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See detailDiurnal and seasonal variability of CO2 fluxes over a degraded Woodland under a Sudanian climate in Northern Benin (West Africa)
Ago, Expédit Evariste; Serça, Dominique; Agbossou, Euloge Kossi et al

in Geophysical Research Abstracts (2015, April), 17

Turbulent CO2 exchanges over a degraded woodland were measured during 17 months (from November 2005 to March 2007) by an eddy-covariance system at Nangatchori in the northern part of Benin, West Africa ... [more ▼]

Turbulent CO2 exchanges over a degraded woodland were measured during 17 months (from November 2005 to March 2007) by an eddy-covariance system at Nangatchori in the northern part of Benin, West Africa. The site (Lat 9.65°N, Long 1.74°E, Alt: 432 m), under a Sudanian climate, is one of the sites that were equipped in the framework of the international AMMA-CATH program. The site was highly disturbed during preceding years by illegal tree logging, agricultural activities, cattle pasture, and bushfire. The footprint area is mainly formed by herbs and crops with some sparse shrubs and trees. Fluxes data were completed during the same period by meteorological measurements made at the Nalohou site located approximately 20 km from Nangatchori, and by an inventory of dominating species on 1km2 area around the tower during the wet season. Fluxes response to climatic variables was analyzed. The annual drought and moisture cycle was found to be the main controlling factor of the ecosystem dynamics. A very clear response of CO2 fluxes to PPFD appears, but is different according to seasons. During wet season, CO2 uptake increases with increasing PPFD following a typical curvilinear function and saturates for high PPFD (PPFD > 1000 µmol m-2 s-1), while during dry season, a very weak linear response of CO2 fluxes was observed. No clear dependency of the total ecosystem respiration on temperature was observed. At an annual scale (from November 1st 2005 to October 31st 2006), net carbon sequestered by the ecosystem was 18 +- 5 g C m-2. Finally, with respect to the water use the ecosystem appeared to be more efficient during morning and wet season than during afternoon and dry period. [less ▲]

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See detailThe CROSTVOC project – an integrated approach to study the effect of stress on BVOC exchange between agricultural crops and grassland ecosystems and the atmosphere
Amelynck, Crist; Heinesch, Bernard ULg; Aubinet, Marc ULg et al

in Geophysical Research Abstracts (2015, April), 17

Global changes in atmospheric composition and climate are expected to affect BVOC exchange between terrestrial vegetation and the atmosphere through changes in the drivers of constitutive BVOC emissions ... [more ▼]

Global changes in atmospheric composition and climate are expected to affect BVOC exchange between terrestrial vegetation and the atmosphere through changes in the drivers of constitutive BVOC emissions and by increases in frequency and intensity of biotic or abiotic stress episodes. Indeed, several studies indicate changes in the emission patterns of constitutive BVOCs and emission of stress-induced BVOCs following heat, drought and oxidative stress, amongst others. Relating changes in BVOC emissions to the occurrence of one or multiple stressors in natural environmental conditions is not straightforward and only few field studies have dealt with it, especially for agricultural crop and grassland ecosystems. The CROSTVOC project aims to contribute in filling this knowledge gap in three ways. Firstly, it aims at performing long-term BVOC emission field measurements from maize (Zea mays L.) and wheat (Triticum aestivum L.), two important crop species on the global scale, and from grassland. This should lead to a better characterization of (mainly oxygenated) BVOC emissions from these understudied ecosystems, allowing a better representation of those emissions in air quality and atmospheric chemistry and transport models. BVOC fluxes are obtained by the Disjunct Eddy Covariance by mass scanning (DEC-MS) technique, using a hs-PTR-MS instrument for BVOC analysis. Secondly, the eddy covariance BVOC flux measurements (especially at the grassland site) will be accompanied by ozone flux, chlorophyll fluorescence, photosynthesis and soil moisture measurements, amongst others, to allow linking alterations in BVOC emissions to stress episodes. Simultaneously, automated dynamic enclosures will be deployed in order to detect specific abiotic and biotic stress markers by PTR-MS and identify them unambiguously by GC-MS. Thirdly, the field measurements will be accompanied by laboratory BVOC flux measurements in an environmental chamber in order to better disentangle the responses of the BVOC emissions to driving factors that co-occur in field conditions and to determine the influence of single abiotic stressors on BVOC emissions. Next to a general presentation, some preliminary results of the project will be shown. [less ▲]

