity, N cycle were in the short-term unaffected and mainly affected by nitrogen fertilisation
To quantify the interactive effects of N fertiliser and grass-legume mixtures on C and N cycling, a fastgrowing legume species, Trifolium pratense L. (Tr), and a grass species, Agrostis capillaris L., were selected (Emorsgate Seeds, Kings Lynn, UK), both of which commonly occur in managed temperate grasslands across Europe
Five grass-legume mixtures with 0, 25%, 50%, 75% and 100% legume abundance were superimposed with N addition treatment resulting in 10 treatments in total
Summary
These include sequestering carbon (C) in plant biomass and soil organic matter, and producing the majority of forage for ruminants (De Deyn et al 2008). Grassland species composition has been shown to be an important driver of these ecosystems functions (Bardgett 2011; De Deyn et al 2009; Loreau and Hector 2001; Tilman et al 2001) due to plant-plant and plantsoil interactions. The use of mixtures has been shown to increase plant productivity through increases in resource uptake efficiency due to: i) N transfer from legumes to grasses (Høgh-Jensen and Schjoerring 1997; Pirhofer-Walzl et al 2012), and/or ii) species differences in root structure increasing the exploitation of soil resources (Mueller et al 2013; van Ruijven and Berendse 2005). Legume-based cropping can reduce N losses from soil via leaching (Drinkwater et al 1998; Li et al 2016) and increase C sequestration due to increased plant C inputs (De Deyn et al 2011)
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