Article (Scientific journals)
Herd position habits can bias net CO2 ecosystem exchange estimates in free range grazed pastures.
Gourlez de la Motte, Louis; Dumortier, Pierre; Beckers, Yves et al.
2019In Agricultural and Forest Meteorology, 268
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Keywords :
Eddy covariance; grazing; grassland; methane; CO2; NEE
Abstract :
[en] The eddy covariance (EC) technique has been widely used to quantify the net CO2 ecosystem exchange (NEE) of grasslands, which is an important component of grassland carbon and greenhouse gas budgets. In free range grazed pastures, NEE estimations are supposed to also include cattle respiration. However, cattle respiration measurement by an EC system is challenging as animals act as moving points emitting CO2 that are more or less captured by the EC tower depending on their presence in the footprint. Often it is supposed that, over the long term, cattle distribution in the pasture is homogeneous so that fluctuations due to moving sources are averaged and NEE estimates are reasonably representative of cattle respiration. In this study, we test this hypothesis by comparing daily cow respiration rate per livestock unit (LU) estimated by postulating a homogeneous cow repartition over the whole pasture with three other estimates based on animal localization data, animal scale carbon budget and confinement experiments. We applied these methods to an intensively managed free range grassland and showed that the NEE estimate based on a homogeneous cow repartition was systematically lower than the three other estimates. The bias was about 60 g C m–2 yr–1, which corresponded to around 40% of the annual NEE. The sign and the importance of this bias is site specific, as it depends on cow location habits in relation to the footprint of the EC measurements which highlight the importance of testing the hypothesis of homogeneity of cattle distribution on each site. Consequently, in order to allow estimating the validity of this hypothesis but also to improve inter site comparisons, we advocate to compute separately pasture NEE and grazer’s respiration. For the former we propose a method based on cattle presence detection using CH4 fluxes, elimination of data with cattle and gap filling on the basis of data without cattle. For the second we present and discuss three independent methods (animal localization with GPS, animal scale carbon budget, confinement experiments) to estimate the cattle respiration rate.
Research center :
TERRA Teaching and Research Centre - TERRA
Disciplines :
Agriculture & agronomy
Author, co-author :
Gourlez de la Motte, Louis ;  Université de Liège - ULiège > Ingénierie des biosystèmes (Biose) > Biosystems Dynamics and Exchanges
Dumortier, Pierre ;  Université de Liège - ULiège > Ingénierie des biosystèmes (Biose) > Biosystems Dynamics and Exchanges
Beckers, Yves  ;  Université de Liège - ULiège > Agronomie, Bio-ingénierie et Chimie (AgroBioChem) > Ingénierie des productions animales et nutrition
Bodson, Bernard ;  Université de Liège - ULiège > Agronomie, Bio-ingénierie et Chimie (AgroBioChem) > Ingénierie des productions végétales et valorisation
Heinesch, Bernard  ;  Université de Liège - ULiège > Ingénierie des biosystèmes (Biose) > Biosystems Dynamics and Exchanges
Aubinet, Marc ;  Université de Liège - ULiège > Ingénierie des biosystèmes (Biose) > Biosystems Dynamics and Exchanges
Language :
English
Title :
Herd position habits can bias net CO2 ecosystem exchange estimates in free range grazed pastures.
Publication date :
2019
Journal title :
Agricultural and Forest Meteorology
ISSN :
0168-1923
eISSN :
1873-2240
Publisher :
Elsevier, Netherlands
Volume :
268
Peer reviewed :
Peer Reviewed verified by ORBi
Name of the research project :
Bilan carbone d'une exploitation
Funders :
SPW DG03-DGARNE - Service Public de Wallonie. Direction Générale Opérationnelle Agriculture, Ressources naturelles et Environnement [BE]
Commentary :
Établissement du bilan de carbone d’une exploitation agricole wallonne pratiquant le système allaitant : effets du climat et de la gestion des pâturages
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since 22 February 2019

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