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See detailMeasuring and modelling the intra-day variability of the CO2 & CO2 vertical soil profile production in a Scots pine forest
Longdoz, Bernard; Goffin, Stéphanie; Parent, Florian et al

in Geophysical Research Abstracts (2015, April), 17

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See detailBiogenic Volatile Organic Compound (BVOC) emissions from agricultural crop species: is guttation a possible source for methanol emissions following light/dark transition?
Mozaffar, Ahsan ULg; Amelynck, Crist; Bachy, Aurélie ULg et al

in Geophysical Research Abstracts (2015, April), 17(EGU2015-2110-1),

In the framework of the CROSTVOC (CROp STress VOC) project, the exchange of biogenic volatile organic compounds (BVOCs) between two important agricultural crop species, maize and winter wheat, and the ... [more ▼]

In the framework of the CROSTVOC (CROp STress VOC) project, the exchange of biogenic volatile organic compounds (BVOCs) between two important agricultural crop species, maize and winter wheat, and the atmosphere has recently been measured during an entire growing season by using the eddy covariance technique. Because of the co-variation of BVOC emission drivers in field conditions, laboratory studies were initiated in an environmental chamber in order to disentangle the responses of the emissions to variations of the individual environmental parameters (such as PPFD and temperature) and to diverse abiotic stress factors. Young plants were enclosed in transparent all-Teflon dynamic enclosures (cuvettes) through which BVOC-free and RH-controlled air was sent. BVOC enriched air was subsequently sampled from the plant cuvettes and an empty cuvette (background) and analyzed for BVOCs in a high sensitivity Proton-Transfer Reaction Mass Spectrometer (hs-PTR-MS) and for CO2 in a LI-7000 non-dispersive IR gas analyzer. Emissions were monitored at constant temperature (25 °C) and at a stepwise varying PPFD pattern (0-650 µmol m-2 s-1). For maize plants, sudden light/dark transitions at the end of the photoperiod were accompanied by prompt and considerable increases in methanol (m/z 33) and water vapor (m/z 39) emissions. Moreover, guttation droplets appeared on the sides and the tips of the leaves within a few minutes after light/dark transition. Therefore the assumption has been raised that methanol is also coming out with guttation fluid from the leaves. Consequently, guttation fluid was collected from young maize and wheat plants, injected in an empty enclosure and sampled by PTR-MS. Methanol and a large number of other compounds were observed from guttation fluid. Recent studies have shown that guttation from agricultural crops frequently occurs in field conditions. Further research is required to find out the source strength of methanol emissions by this guttation phenomenon in real environmental conditions. [less ▲]

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See detailNitrous oxide flux measurement with a closed chamber system : data treatment
Regaert, Donat ULg; Moureaux, Christine ULg; Heinesch, Bernard ULg et al

Poster (2015, January 30)

Nitrous oxide flux estimation from concentration measurements with a closed chamber system. Statistical data treatment to sort between relevant/irrelevant fluxes.

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See detailCarbon balance of a grazed pasture and its response to grazing management
Jerome, Elisabeth ULg; Gourlez de la Motte, Louis ULg; Beckers, Yves et al

Poster (2014, September 24)

The C balance of a grazed pasture situated in Condroz (Wallonia) and its dependence on climatic conditions and grazing management were investigated on the basis of eddy covariance measurements and ... [more ▼]

The C balance of a grazed pasture situated in Condroz (Wallonia) and its dependence on climatic conditions and grazing management were investigated on the basis of eddy covariance measurements and horizontal C flow estimates. In average on three years, NEE was +43±24 gCm-2yr-1 and NBP was +7±26 gCm-2yr-1, suggesting that that the site is C neutral. Management by the farmer (organic fertilization), but also climate conditions influencing management (feed supplements), were the main factors impacting the C balance inter-annual variability. At a daily and seasonal scale, grazing impact on CO2 fluxes did not appear explicitly, being blurred by flux response to climate drivers. It was highlighted by specific investigations. The indirect grazing impact (photosynthesizing biomass consumption, excretions, soil compaction) was deduced from an analysis of the flux to PPFD response evolution during grazing period; the direct impact (livestock respiration) was investigated through confinement experiments. Result showed that saturation GPP changes were negatively correlated to grazing intensity (product of the stocking rate and grazing duration). On the contrary, no significant change in TER was observed. The direct impact of grazing due to cattle respiration was estimated to 2.59±0.58 kgCLU-1day-1, i.e. 8% of the TER. [less ▲]

