Crop monitoring information is essential for food security and to improve our understanding of the role of agriculture on climate change, among others. Remotely sensing optical and radar data can help to map crop types and to estimate biophysical parameters, especially with the availability of an unprecedented amount of free Sentinel data within the Copernicus programme. These datasets, whose continuity is guaranteed up to decades, offer a unique opportunity to monitor crops systematically every 5 to 10 days. Before developing operational monitoring methods, it is important to understand the temporal variations of the remote sensing signal of different crop types in a given region. In this study, we analyse the temporal trajectory of remote sensing data for a variety of winter and summer crops that are widely cultivated in the world (wheat, rapeseed, maize, soybean and sunflower). The test region is in southwest France, where Sentinel-1 data have been acquired since 2014. Because Sentinel-2 data were not available for this study, optical satellites similar to Sentinel-2 are used, mainly to derive NDVI, for a comparison between the temporal behaviors with radar data. The SAR backscatter and NDVI temporal profiles of fields with varied management practices and environmental conditions are interpreted physically. Key findings from this analysis, leading to possible applications of Sentinel-1 data, with or without the conjunction of Sentinel-2, are then described. This study points out the interest of SAR data and particularly the VH/VV ratio, which is poorly documented in previous studies.

Land management and land-cover change have impacts of similar magnitude on surface temperature" (2014). Papers in Natural Resources. 554.

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Abstract. Temperate grasslands account for c. 20% of the land area in Europe. Carbon accumulation in grassland ecosystems occurs mostly below ground and changes in soil organic carbon stocks may result from land use changes (e.g. conversion of arable land to grassland) and grassland management. Grasslands also contribute to the biosphere±atmosphere exchange of non-CO 2 radiatively active trace gases, with¯uxes intimately linked to management practices. In this article, we discuss the current knowledge on carbon cycling and carbon sequestration opportunities in temperate grasslands. First, from a simple two-parameter exponential model ®tted to literature data, we assess soil organic carbon¯uxes resulting from land use change (e.g. between arable and grassland) and from grassland management. Second, we discuss carbon¯uxes within the context of farming systems, including crop±grass rotations and farm manure applications. Third, using a grassland ecosystem model (PaSim), we provide estimates of the greenhouse gas balance, in CO 2 equivalents, of pastures for a range of stocking rates and of N fertilizer applications. Finally, we consider carbon sequestration opportunities for France resulting from the restoration of grasslands and from the deintensi®cation of intensive livestock breeding systems. We emphasize major uncertainties concerning the magnitude and non-linearity of soil carbon stock changes in agricultural grasslands as well as the emissions of N 2 O from soil and of CH 4 from grazing livestock.

No abstract

Temperate grasslands account for c. 20% of the land area in Europe. Carbon accumulation in grassland ecosystems occurs mostly below ground and changes in soil organic carbon stocks may result from land use changes (e.g. conversion of arable land to grassland) and grassland management. Grasslands also contribute to the biosphere±atmosphere exchange of non-CO 2 radiatively active trace gases, with¯uxes intimately linked to management practices. In this article, we discuss the current knowledge on carbon cycling and carbon sequestration opportunities in temperate grasslands. First, from a simple two-parameter exponential model ®tted to literature data, we assess soil organic carbon¯uxes resulting from land use change (e.g. between arable and grassland) and from grassland management. Second, we discuss carbon¯uxes within the context of farming systems, including crop±grass rotations and farm manure applications. Third, using a grassland ecosystem model (PaSim), we provide estimates of the greenhouse gas balance, in CO 2 equivalents, of pastures for a range of stocking rates and of N fertilizer applications. Finally, we consider carbon sequestration opportunities for France resulting from the restoration of grasslands and from the de-intensi®cation of intensive livestock breeding systems. We emphasize major uncertainties concerning the magnitude and non-linearity of soil carbon stock changes in agricultural grasslands as well as the emissions of N 2 O from soil and of CH 4 from grazing livestock.

Summary• Stem and branch respiration of 30-yr-old Fagus sylvatica trees was measured in a temperate forest for 1 yr to estimate the annual flux at the stand level.• The seasonal response of respiration to air temperature was determined using infra-red gas analysis (IRGA) systems. Annual respiration was derived from half-hourly temperature recording and allometric relations established for the same forest.• The basal respiration rate at 15 ° C (R15) increased greatly during the growing season. On a volume basis, monthly means of R 15 were higher for branches than for stems. For stems, Q 10 was relatively constant throughout the year, with an annual average of 1.7. Estimated annual respiration was approx. 325 g C m -2 ground surface area yr -1 with 50% of this amount attributed to growth respiration.• Stem and branch respiration played a major role in the annual carbon balance of the beech stand. It represented approx. one third of the ecosystem-level carbon loss from respiration. The magnitude of crown respiration makes it obvious that information on branch respiration characteristics is required for reliable estimations at the stand level.

Long term flux measurements of different crop species are necessary to improve our understanding of management and climate effects on carbon flux variability as well as cropland potential in terrestrial carbon sequestration. The main objectives of this study were to analyse the seasonal dynamics of CO2 fluxes and to establish the effects of climate and cropland management on the annual carbon balance. CO2 fluxes were measured by means of the eddy correlation (EC) method over two cropland sites, Aurade´ and Lamasque` re, in South West France for a succession of three crops: rapeseed, winter wheat and sunflower at Aurade´ , and triticale, maize and winter wheat at Lamasque` re. The net ecosystem exchange (NEE) was partitioned into gross ecosystem production (GEP) and ecosystem respiration (RE) and was integrated over the year to compute net ecosystem production (NEP). Different methodologies tested for NEP computation are discussed and a methodology for estimating NEP uncertainty is presented. NEP values ranged between 369 33 g C m2 y1 for winter wheat at Lamasque` re in 2007 and 28 18 g C m2 y1 for sunflower at Aurade´ in 2007. These values were in good agreement with NEP values reported in the literature, except for maize which exhibited a low development compared to the literature. NEP was strongly influenced by the length of the net carbon assimilation period and by interannual climate variability. The warm 2007 winter stimulated early growth of winter wheat, causing large differences in GEP, RE and NEE dynamics for winter wheat when compared to 2006. Management had a strong impact on CO2 flux dynamics and on NEP. Ploughing interrupted net assimilation during voluntary re-growth periods, but it had a negligible short term effect when it occurred on bare soil. Re-growth events after harvest appeared to limit carbon loss: at Lamasque` re in 2005 re-growth contributed to store up to 50 g C m2. Differences in NEE response to climatic variables (VPD, light quality) and vegetation index were addressed and discussed. Net biome production (NBP) was calculated yearly based on NEP and considering carbon input through organic fertilizer and carbon output through harvest. For the three crops, the mean NBP at Aurade´ indicated a nearly carbon balanced ecosystem, whereas Lamasque` re lost about 100 g C m2 y1; therefore, the ecosystem behaved as a carbon source despite the fact that carbon was imported through organic fertilizer. Carbon exportation through harvest was the main cause of this difference between the two sites, and it was explained by the farm production type. Lamasque` re is a cattle breeding farm, exporting most of the aboveground biomass for cattle bedding and feeding, whereas Aurade´ is a cereal production farm, exporting only seeds