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See detailUpscaling winter wheat above-ground biomass measurements using multispectral imagery and 3D data from unmanned aerial vehicle
Michez, Adrien ULiege; Bauwens, Sébastien ULiege; Heinesch, Bernard ULiege et al

Poster (2017, October 20)

Field measurements in the ICOS program are spatially limited whereas the monitored gas fluxes may have a large footprint. Aerial remote sensing has the advantage to monitor large areas. The main goal of ... [more ▼]

Field measurements in the ICOS program are spatially limited whereas the monitored gas fluxes may have a large footprint. Aerial remote sensing has the advantage to monitor large areas. The main goal of our research was to test the potential of unmanned aerial vehicles (UAV) to upscale parameters monitored through the ICOS program. In this study, we specifically focus on above-ground biomass (AGB) monitoring in a winter wheat crop. We used a octocopter drone (X frame type) to acquire a time series over the crop growing season (8 flights from the 14th of February 2017 to the 7th of July 2017) of multispectral imagery covering the ICOS candidate station of Lonzée (Wallonia, Belgium) and the surrounding field crop areas (ca. 0.25 km² per flight). The multispectral camera provides spectral information on the green (550 +/- 50 nm), red (660 +/- 50 nm), near infrared (735 +/- 50 nm) and red-edge (790 +/- 10 nm) wavelengths bands. The UAV also brought an off-the-shelf high resolution (20 Mpx) RGB camera to derive accurate 3D data. We performed a photogrammetric 3D reconstruction of the acquired imagery for every flight survey. The images provided by the RGB sensor (Sony RX100) were used to produce a high spatial resolution Digital Surface Model (0.05 m) and the images acquired by the multispectral sensor were used to derive reflectance maps (0.1 m) in the four wavelengths bands. The four reflectance layers were combined to produce two straight-forward vegetation indices (Normalized Difference Vegetation Index and Green NDVI). The photogrammetric DSM’s were combined to a LiDAR Digital Terrain Model (public database, survey in winter 2013) to produce Crop Height Models (CHM) of the study area. We used multiple linear regressions modelling in order to predict the AGB of the field crop monitored by the ICOS station of Lonzée with UAV imagery. AGB=a+b*GNDVI+c*NDVI+d *CHM The field crop data were provided by the ICOS program and by field research conducted in experimental field crops close to the flux tower. The field sampling consisted in destructive samples of the crop which were weighted after drying. For each field sample, an associated area was computed based on the outdistance sowing and the number of sampled crops in order to compute an AGB per area unit (t / Ha). Each AGB field estimation was associated to the closest flight date to build a multi date model presenting good performances (r² = 0.85, RMSE = 2.3 t/Ha). We used the same modelling approach to adjust a single date model to derive a predicted AGB map for the 7th of July. The performance of the single date model is lower but still highlights the biomass variation within the crop (r² = 0.71, RMSE = 1.9 t/Ha). The predicted AGB map displays a high spatial heterogeneity with some spatial patterns. Locally low AGB values are found along two old pedestrian whereas higher AGB values can be associated to areas which were sprayed twice (in-between two tractor tracks). Our results highlight the potential of UAV multispectral imagery to monitor the AGB variation within the footprint of the flux tower and highlight the need for repeated field sampling with a precise geolocation to improve the matching between the flight and the field surveys. [less ▲]

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See detailInfluences of feeding behaviour and forage quality on diurnal methane emission dynamics of grazing cows
Blaise, Yannick ULiege; Andriamandroso, Andriamasinoro ULiege; Heinesch, Bernard ULiege et al

in Berckmans, Daniel; Keita, Keita (Eds.) Precision Livestock Farming ‘17 (2017, September 12)

This study aimed to evaluate diurnal methane (CH4) emission dynamics of grazing cattle and highlight their relationships with biotic factors such as the feeding behaviour as well as seasonal changes in ... [more ▼]