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See detailAre agricultural ecosystems important BVOC « exchangers »? Evidences from 2 measurement years on croplands at Lonzée Terrestrial Observatory (Belgium)
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

Poster (2014, September 23)

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile ... [more ▼]

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile Organic Compounds) emission from terrestrial ecosystems. Indeed, those compounds which are mostly emitted by plants play a great role in the atmospheric chemistry, thereby influencing the Earth surface radiative budget and the tropospheric air quality. However, so far, very few is known about BVOC exchange by crops, implying that huge uncertainties remain about qualifying, quantifying and determining sources/sinks and driving mechanisms of BVOC exchanges between croplands ecosystems and the atmosphere. We present here the first long term BVOC fluxes measurement study conducted on maize (2012) and winter wheat (2013), respectively the second and first most important worldwide crops (FAOSTAT). BVOC exchange was measured using the disjunct by mass scanning eddy covariance technique (+ PTR-MS, Ionicon) at the Lonzée Terrestrial Observatory (ICOS site) in Belgium. Main results are: (i) crops emit mainly methanol; (ii) BVOC emission from studied crops is lower than in literature, suggesting that agricultural ecosystems are poor BVOC exchangers; (iii) soil is a significant BVOC source. [less ▲]

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See detailIRGA GAS SAMPLING SYSTEM DIMENSIONING: LABORATORY AND FIELD EXPERIMENTS
De Ligne, Anne ULg; Joly, Lilian; Cousin, Julien et al

Poster (2014, September 23)

The gas sampling system (GSS), which carries air from the sampling point to the IRGA, is an essential component of the eddy covariance system. It has to meet several constraints, among which minimizing ... [more ▼]

The gas sampling system (GSS), which carries air from the sampling point to the IRGA, is an essential component of the eddy covariance system. It has to meet several constraints, among which minimizing high frequency attenuation of concentration measurement and keeping pressure drop in the measurement cell in an acceptable range. Rain cup, filters, tubes and pumps are key elements of this system and need proper dimensioning. The elaboration of the ICOS protocol for IRGA required such dimensioning and optimization. Laboratory and field measurements were carried out with this aim. In the laboratory, a dynamic calibration bench was developed to investigate experimentally the pressure drop and the concentration fluctuation attenuation caused by different filters. In the field, three LI-7200 equipped with different GSS were installed and run at the Dorinne Terrestrial Observatory (ICOS-Belgium). Main experiment conclusions were that: • The shape and size of the rain cup has a critical impact on cut off frequencies • The filter porosity and size has a critical impact on pressure drop • Filter heating is necessary in order to avoid condensation and filter blocking These experiments led to the definition of the GSS functioning range that is finally proposed in the ICOS IRGA protocol. [less ▲]

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See detailAre agricultural ecosystems important BVOC « exchangers »? Evidences from 2 measurement years on croplands at Lonzée (Belgium)
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

Poster (2014, July 01)

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile ... [more ▼]

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile Organic Compounds) emission from terrestrial ecosystems. Indeed, those compounds which are mostly emitted by plants play a great role in the atmospheric chemistry, thereby influencing the Earth surface radiative budget and the tropospheric air quality. However, so far, very few is known about BVOC exchange by crops, implying that huge uncertainties remain about qualifying, quantifying and determining sources/sinks and driving mechanisms of BVOC exchanges between croplands ecosystems and the atmosphere. We present here the first long term BVOC fluxes measurement study conducted on maize (2012) and winter wheat (2013), respectively the second and first most important worldwide crops (FAOSTAT). BVOC exchange was measured using the disjunct by mass scanning eddy covariance technique (+ PTR-MS, Ionicon) at the Lonzée Terrestrial Observatory (ICOS site) in Belgium. Main results are: (i) crops emit mainly methanol; (ii) BVOC fluxes from studied crops is lower than in literature, suggesting that agricultural ecosystems are poor BVOC exchangers; (iii) soil is a significant BVOC source. [less ▲]

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See detailImpact of abiotic stresses on volatile organic compound production of field crops and grasslands
Digrado, Anthony ULg; Mozaffar, Ahsan ULg; Bachy, Aurélie ULg et al

Poster (2014, February 07)

Abiotic and biotic stresses are known to alter biogenic volatile organic compound (BVOC) emission from plants. With the climate and global change, BVOC emissions are likely to increase. This increase on ... [more ▼]

