Large Variations in N2O Fluxes from Bioenergy Crops According to Management Practices and Crop Type

Fabien Ferchaud,Céline Peyrard,Bruno Mary,Joël Léonard,Eric Gréhan

doi:10.3390/atmos11060675

Abstract

Field N2O emissions are a key point in the evaluation of the greenhouse gas benefits of bioenergy crops. The aim of this study was to investigate N2O fluxes from perennial (miscanthus and switchgrass), semi-perennial (fescue and alfalfa) and annual (sorghum and triticale) bioenergy crops and to analyze the effect of the management of perennials (nitrogen fertilization and/or harvest date). Daily N2O emissions were measured quasi-continuously during at least two years in a long-term experiment, using automated chambers, with 2–5 treatments monitored simultaneously. Cumulative N2O emissions from perennials were strongly affected by management practices: fertilized miscanthus harvested early and unfertilized miscanthus harvested late had systematically much lower emissions than fertilized miscanthus harvested late (50, 160 and 1470 g N2O-N ha−1 year−1, respectively). Fertilized perennials often had similar or higher cumulative emissions than semi-perennial or annual crops. Fluxes from perennial and semi-perennial crops were characterized by long periods with low emissions interspersed with short periods with high emissions. Temperature, water-filled pore space and soil nitrates affected daily emissions but their influence varied between crop types. This study shows the complex interaction between crop type, crop management and climate, which results in large variations in N2O fluxes for a given site.

Highlights

Nitrous oxide (N2 O) is a potent greenhouse gas (GHG), with a 100-year global warming potential of 265–298 CO2 equivalents [1]
We focused on nine treatments, which were chosen to explore N2 O emissions of a diversity of crop types, as well as the effect of management practices for perennial crops (Table 1): three treatments with miscanthus, two with switchgrass, two with semi-perennial crops and two with annual crops
It should be mentioned that the difference in soil characteristics between paired plots was similar to the variability observed over the whole set of 15 plots used for N2 O monitoring during the study (Table S2) and that the dynamics of daily N2 O emissions was very similar both between chambers in a given plot and between paired plots

Summary

Introduction

Nitrous oxide (N2 O) is a potent greenhouse gas (GHG), with a 100-year global warming potential of 265–298 CO2 equivalents [1]. Its atmospheric concentration has increased by 20% since pre-industrial times and N2 O represented 6.2% of the total anthropogenic GHG emissions in 2010 [1]. N2 O is currently the most important ozone-depleting substance after the success of the Montreal Protocol to regulate the emissions of chlorofluorocarbons [2]. Agriculture is the largest anthropogenic source of. Reducing N2 O emissions from agricultural soils is an important element of climate change mitigation and ozone protection strategies [4]. N2 O emissions from soils predominantly originate from two microbial processes [5]: nitrification (oxidation of ammonium to nitrite and nitrate), which occurs under aerobic conditions, and denitrification (reduction of nitrate to N2 ), taking place in anaerobic conditions. Because the availability of mineral nitrogen (N) is a major driver of N2 O soil emissions, Atmosphere 2020, 11, 675; doi:10.3390/atmos11060675 www.mdpi.com/journal/atmosphere

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