This study aimed to evaluate diurnal methane (CH4) emission dynamics of grazing cattle and highlight their relationships with biotic factors such as the feeding behaviour as well as seasonal changes in pasture characteristics. Existing methods to assess grazing ruminants’ daily CH4 emissions provide useful insights to investigate mitigation strategies relying on feeding and genetic selection. Nonetheless such methods based on tracer gases (SF6) or feeding bins equipped with sniffers (e.g. GreenFeed) can hardly cover diurnal CH4 emission fluctuations which can influence the accuracy of total CH4 production estimations. Previous studies in barns showed that emission dynamics strongly vary during post feeding time, leading to a possible bias in estimates of daily CH4 emissions as high as 100%. To investigate whether such fluctuations are also taking place on pasture, a portable device was designed with infrared CH4 and CO2 sensors measuring concentrations in the exhaled air at a high sampling rate (4 Hz). Six grazing dry red-pied cows were equipped with the device and motion sensors during runs of 24h to monitor CH4 and CO2 emissions and detect their feeding behaviours (grazing, rumination and other behaviours), respectively. This experiment was performed in summer and fall in order to cover seasonal changes in pasture forage quality. Methane emission was estimated from the CH4:CO2 concentration ratio and the metabolic CO2 production of the cows. As for barn studies, variations were observed in total daily CH4 emission due to the seasons and diurnal variations were also observed due to animal behaviours. Relationships between animal feeding behaviour and CH4 emissions patterns on pasture were also unravelled. [less ▲]

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See detailImpact of canopy aerodynamic distance spatial and temporal variability on long term eddy covariance measurements
Hurdebise, Quentin ULiege; Heinesch, Bernard ULiege; De Ligne, Anne ULiege et al

in Agricultural and Forest Meteorology (2017), 247(2017), 131-138

Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements. It requires characterizing the ... [more ▼]

Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements. It requires characterizing the surrounding environment. One way to achieve this is to analyse the canopy aerodynamic distance (Δ), which is the difference between measurement height (zm) and displacement height (d). In this work, an original method to estimate the canopy aerodynamic distance at a fine spatial (30° sectors) and temporal (one year) resolution was proposed. It was based on sensible heat cospectra analysis, calibrated on a measurement height change and validated using canopy height inventories. This method was applied to 20 years of eddy covariance measurements from the Vielsalm Terrestrial Observatory (VTO), a site located in a mixed temperate forest. The method allowed Δ spatio-temporal variability due to changes in canopy or measurement height to be detected. Relationships between Δ and turbulence statistics were then analysed: the momentum correlation coefficient (ruw) was found to be dependent on Δ, confirming that the measurements were made in the roughness sublayer of the atmospheric surface layer. In contrast, no such relationship was found sensible heat, CO2 or water vapour correlation coefficients, suggesting that the Δ variability did not affect significantly these fluxes. There were significant differences, however, between azimuthal directions, suggesting that these scalars were affected by forest heterogeneity in a different way. Various hypotheses were put forward to explain the differences and their relevance was evaluated. This study highlighted the need to consider the spatial and temporal variability of the surrounding environment in order to verify the consistency of long-term eddy covariance datasets. [less ▲]

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See detailAntarctic sea ice trophic status
Van der Linden, Fanny ULiege; Moreau, Sébastien; Champenois, Willy ULiege et al

Poster (2017, July)

The sea ice ecosystem is characterized by steep gradients in temperature, salinity, light and nutrient availability. Despite these challenging environmental conditions, sea ice provides a dynamic habitat ... [more ▼]