Abiotic and biotic stresses are known to alter biogenic volatile organic compound (BVOC) emission from plants. With the climate and global change, BVOC emissions are likely to increase. This increase on BVOC emissions could be driven by many environmental parameters like temperature, ozone and light availability for photosynthesis although it is still difficult to predict the impact of some environmental parameters, environmental controls on BVOC emission being species and BVOC-dependent. These BVOC are involved in a wide range of interactions of plants with their environment and these interactions could be affected by the global change. Moreover, BVOC also play a key role in the atmospheric chemistry and may contribute to ozone formation and an increase in methane lifetime, strengthening the global change. Yet, due to technical limitation, there are few studies examining the impact of multiple co-occurring stresses on BVOC emission at the ecosystem level although stress combination is probably more ecologically realistic in field. In the CROSTVOC (for CROp STress VOC) project, the impact of abiotic stresses (e.g. heat, drought, ozone and grazing) on BVOC emission will be investigated for field crops (maize and wheat) and grassland both at the ecosystem and plant scale. [less ▲]

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See detailImpact of grazing on carbon dioxide exchanges in an intensively managed Belgian grassland
Jerome, Elisabeth ULg; Beckers, Yves ULg; Bodson, Bernard ULg et al

in Agriculture, Ecosystems & Environment (2014), 194

Given that the soil carbon (C) sequestration potential by grasslands can be used to partly mitigate the total greenhouse gas emissions of livestock production systems, a better understanding of the ... [more ▼]

Given that the soil carbon (C) sequestration potential by grasslands can be used to partly mitigate the total greenhouse gas emissions of livestock production systems, a better understanding of the effects of management practices, and especially grazing, on grassland carbon dioxide (CO2) exchanges has become a major concern. This study aimed at quantifying grazing impact on CO2 fluxes measured by eddy covariance by using innovative data analyses and experiments. For that, we distinguished direct and indirect grazing impact. Indirect impact results from biomass consumption, excretion deposits and soil compaction by cattle that modify CO2 exchanges. Direct impact results from livestock CO2 emissions through respiration that add to total ecosystem respiration. For the indirect impact, the variation during periods with fixed stocking rate of gross primary productivity at light saturation (GPPmax) and normalized dark respiration (Rd,10) was analyzed. On average, GPPmax decreased during grazing periods and increased during non-grazing periods which could be explained by aboveground biomass reduction and re-growth, respectively. In addition, GPPmax variations were negatively correlated to grazing intensity (defined as the product of the stocking rate and the grazing duration). On the contrary, no significant evolution of Rd,10 was found during both grazing and non-grazing periods, probably due to a combination of opposing effects of grazing on the total ecosystem respiration components. The direct impact was emphasized through four specific designed confinement experiments. Each experiment extended over three successive days. On the first and third day, there was no cattle on the plot, while, on the second day, cattle were confined in the main wind direction area of the eddy covariance set-up to increase the stocking rate (≈26livestockunitsha-1). The average livestock CO2 emissions during confinement, FCO2,livestock, were deduced from the differences between half-hourly measurements taken at 24h interval with or without cattle and under similar environmental conditions. They were estimated to be 2.59±0.58kgClivestockunit-1d-1 on average. This result was corroborated by independent estimates based on the C ingested by cattle during confinement. Using an annual average stocking of 2livestockunitsha-1, we found that livestock CO2 emissions represent only 8% of this grassland annual total ecosystem respiration. To our knowledge, this study is the first to quantify both direct and indirect livestock contribution to CO2 fluxes exchanged at the ecosystem scale using the eddy covariance technique. © 2014 Elsevier B.V. [less ▲]

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See detailLong term observations of carbon dioxide exchange over cultivated savanna under a Sudanian climate in Benin (West Africa)
Ago, Expédit Evariste; Agbossou, Euloge Kossi; Galle, Sylvie et al

in Agricultural and Forest Meteorology (2014), 197

Turbulent CO2 exchanges between a cultivated Sudanian savanna and the atmosphere were measured during 29 months (August 2007–December 2009) by an eddy-covariance system in North-Western Benin, West Africa ... [more ▼]

