Legumes increase grassland productivity with no effect on nitrous oxide emissions

Abstract

Aims Grasslands 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. Methods This 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 aboveand below-ground biomass, shoot N uptake, soil physico-chemical properties and GHG emissions. Results Above-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 N 2 O emissions, total soil N or mineral-N in fertilised or unfertilised soils. Conclusions This 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.

Evaluating the Potential of Legumes to Mitigate N2O Emissions From Permanent Grassland Using Process‐Based Models

“…However, in a recent field experiment at Site G5 (Fuchs et al, 2018), N 2 O‐Int was reduced from 0.42 g N kg DM −1 yr −1 on a fertilized control obtaining fertilizer N via slurry (240 kg N, 4–15% clover) to 0.28 g N kg DM −1 yr −1 at the clover treatment (23–40% clover and no N fert ) over a 2‐year observation period. Further, lab experiments by Barneze et al (2019) confirmed the model results that higher clover proportions increase productivity without affecting N 2 O emissions, resulting in reduced N 2 O‐Int.…”

Nitrous Oxide Emission from Grazing Is Low across a Gradient of Plant Functional Diversity and Soil Conditions

“…Similarly, Niklaus et al [59] reported a significant legume effect on N 2 O emission. On the contrary, Barneze et al [65] found no legume effect on N 2 O emission, total mineral N or mineral N in fertilized or unfertilized soils.…”

“…Under monoculture, legumes appeared to emit more N 2 O than other species [59]. However, this might not be necessarily additive in mixed pastures [66], but increases in the proportion of legumes might influence C and N cycling processes [65]. This legume effect on N 2 O emission might be related to the increased N supply (Table 3), leading to nitrification and denitrification losses.…”

“…This legume effect on N 2 O emission might be related to the increased N supply (Table 3), leading to nitrification and denitrification losses. Therefore, the increased NO 3 availability due to the release of fixed N from legume roots via decomposition and legumes' inefficiency in acquiring mineral N [65] may explain the high association of legumes with the N 2 O emission. The inclusion of legumes in mixed-swards at proportions of 30-50% is described as most effective, providing multiple outputs including reduced greenhouse gas emission, higher productivity and increased protein self-sufficiency, and reduced N leaching [48,67].…”

Clover in agriculture: combined benefits for bees, environment, and farmer

“…Trials in the UK have shown that grass plus red clover swards utilise available nutrients more efficiently than grass monocultures, contributing to increased yield of subsequently planted cereals (Doel 2013). Grass plus red clover swards have also been found to increase production of above ground biomass, dry matter yield, and digestible organic matter compared to grass monocultures (de Haas et al 2019;Barneze et al 2020). However, despite improving dry matter yield when grown in a grass mixture compared with grass monocultures (de Haas et al 2019;Barneze et al 2020), red clover is not as well suited to grazing as white clover due to lower production potential in grazed swards and is, therefore, grown more for silage for winter feeding of ruminants (Frankow-Lindberg 2017).…”