The sea ice ecosystem is characterized by steep gradients in temperature, salinity, light and nutrient availability. Despite these challenging environmental conditions, sea ice provides a dynamic habitat for diverse communities of microorganisms. These communities include a wide variety of organisms from different taxonomic groups such as algae, bacteria, heterotrophic protists, fungi as well as viruses [Horner et al., 1992; Deming, 2010; Thomas and Dieckmann, 2010; Poulin et al., 2011]. In the frame of the YROSIAE project (Year-Round survey of Ocean-Sea-Ice-Atmosphere Exchanges), carried out at Cape Evans in McMurdo Sound (Antarctica) from Nov. 2011 to Dec. 2012, ice cores, seawater, and brine material were collected at regular time intervals. Physical properties (salinity, temperature, texture) and biogeochemical parameters (pCO2, dissolved inorganic carbon, total alkalinity, chlorophyll-a, macro-nutrients) were analysed. We will here particularly consider changes inused dissolved inorganic carbon (DIC) and chlorophyll-a (chl-a) , used as a proxiesy of net community production and autotrophic biomass, respectively. A high spatial and temporal variability in ice algal biomass and DIC evolution were observed. From spring, very high chl-a concentrations (>2400μg.L^(-1)) were observed at the bottom of the ice, a common feature of land fast ice in the McMurdo Sound. This suggests high primary production. However Strikingly, , at the same time, nutrients at the bottom of the ice increased significantly suggesting high heterotrophyremineralisation. In the middle of the ice column, evolution of DIC is was marked by a succession of autotrophic and heterotrophic phases. The overall increase of DIC suggests that the ice interior was rather heterotroph. Such sea ice system should expel CO2. Yet, strong under-saturation in CO2 and DIC depletion appeared at the ice surface, suggesting that sea ice was taking up CO2 from the atmosphere. On the whole, land fast sea ice in McMurdo Sound appears as a puzzling ecosystem. It is able to support elevated growth of autotrophic organisms at the bottom, but still appears to be heterotrophicin parallel to high remineralization, while the top of the ice appears to be rather heterotrophic but stilland able to pump CO2 from the atmosphere. [less ▲]

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See detailEnvironmental controls of biogenic volatile organic compound emissions from a grazed grassland in Dorinne, Belgium
Michel, Colin ULiege; Heinesch, Bernard ULiege; Bachy, Aurélie ULiege et al

Poster (2017, June 15)

Despite the growing interest for oxygenated volatile organic compounds (OVOC) over the last 15 years due to their role in the atmospheric chemistry, current knowledge about OVOC exchanges by grassland and ... [more ▼]

Despite the growing interest for oxygenated volatile organic compounds (OVOC) over the last 15 years due to their role in the atmospheric chemistry, current knowledge about OVOC exchanges by grassland and the environmental factors driving them still entails gaps. However, those ecosystems represent an important part of the total earth surface (13.37%). This study conducted on a grazed grassland therefore aims to quantify OVOC exchanges over full grazing seasons in order to understand the mechanisms behind these OVOC exchanges. The Eddy Covariance method was used for flux quantification, with a PTR-MS for the measurements of OVOCs mixing ratios. It took place within the activities of the CROSTVOC project (CROp Stress VOC) and therefore gives an important attention to the stress induced fluxes. BVOC flux measurements were also performed on a smaller scale by using all-teflon automated dynamic chambers covering a surface of 0.1 m² each. [less ▲]

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See detailDevelopment of an open-source algorithm based on inertial measurement units (IMU) of a smartphone to detect cattle grass intake and ruminating behaviors
Andriamandroso, Andriamasinoro ULiege; Lebeau, Frédéric ULiege; Beckers, Yves ULiege et al

in Computers & Electronics in Agriculture (2017), 139

In this paper, an open algorithm was developed for the detection of cattle’s grass intake and rumination activities. This was done using the widely available inertial measurement unit (IMU) from a ... [more ▼]

In this paper, an open algorithm was developed for the detection of cattle’s grass intake and rumination activities. This was done using the widely available inertial measurement unit (IMU) from a smartphone, which contains an accelerometer, a gyroscope, a magnetometer and location sensors signals sampled at 100 Hz. This equipment was mounted on 19 grazing cows of different breeds and daily video sequences were recorded on pasture of different forage allowances. After visually analyzing the cows’ movements on a calibration database, signal combinations were selected and thresholds were determined based on 1-s time windows, since increasing the time window did not increase the accuracy of detection. The final algorithm uses the average value and standard deviation of two signals in a two-step discrimination tree: the gravitational acceleration on x-axis (Gx) expressing the cows’ head movements and the rotation rate on the same x-axis (Rx) expressing jaw movements. Threshold values encompassing 95% of the normalized calibrated data gave the best results. Validation on an independent database resulted in an average detection accuracy of 92% with a better detection for rumination (95%) than for grass intake (91%). The detection algorithm also allows for characterization of the diurnal feeding activities of cattle at pasture. Any user can make further improvements, for data collected at the same way as the iPhone’s IMU has done, since the algorithm codes are open and provided as supplementary data. [less ▲]