Turbulent CO2 exchanges between a cultivated Sudanian savanna and the atmosphere were measured during 29 months (August 2007–December 2009) by an eddy-covariance system in North-Western Benin, West Africa. The site (Lat 9.74◦ N, Long 1.60◦ E, Alt: 449 m) is the one of three sites fitted out by the international AMMA-CATCH program. The flux station footprint area is mainly composed of herbs and crops with some sparse trees and shrubs. Fluxes data were completed by an inventory of dominating species around the tower and the meteorological measurements. Flux response to climatic and edaphic factors was studied. Water was found the main controlling factor of ecosystem dynamics: much larger uptake was found in wet than dry season. During wet season, a very clear answer of net CO2 fluxes to photosynthetic photon fluxes density (PPFD) was observed. A low limitation in response to saturation deficit and soil water variability was however observed. The total ecosystem respiration (TER) was found highly dependent on soil moisture below 0.1 m3m−3, but saturates above this threshold. The average annual carbon sequestration was 232 ± 27 gC m−2 with its inter-annual variability mainly controlled by TER. Finally, the ecosystem appeared more efficient during morning and wet season than during afternoon and dry period. [less ▲]

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See detailCharacterization of the soil CO2 production and its carbon isotope composition in forest soil layers using the flux-gradient approach
Goffin, Stéphanie; Aubinet, Marc ULg; Maier, Martin et al

in Agricultural and Forest Meteorology (2014), 188

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See detailA review on the use of entropy in landscape ecology: heterogeneity, unpredictability, scale dependence and their links with thermodynamics
Vranken, Isabelle ULg; Baudry, Jacques; Aubinet, Marc ULg et al

in Landscape Ecology (2014)

The identification of a universal law that can predict the spatiotemporal structure of any entity at any scale has long been pursued. Thermodynamics have targeted this goal, and the concept of entropy has ... [more ▼]

The identification of a universal law that can predict the spatiotemporal structure of any entity at any scale has long been pursued. Thermodynamics have targeted this goal, and the concept of entropy has been widely applied for various disciplines and purposes, including landscape ecology. Within this discipline, however, the uses of the entropy concept and its underlying assumptions are various and are seldom described explicitly. In addition, the link between this concept and thermodynamics is unclear. The aim of this paper is to review the various interpretations and applications of entropy in landscape ecology and to sort them into clearly defined categories. First, a retrospective study of the concept genesis from thermodynamics to landscape ecology was conducted. Then, 50 landscape ecology papers that use or discuss entropy were surveyed and classified by keywords, variables and metrics identified as related to entropy. In particular, the thermodynamic component of entropy in landscape ecology and its various interpretations related to landscape structure and dynamics were considered. From the survey results, three major definitions (i.e., spatial heterogeneity, the unpredictability of pattern dynamics and pattern scale dependence) associated with the entropy concept in landscape ecology were identified. The thermodynamic interpretations of these definitions are based on different theories. The thermodynamic interpretation of spatial heterogeneity is not considered relevant. The thermodynamic interpretation related to scale dependence is also questioned by complexity theory. Only unpredictability can be thermodynamically relevant if appropriate measurements are used to test it. [less ▲]

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See detailMEASUREMENT OF CATTLE METHANE EMISSIONS USING THE EDDY-COVARIANCE TECHNIQUE
Dumortier, Pierre ULg; Aubinet, Marc ULg; Debacq, Alain ULg et al

Poster (2014)

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions [1]. Recent technological advances in spectroscopy now permit methane flux ... [more ▼]

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions [1]. Recent technological advances in spectroscopy now permit methane flux measurement using eddy covariance. Methane fluxes exchanged by a pasture were measured continuously since June 2012 at the Dorinne Terrestrial Observatory in Belgium. During grazing periods, fluxes are dominated by enteric fermentation. Methane emissions were found strongly related to cattle stocking rate. When fluxes are integrated over large periods and assuming a random position of cows on the pasture, emission per LSU (Livestock Unit) was found to be 53±3 kg CH4 year-1 LSU-1. Recently, cattle position on the grassland was monitored continuously using GPS devices and combined with a footprint analysis [2] to derive more precisely the CH4 emission per LSU. A first experiment with a stocking rate close to 0.7 LSU ha-1 validated the approach and ended in a mean emission per head of 51±10 kg CH4 year-1 head-1. This approach also allows estimating emissions per head at the hourly scale and therefore opens the possibility of studying the circadian emission cycle and to link emissions to feeding behavior of the animal and feed quality. [less ▲]

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See detailYearly Follow-up of Methane Turbulent Exchange Over an Intensively Grazed Pasture in Belgium
Dumortier, Pierre ULg; Aubinet, Marc ULg; Beckers, Yves ULg et al

in Communications in Agricultural and Applied Biological Sciences (2014), 79(1), 91-96

