Seasonal variation of LAI in the footprint of a flux measurement tower

C

Modélisation de la réponse des flux de respiration d'un sol forestier selon les principales variables climatiques

Modelling of the response of forest soil respiration fluxes to the main climatic variables. The objective of this article is to model the carbon dioxide (CO2) efflux to the atmosphere due to soil respiration. First, we will synthesize the main components of soil respiration fluxes as found in the literature. Then, we will present a system of automatic measurements, which was set up in a forest stand in Vielsalm (Ardennes, Belgium). This system recorded measurements of soil efflux and of climatic variables every 30 minutes. Its spatial resolution was limited to six collars of 20 cm diameter in a two-meter diameter curve. The measurements were analyzed according to their climatic components: temperature and relative soil water content. We analyzed 2 2 , 9 2 6 cycles of soil respiration measurements, and we followed a strict procedure of data selection in order to characterize soil respiration fluxes according to the main environmental components. We modelized those soil temperature-dependent fluxes with a Q1 0 function and A r r h e n i u s ' law with temperature-adjusted activation energ y, which both gave very similar results. Our best estimation for Q1 0 is 3.86 and for A in Arrhenius ' l a w, 17,479. We then adjusted two line segments beneath and beyond 0 . 2 7 m3.m- 3 of water in the soil in order to describe the response of respiration fluxes to soil moisture content. The soil temperature at 4.5 cm could explain over 86 % of the soil respiration fluxes. Relative moisture content narrows this by 2 %

Chamber-based continuous measurement of N2O fluxes in a winter wheat field: comparison of tillage treatments and identification of emission peak dynamic

Agriculture is the first anthropogenic source of N2O, notably through fertilized croplands. Though, few publications have studied through continuous measurement the N2O emissions in cultivated lands. We conducted this study to assess the effect of farming practices and climate on N2O 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 N2O fluxes are 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 N2O emissions were 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 at various depths and surface 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. Measurements are still in progress. First results suggested that fluxes were about 3 times larger in the RT parcel than in the CT parcel. Several emissions peaks were observed during the measurement period. The peaks occurred after fertilization events and seemed to be triggered by an elevation of soil water content. A comparison of the emissions between RT and CT and a discussion on peak temporal dynamics, focusing on their intensity, duration and starting time will be presented.AgriGE

ANALYSES DE PROPRIÉTÉS HYDROPHYSIQUES D’UN SOL AGRICOLE SOUMIS À DIFFÉRENTS TRAITEMENTS CULTURAUX DANS LE CADRE DU PROJET SOLRESIDUS

Le projet SOLRESIDUS est une collaboration entre diverses unités au sein de GxABT. Il vise à analyser l’impact du mode de travail du sol (labour/non labour, restitution/exportation des pailles) sur divers paramètres édaphiques/culturaux d’un champ de blé d’hiver (parcelles du Bordia). Le but du projet est de fournir une approche multidisciplinaire à l’analyse de systèmes agricoles. Afin de favoriser l’interaction entre les différentes unités, une base de données regroupant les différents résultats et méthodologies sera créée. Plus spécifiquement, les mesures touchant aux systèmes Eau-Sol (Unités d’Hydrologie et de Physique) incluent des courbes de rétention (pF), des évaluations d’infiltrabilité (tensio-infiltromètres, anneaux), des profils d’humidité (manuels et automatiques) et une caractérisation de la macro et microstructure porale (scan 3D par tomographie à rayons X). Ces mesures seront faites tout au long du projet (2 ans), afin d’établir une base solide à la compréhension du comportement hydrophysique d’un sol agricole limoneux. Ceci inclut un suivi des paramètres lors de l’évolution de la culture, mais également une comparaison entre les modalités

Carbon budget of a sugar beet crop

Peer reviewe

Stockage de carbone et flux de gaz à effet de serre en prairie (synthèse bibliographique)