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See detailUsing crop modelling to determine the meteorological conditions to be implemented in an Ecotron facility - Prerequisites to improve the experimental design?
Dumont, Benjamin ULiege; Leemans, Vincent ULiege; Garré, Sarah ULiege et al

Poster (2017, May 23)

An Ecotron is a facility where ecosystems are confined in experimental chambers, allowing the simultaneous control of environmental conditions and the on-line monitoring of processes. Under the threats of ... [more ▼]

An Ecotron is a facility where ecosystems are confined in experimental chambers, allowing the simultaneous control of environmental conditions and the on-line monitoring of processes. Under the threats of climate change and the pressure of a world growing population, such facilities will be of major importance to study the relations between climate change and agro-ecosystems.As it can quickly become time- and money-consuming, conducting experiments in an Ecotron will force researchers to cautiously select the climate of interest to be generated. They will thus need reliable tools to help them support the decision making process.Here, we present an innovative methodology, supported by the use of crop model, to assist researchers in finding the climatic conditions under which crop services will be impacted.The meteorological datasets among which the choice can be done were generated by the ALARO-0 model (RMI, Belgium) for current and future climatic conditions. Runs were conducted for the historical period 1981-2010, and for two time frames - 2041-70 and 2071-2100 - under two emissions scenarios - RCP 4.5 and 8.5.A crop model (STICS, INRA, FR) was run over the entire database. Crop model outputs were synthesized for the main crop phenological phases, i.e. the juvenile, vegetative and reproductive phases. A particular emphasis was put on agronomical outputs (biomass and grain yield) and crop growth stresses (deficit and excess of water, thermal and nutrient stresses).Using these outputs as selection criteria, a novel multi-criteria approach was designed to retro-select the specific climatic conditions allowing to reach certain outcomes (e.g. yield target) while simultaneously exhibiting given thresholds of stresses for any considered crop stages. [less ▲]

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See detailGrazing-induced BVOC fluxes from a managed grassland
Mozaffar, Ahsan ULiege; Schoon, N.; Bachy, Aurélie ULiege et al

Poster (2017, April 28)

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See detailN2O eddy covariance fluxes : from field measurements to flux analysis
Lognoul, Margaux ULiege; Debacq, Alain ULiege; Heinesch, Bernard ULiege et al

Poster (2017, April 28)

N2O eddy covariance data were collected for a complete season of sugar beet crop (from first fertilization to harvest). Data treatment and preliminary results are presented.

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See detailReduced Tillage generates higher N2O emissions: results of continuous chamber-based measurement in a winter wheat field.
Broux, François ULiege; Lognoul, Margaux ULiege; Theodorakopoulos, Nicolas et al

Poster (2017, April 24)

Agriculture is one of the most important contributors to GHG emission, notably through fertilized croplands. Though, few publications have studied simultaneously and through continuous measurement the N2O ... [more ▼]

Agriculture is one of the most important contributors to GHG emission, notably through fertilized croplands. Though, few publications have studied simultaneously and through continuous measurement the N2O and CO2 emissions in cultivated lands. We conducted this study to assess the effect of farming practices and climate on both N2O and CO2 emissions from a winter wheat crop. The experiment was held in an experimental field in the loamy region in Belgium from March 2016 till crop harvest in August 2016. The fluxes were measured on two nearby parcels in a winter wheat field with restitution of the residues from previous crop. For the past 8 years, one parcel was subjected to a Reduced tillage (RT, 10 cm depth) and the other one to a conventional tillage (CT, 25 cm depth). On each parcel, the emissions are assessed with homemade automated closed chambers. Measurement continuity and good temporal resolution (one mean flux every 4 hours) of the system allowed a fine detection and quantification of the emission peaks which usually represent the major part of N2O fluxes. In addition to gas fluxes, soil water content and temperature were measured continuously. Soil samples were taken regularly to determine soil pH, soil organic carbon and nitrogen pools (total, NO3- and NH4+) and study microbial diversity and nitrification/denitrification gene expression. Surprisingly, results showed N2O emissions twice as large in the RT parcel as in the CT parcel. On the contrary, less important CO2 emissions were observed under RT. Several emission peaks of N2O were observed during the measurement period. The peaks occurred after fertilization events and seemed to be triggered by an elevation of soil water content. Interesting links could be made between soil NH4-N and NO3-N pools and N2O emissions. Nitrification being the main process originating the fluxes was suggested on the one hand by the temporal evolution of nitrogen pools and N2O emissions and on the other hand by the relation between spatial variability of the emissions with the soil nitrate content. A comparison of the emissions between ST and CT and a discussion on peaks temporal dynamic, focusing on their intensity, duration and starting time will be presented. [less ▲]