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See detailEtablissement du bilan de carbone d’une exploitation agricole wallonne pratiquant le système allaitant : effets du climat et de la gestion du pâturage. Rapport de synthèse. Janvier 2012 – Décembre 2013.
Jerome, Elisabeth ULg; Dumortier, Pierre ULg; Beckers, Yves ULg et al

Report (2013)

Dans l’optique d’une atténuation des émissions de Gaz à Effet de Serre (GES) des systèmes d’élevage, les écosystèmes prairiaux peuvent jouer un rôle important vu leur potentiel de séquestration de carbone ... [more ▼]

Dans l’optique d’une atténuation des émissions de Gaz à Effet de Serre (GES) des systèmes d’élevage, les écosystèmes prairiaux peuvent jouer un rôle important vu leur potentiel de séquestration de carbone (C) dans les sols. Une évaluation pertinente de la contribution des systèmes d’élevage herbivores aux émissions de GES nécessite de raisonner en termes de bilan, en considérant à la fois les sources de GES et leur compensation via la séquestration de carbone par les prairies. Le projet « Etablissement du bilan de carbone d’une exploitation agricole wallonne pratiquant le système allaitant : effets du climat et de la gestion du pâturage » a pour objectif d’établir un inventaire de la contribution nette des systèmes d’élevage en Wallonie aux flux de GES (CO2, N2O, CH4). A long terme, nous étudierons les possibilités de réduction de ces émissions nettes par des adaptations des modes de conduite des systèmes d’élevage en adéquation avec leurs objectifs économiques et sociaux. L’exploitation étudiée est une exploitation agricole du type « naisseur-éleveur ». L’élevage se compose de vaches allaitantes et des veaux non sevrés de l’année de race « Blanc Bleu Belge culard ». Le système d’alimentation se base essentiellement sur la prairie permanente durant la période estivale et les produits conservés de la prairie durant la période hivernale. Ce rapport constitue l’état d’avancement du projet au terme de la deuxième biennale. [less ▲]

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See detailFifty years of crop residue management have a limited impact on soil heterotrophic respiration.
Buysse, Pauline ULg; Schnepf-Kiss, Anne-Caroline; Carnol, Monique ULg et al

in Agricultural and Forest Meteorology (2013), 180

The impacts of crop residue management on soil microbial biomass, labile carbon and heterotrophic respiration (HR) were assessed at a long-term experimental site in the Hesbaye region in Belgium. Three ... [more ▼]

The impacts of crop residue management on soil microbial biomass, labile carbon and heterotrophic respiration (HR) were assessed at a long-term experimental site in the Hesbaye region in Belgium. Three treatments, residue export (RE), farmyard manure addition (FYM) and residue restitution after harvest (RR), have been applied continuously since 1959. The soil is a Eutric Cambisol with, in 2010, significantly different total soil organic carbon contents of 4.4, 5.1 and 5.9 kg C m-2 under the RE, RR and FYM treatments, respectively. Manual field HR measurements were carried out during the 2010 and 2012 crop seasons using a dynamic closed chamber system. Microbial biomass, labile C content and metabolic diversity of soil bacteria were assessed in spring 2012. Fifty-one years after the beginning of the treatments, residue management had a limited impact on HR. Based on daily averaged values, the treatment had a significant impact (α = 10%) in 2012 but not in 2010. Based on the individual measurement dates, the treatment impact was less obvious in 2012; with the observation of a significant impact (α = 10%) on HR in only 7% and 36.8% of the measurement dates in 2010 and 2012, respectively. Labile C and microbial biomass were significantly lower in the RE treatment than in FYM and RR. Residue management had no significant effect on cold-water extracted carbon and metabolic diversity of heterotrophic soil bacteria. The limited impact of residue management on HR could be explained by (i) the relatively low amounts of recent above-ground crop inputs, (ii) the large proportion of below-ground residues and other non-exportable above-ground residues reducing the potential differences between treatments and (iii) the relatively large spatial variability of HR. In conclusion, carbon losses due to heterotrophic respiration did not differ between RE, FYM and RR treatments in the studied soil. This contrasts with the different soil organic carbon contents observed in these three treatments after fifty years of experiment. Further investigations regarding the reduction of spatial variability and the potential roles played by organic matter protection within aggregates and biochemical composition of inputs are needed. [less ▲]

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