Carbon sequestration and greenhouse gas fluxes in grassland. A review. Grassland carbon (C) sequestration can play an important role in mitigating total greenhouse gas (GHG) emissions of livestock production systems. An accurate inventory of livestock production system contribution to GHG emissions requires to think in terms of global budget, by considering both the GHG sources and the mitigation potential trough grassland soil carbon sequestration. There is a huge variability in C and GHG balances of grasslands that is mainly due to management practices and climatic conditions. The present article shows that, to reduce the uncertainties of the results, long term measurements at the field scale are necessary. Also, it shows the importance of taking into account the fluxes of the three main GHGs (carbon dioxide, nitrous oxide, methane) into account when calculating the GHG budget. This article also highlights the need for a better understanding of the mechanisms driving the fluxes, in relation to environmental factors and management practices, in order to propose mitigation strategies able to enhance soil carbon sequestration in soils and to reduce methane and nitrous oxide emissions

Interannual variability of CO2 fluxes, growth and yield by a winter wheat crop (Triticum aestivum L.)

In this study, two winter wheat (Triticum aestivum L.) cropping seasons were compared at the Lonzée (Belgium) experimental site. The site, crop management, sowing and harvest dates were similar on the two years. The main difference between the seasons was due to to climate conditions. Continuous eddy-covariance fluxes, leaf scale photosynthesis measurements and crop development monitoring were performed during the whole vegetation periods. Globally, the two years were characterised by a higher than normal air temperature (9.9 °C and 11.9 °C respectively against 9.4 °C for standard) and lower than normal rainfalls (595.1 mm and 675.1 mm respectively against 772 mm for standard). In addition, the second season (2006-2007) was characterised by an exceptionally mild winter, dry and hot conditions in April and by humid and cloudy conditions during the last vegetation phases. These particular conditions induced earlier growth stages and the comparison of global fluxes gives contrasting results: gross primary productivity (GPP) was larger in 2007 but, on the contrary, net primary productivity (NPP) and crop productivity were lower on this year. The bad yields could be explained, on one hand by the drought in April 2007 that induced abnormally small flag leaves, on the other hand by cloudy and humid conditions from end May to harvest, that induced an assimilation reduction due to low radiation and favoured disease development. The simultaneous higher GPP and lower NPP and productivity in 2006-2007 raise the question of carbon allocation. It suggests that the excess carbon assimilated in 2006-2007 was not stored in grain or straw and thus that it would have been stored in the roots or in vegetation parts that decompose before the harvest. Further biomass measurements (and especially root biomass) are necessary to confirm this hypothesis.Impact de la gestion culturale et du climat sur les flux de CO2, le développement et le rendement de grandes culture

Impact of climatic conditions on a winter wheat (Triticum aestivum Sp.) crop : interannual variability of CO2 fluxes, plant growth and crop yield

This study analyses the interannual variability of carbon dioxide fluxes, growth and productivity of a winter wheat (Triticum aestivum L.) crop. Two growing seasons (2004-2005 and 2006-2007) were compared. Continuous eddy covariance fluxes, leaf scale photosynthesis measurements and crop development monitoring were performed during the two vegetation seasons until harvest at the Lonzée (Belgium) experimental site. The winter wheat was sown and harvested at similar dates (about mid-October and in early August); crop management by the farmer was similar and corresponded at standard. Globally, the two years were characterised by a higher than normal air temperature (9.9 °C and 11.9 °C against 9.4 °C) and lower than normal rainfalls (595.1 mm and 675.1 mm against 772 mm). In addition, 2006-2007 was characterised by exceptionally mild and dry winter and spring. This induced not only earlier growth stages but also a larger Gross Primary Productivity. On the contrary, lower Net Primary Productivity and crop productivity were observed on this year. This could be explained, on one hand by the drought in April 2007 and on the other hand to cloudy and humid conditions from end May to harvest. The first induced a stress in wheat plant which produced an unusually small flag leaf. The second induced an assimilation reduction due to low radiation and favoured disease development. The higher GPP and the lower productivity in 2006-2007 raise the question of carbon allocation. We supposed that, as the excess of carbon assimilated in 2006-2007 was not stored in grain or straw, it should have been stored in the roots. However, our biomass measurements did not allow confirming this hypothesi