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See detailMomentum, sensible heat and CO2 correlation coefficient: what can we learn from 20 years of eddy covariance measurements
Hurdebise, Quentin ULiege; De Ligne, Anne ULiege; Vincke, Caroline et al

Poster (2017, April 24)

Long-term data series of carbon dioxide and other gas exchanges between terrestrial ecosystems and atmosphere become more and more numerous. Long-term analyses of such exchanges require a good ... [more ▼]

Long-term data series of carbon dioxide and other gas exchanges between terrestrial ecosystems and atmosphere become more and more numerous. Long-term analyses of such exchanges require a good understanding of measurement conditions during the investigated period. Independently of climate drivers, measurements may indeed be influenced by measurement conditions themselves subjected to long-term variability due to vegetation growth or set-up changes. The present research refers to the Vielsalm Terrestrial Observatory (VTO) an ICOS candidate site located in a mixed forest (beech, silver fir, Douglas fir, Norway spruce) in the Belgian Ardenne. Fluxes of momentum, carbon dioxide and sensible heat have been continuously measured there by eddy covariance for more than 20 years. During this period, changes in canopy height and measurement height occurred. The correlation coefficients (for momemtum, sensible heat and CO2) and the normalized standard deviations measured for the past 20 years at the Vielsalm Terrestrial Observatory (VTO) were analysed in order to define how the fluxes, independently of climate conditions, were affected by the surrounding environment evolution, including tree growth, forest thinning and tower height change. A relationship between canopy aerodynamic distance and the momentum correlation coefficient was found which is characteristic of the roughness sublayer, and suggests that momentum transport processes were affected by z-d. In contrast, no relationship was found for sensible heat and CO2 correlation coefficients, suggesting that the z-d variability observed did not affect their turbulent transport. There were strong differences in these coefficients, however, between two wind sectors, characterized by contrasted stands (height differences, homogeneity) and different hypotheses were raised to explain it. This study highlighted the importance of taking the surrounding environment variability into account in order to ensure the spatio-temporal consistency of datasets. [less ▲]

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See detailCanopy aerodynamic distance (z-d) estimation and impact on eddy covariance measurements
Hurdebise, Quentin ULiege; De Ligne, Anne ULiege; Vincke, Caroline et al

in Geophysical Research Abstracts 2017 (2017, April 24)

Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements above growing and heterogeneous ... [more ▼]

Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements above growing and heterogeneous ecosystems. It requires characterizing the surrounding environment. One way to achieve this is to analyse the canopy aerodynamic distance, which is the difference between measurement height (z) and displacement height (d). In this study, twenty years of eddy covariance measurements from the Vielsalm Terrestrial Observatory, a site located in a mixed temperate forest, were used. Canopy aerodynamic distance (z-d) estimates were obtained using two micrometeorological methods: the first one, which is original so far as we know, was based on analysing sensible heat cospectra; the second one was derived from the wind speed profile equation. Canopy height estimates based on inventories were used to validate both methods. The micrometeorological methods allowed the z-d variations due to changes in canopy or measurement height to be detected. In addition, the results obtained using the two methods were well correlated, spatially and temporally, with the z-d derived from canopy height measurements. The micrometeorological approaches used could therefore be a promising tool for investigating z-d variability at a high directional and temporal resolution. Questions remain, however, particularly with regard to the variability observed that cannot be explained by canopy or measurement height variation. Forest management practices and the non-fulfilment of similarity relationships were suspected to be the main explanatory factors. [less ▲]

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See detailImpact of tillage on greenhouse gas emissions by an agricultural crop and dynamics of N2O fluxes: Insights from automated closed chamber measurements
Lognoul, Margaux ULiege; Theodorakopoulos, Nicolas ULiege; Hiel, Marie-Pierre ULiege et al

in Soil & Tillage Research (2017), 167

Our experiment aimed at studying the impact of long term tillage treatments – reduced tillage (RT) and conventional tillage (CT), on CO2 and N2O emissions by soil and at describing the dynamics of N2O ... [more ▼]

