The annual ammonia budget of fertilised cut grassland – Part 1: Micrometeorological flux measurements and emissions after slurry application

C Spirig,A Neftel,C R Flechard,C Ammann

doi:10.5194/bg-7-521-2010

C Spirig, A Neftel + Show 2 more

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https://doi.org/10.5194/bg-7-521-2010

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Abstract

Abstract. Two commercial ammonia (NH3) analysers were customised to allow continuous measurements of vertical concentration gradients. The gradients were used to derive ammonia exchange fluxes above a managed grassland site at Oensingen (Switzerland) by application of the aerodynamic gradient method. The measurements from July 2006 to October 2007 covered five complete growth-cut cycles and included six applications of liquid cattle slurry. The average accuracy of the flux measurements during unstable and near-neutral conditions was 20% and the detection limit was 10 ng NH3 m−2 s−1. Hence the flux measurements are considered sufficiently accurate for studying typical NH3 deposition rates over growing vegetation. Quantifying the overall emissions after slurry applications required the application of elaborate interpolations because of difficulties capturing the initial emissions during broadspreading of liquid manure. The emissions were also calculated with a mass balance method yielding similar fluxes. NH3 losses after slurry application expressed as percentage of emitted nitrogen versus applied total ammoniacal nitrogen (TAN) varied between 4 and 19%, which is roughly a factor of three lower than the values for broadspreading of liquid manure in emission inventories. The comparatively low emission factors appear to be a consequence of the low dry matter content of the applied slurry and soil properties favouring ammonium adsorption.

Highlights

Ammonia (NH3) is the most abundant alkaline substance in the atmosphere and has been recognised as a key player in processes leading to formation of particulate matter (e.g. Hayes et al, 1980; Kulmala et al, 2002; Erisman and Schaap, 2004; Vayenas et al, 2005; Yu, 2006) and eutrophication and acidification of ecosystems (Erisman et al, 2007)
In this paper we explore to what extent aerodynamic gradient method (AGM) measurements can be used to quantify emissions after slurry applications and discuss methodical aspects of our gradient measurement system
The MAGS was suitable for measuring ammonia exchange fluxes over a managed grassland site at 15–30 min time resolution during two consecutive years

Summary

Introduction

Ammonia (NH3) is the most abundant alkaline substance in the atmosphere and has been recognised as a key player in processes leading to formation of particulate matter (e.g. Hayes et al, 1980; Kulmala et al, 2002; Erisman and Schaap, 2004; Vayenas et al, 2005; Yu, 2006) and eutrophication and acidification of ecosystems (Erisman et al, 2007). Agriculture represents the dominant NH3 source at global and national levels (Reidy et al, 2008; Spranger et al, 2009), with emissions occurring as part of animal husbandry, during manure storage and following the land spreading of organic wastes for fertilisation. Both agricultural and natural vegetation generally act as sinks for atmospheric NH3, as it is efficiently deposited on almost any kind of surface, when they are wet. Given the prominent role of agriculture in controlling the atmospheric abundance of NH3, a better mechanistic understanding of its exchange over agricultural surfaces is required for accurately describing source–receptor relationships (Achermann and Bobbink, 2003)

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