Our experiment aimed at studying the impact of long term tillage treatments – reduced tillage (RT) and conventional tillage (CT), on CO2 and N2O emissions by soil and at describing the dynamics of N2O fluxes. Gas measurements were performed from June to October 2015 in a Belgian maize crop, with homemade automated closed chambers, allowing continuous measurement at a high temporal resolution. After 7 years of treatment, CO2 and N2O average emissions were significantly larger in the RT parcel than in the CT parcel. This observation was attributed to the effect of tillage on the distribution of crop residues within the soil profile, leading to higher soil organic C and total N contents and a greater microbial biomass in the upper layer in RT. A single N2O emission peak triggered by a sudden increase of water- filled pore space (WFPS) was observed in the beginning of the measuring campaign. The absence of large emission afterwards was most likely due to a decreasing availability of N as crop grew. N2O background fluxes showed to be significantly correlated to CO2 fluxes but not to WFPS, while the influence of soil temperature remained unclear. Our results question the suitability of reduced tillage as a “climate-smart” practice and suggest that more experiments be conducted on conservation practices and their potent negative effect on environment. [less ▲]

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See detailMethane balance of an intensively grazed pasture and estimation of the enteric methane emissions from cattle
Dumortier, Pierre ULiege; Aubinet, Marc ULiege; Beckers, Yves ULiege et al

in Agricultural and Forest Meteorology (2017), 232

The methane turbulent fluxes of an intensively grazed pasture were measured continuously from June 2012 to December 2013 at the Dorinne Terrestrial Observatory (DTO) in Belgium. During grazing periods ... [more ▼]

The methane turbulent fluxes of an intensively grazed pasture were measured continuously from June 2012 to December 2013 at the Dorinne Terrestrial Observatory (DTO) in Belgium. During grazing periods, the fluxes were dominated by enteric fermentation and were found to be strongly related to cow stocking density. In 2013, total emission from the pasture was found between 9 and 11 g CH4 m−2, 97% of which being emitted during grazing periods. Emission per LU (livestock unit) was estimated in a non-invasive way by integrating eddy covariance fluxes over large periods and by assuming a homogeneous average cattle disposition on the pasture. This estimate was compared to the one obtained during confinement periods, where cows were confined in a small part of the pasture. The emission per LU varied between 104 and 134 g CH4 LU−1 day−1 (13 and 17 g CH4 kg DMI−1), depending on the dataset and the computation method used. Diel course was characterized by two emission peaks, one in the morning and a larger one in the afternoon. For rest periods (no cattle on the pasture), small emissions were observed (median and mean values of 0.5 and 1.5 mg CH4 m−2 day−1, respectively). [less ▲]

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See detailCarbon budget measurement over 12 years at a crop production site in the silty-loam region in Belgium
Buysse, Pauline; Bodson, Bernard ULiege; Debacq, Alain ULiege et al

in Agricultural and Forest Meteorology (2017), 246

Carbon dioxide (CO2) exchanges between crops and the atmosphere are influenced by both climatic and management drivers. In this study, a site at the Lonzée Terrestrial Observatory (candidate ICOS site) in ... [more ▼]

Carbon dioxide (CO2) exchanges between crops and the atmosphere are influenced by both climatic and management drivers. In this study, a site at the Lonzée Terrestrial Observatory (candidate ICOS site) in Belgium that had been managed for more than 70 years using conventional farming practices, was monitored over three complete rotation cycles (sugar beet/winter wheat/seed potato/winter wheat) from 2004 to 2016. Continuous eddy-covariance measurements and regular biomass samplings were performed in order to obtain the daily and seasonal Net Ecosystem Exchange (NEE), Gross Primary Productivity (GPP), Total Ecosystem Respiration (TER), Net Primary Productivity (NPP) and Net Biome Production (NBP). Meteorological data and crop management practices were also recorded. Over the 12 crop seasons, total NEE varied both between and within crop types. Crop type influenced net carbon (C) sequestration, with the seed potato crop exhibiting the smallest C fluxes. Despite differences in CO2 assimilation response to weather variables and in cumulated TER/GPP dynamics, the sugar beet, winter wheat and maize crops had similar seasonal NEE values. The NEE inter-annual variability, both between and within crop types, was explained mainly by the length of the active vegetation period, as well as the cumulated photosynthetic photon flux density and average air temperature during this period. The establishment of the C budget over the 12 years of study showed that NEE was a downward (negative) flux (−4.40 ± 0.05 kg C m−2), but NBP was an upward (positive) flux (0.99 ± 0.22 kg C m−2). That is, as soon as C exportation at harvest and C importation (manure, slimes) were included in the budget, the site behaved as a C source. The intercrop periods contributed significantly to the total C budget, and the C fluxes generated during these periods were positively related to crop residue amount and temperature. The largest uncertainties about the crop C budget were those relating to biomass measurements. Carrying out a soil C inventory would help to validate the NBP-based estimate of soil C loss. [less ▲]

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See detailMethanol emissions from maize: Ontogenetic dependence to varying light conditions and guttation as an additional factor constraining the flux
Mozaffar, Ahsan ULiege; Schoon, N.; Digrado, Anthony ULiege et al

in Atmospheric Environment (2017), 152

Because of its high abundance and long lifetime compared to other volatile organic compounds in the atmosphere, methanol (CH3OH) plays an important role in atmospheric chemistry. Even though agricultural ... [more ▼]

Because of its high abundance and long lifetime compared to other volatile organic compounds in the atmosphere, methanol (CH3OH) plays an important role in atmospheric chemistry. Even though agricultural crops are believed to be a large source of methanol, emission inventories from those crop ecosystems are still scarce and little information is available concerning the driving mechanisms for methanol production and emission at different developmental stages of the plants/leaves. This study focuses on methanol emissions from Zea mays L. (maize), which is vastly cultivated throughout the world. Flux measurements have been performed on young plants, almost fully grown leaves and fully grown leaves, enclosed in dynamic flow-through enclosures in a temperature and light-controlled environmental chamber. Strong differences in the response of methanol emissions to variations in PPFD (Photosynthetic Photon Flux Density) were noticed between the young plants, almost fully grown and fully grown leaves. Moreover, young maize plants showed strong emission peaks following light/dark transitions, for which guttation can be put forward as a hypothetical pathway. Young plants’ average daily methanol fluxes exceeded by a factor of 17 those of almost fully grown and fully grown leaves when expressed per leaf area. Absolute flux values were found to be smaller than those reported in the literature, but in fair agreement with recent ecosystem scale flux measurements above a maize field of the same variety as used in this study. [less ▲]

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See detailIncreased expression of bacterial amoA during an N2O emission peak in an agricultural field
Theodorakopoulos, Nicolas ULiege; Lognoul, Margaux ULiege; Degrune, Florine ULiege et al

in Agriculture, Ecosystems & Environment (2017), 236

Levels of N-cycle gene transcripts (nirK, nirS, nosZ, amoA) were measured during an N2O emission peak in an agricultural soil. Automated dynamic closed chambers were used to monitor an N2O emission peak ... [more ▼]

Levels of N-cycle gene transcripts (nirK, nirS, nosZ, amoA) were measured during an N2O emission peak in an agricultural soil. Automated dynamic closed chambers were used to monitor an N2O emission peak on a maize crop after a natural rainfall. The peak occurred rapidly after the rainfall began. Spatial and temporal variability in N2O emission was observed between chambers. An analysis of N-cycle gene transcript levels revealed an increase in bacterial amoA gene transcripts (but not in archaeal amoA transcripts), correlating strongly with N2O emission. This suggests the involvement of nitrification enzymes, despite a high water-filled pore space (80%). Reverse transcription of bacterial 16S rRNA followed by partial sequencing of the resulting cDNAs revealed few rainfall-induced changes in the potentially active bacterial community, and notably no significant change in the relative abundance of 16S rRNAs from the nitrifier genus Nitrosospira. Expression of the amoA gene appears as a possible proxy for monitoring the N2O emission peak. To our knowledge, this is the first experiment to evaluate the expression of N-cycle genes during an N2O emission peak on an agricultural field. [less ▲]

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