Cinétique de décroissance de la surface verte et estimation du rendement du blé d'hiver

Estimating winter wheat yield through the decreasing phase of its green area. A large number of agrometeorological models for crop yield assessment are available with various levels of complexity and empiricism. However, the current development of models for wheat yield forecasting does not always reflect the inclusion of the loss of valuable green area and its relation to biotic and abiotic processes in production situation. In this study the senescence phase of winter wheat (Triticum aestivum L.) is monitored through the GAI (Green Area Index), calculated from digital hemispherical photographies taken over plots in Belgium, Grand-Duchy of Luxembourg and France. Two curve-fitting functions (modified Gompertz and modified logistic) are used to describe the senescence phase. Metrics derived from these functions and characterizing this phase (i.e. the maximum value of GAI, the senescence rate and the time taken to reach either 37% or 50% of the green surface in the senescent phase) are related to final grain yields. The regression-based models calculated with these metrics showed that final yield could be estimated with a coefficient of determination of 0.83 and a RMSE of 0.48 t·ha-1. Such simple models may be considered as a first yield estimates that may be performed in order to provide a better integrated yield assessment in operational systems. Indeed, estimation of cereal-crop production, particularly wheat, is considered as a priority in most crop research programs due to the relevance of food grain to world agricultural production

Protection and maintenance of permanent pastures

peer reviewedAll farmers receiving direct payments are subject to compulsory cross-compliance which includes standards related to the maintenance and protection of permanent pastures. Questionnaire techniques and spatio-temporal analyses demonstrated that the ratio of permanent pasture area to agricultural land provides a simple tool for monitoring and controlling the protection of permanent pastures at the regional to Member State level. Huge variations in the ratio across Europe were related to the importance of permanent pastures, the interpretation of definitions, sources of information used, differences in calculation, and the presence of protective and/or sensitive zones. Precautionary or complementary measures are in place in most Member States in order to prevent decreases in the ratio. The implementation of GAEC standards related to permanent pastures overlaps with the standard management requirements, national legislation and current agri-environmental programmes. The study advocates the establishment of a comprehensive geo-information platform consisting of a topologically correct inventory of all permanent pasture parcels in a 1:1 geo-referenced relation between IACS and LPIS; ancillary spatially explicit data such as orthophotos, remote sensing images and other thematic geo-databases; and, geodatabases with parcel information compiled for other monitoring purposes such as those within the framework of the Nitrates Directive or 2nd pillar support

Laboratory, field and airborne spectroscopy for monitoring organic carbon content in agricultural soils

This study explains the potential and the limits of a field ASD spectrometer and a CASI airborne instrument to assess the Soil Organic Carbon, in the context of soil carbon mapping

The Interest Rate and Credit Channels in Belgium: An Investigation with Micro-Level Firm Data

This paper investigates the effects of monetary policy on firms' investment behaviour. The analysis relies on a comprehensive database of Belgian firms covering all sectors of economic activity and firms of all sizes. We proceed in two steps. First, we estimate a reduced-form investment equation derived from the neo-classical model, augmented by cash flow. This equation is estimated by the Arellano and Bond (1991) GMM procedure. Second, we compute the elasticity of the user cost of capital and the cash flow/capital ratio to the policy-controlled interest rate. We estimate the model for various sample splits according to sectors and sizes. Our results indicate that small firms are more sensitive to monetary policy than large firms, and that services are almost unaffected. Since the impact differs across sectors and sizes, we can conclude that monetary policy produces distributional effects

Bulletin agrométéorologique - Septembre 2003

Le mois de septembre a été caractérisé par des précipitations et des vitesses moyennes du vent faibles. Par contre, les températures et le rayonnement furent relativement élevés sur l’ensemble du pays. Cette année, les rendements prévus pour les cultures de maï s fourrager et de betterave sucrière, sont respectivement équivalents et inférieurs à ceux observés en 2002

Bulletin agrométéorologique - Août 2002

Le mois d’août a été caractérisé par des précipitations fortement excédentaires. Les températures et l’humidité furent anormalement élevées, alors que la vitesse moyenne du vent fut exceptionnellement faible et le rayonnement médiocre sur l’ensemble du pays. Les données de terrain disponibles confirment la tendance des prévisions de rendement du bulletin précédent (juillet 2002). La situation des cultures est globalement favorable, avec des rendements qui s’annoncent supérieurs voire similaires à ceux de 2001 à l’exception du colza

Bulletin agrométéorologique - Juin 2003

Le mois de juillet a été caractérisé par des précipitations généralement normales à excédentaires. Les températures, la vitesse moyenne du vent et l’humidité furent proches de la normale. Par contre, le rayonnement fut médiocre sur l’ensemble du pays. Par rapport au bulletin précédent (juin 2002), les prévisions de rendement n’ont pas changé. La situation des cultures est globalement favorable, avec des rendements qui s’annoncent supérieurs voire similaires à ceux de 2001 à l’exception du colza

Bulletin agrométéorologique - Juillet 2002

Le mois de juillet a été caractérisé par des précipitations généralement normales à excédentaires. Les températures, la vitesse moyenne du vent et l’humidité furent proches de la normale. Par contre, le rayonnement fut médiocre sur l’ensemble du pays. Par rapport au bulletin précédent (juin 2002), les prévisions de rendement n’ont pas changé. La situation des cultures est globalement favorable, avec des rendements qui s’annoncent supérieurs voire similaires à ceux de 2001 à l’exception du colza

Can hyperspectral techniques improve estimates of carbon stocks in agricultural soils ?

peer reviewedSoil organic carbon (SOC) represents one of the major pools in the global carbon cycle. However, fluxes of CO2 from soils into the atmosphere by respiration or inversely sequestration of CO2 through photosynthesis and subsequent immobilisation in the form of humus are difficult to quantify. In principle changes in SOC stock over time reflect CO2 fluxes. The detection of these stock changes, however, require intensive sampling mainly due to the large spatial variability of SOC both within individual fields and larger units with similar soils and land use. The aim of this paper is to evaluate the potential of airborne-hyperspectral techniques using a CASI sensor and hand held Near Infrared Spectroscopy (NIRS) with an ASD spectrometer to conduct SOC inventories of individual parcels. During a field campaign in the Belgian Ardennes during Octobre 2003, more than 120 sites on a regular grid within 13 freshly ploughed fields were selected. At these sites, field spectra of the bare soil have been measured and samples from the topsoil were taken. SOC content (Walkley and Black), soil moisture and bulk density of these samples have been determined. As a first step, the soil reflectance has been transformed (log (1/R), Savitsky-Golay smoothing and derivative, gap derivative, moving average) in order to filter the spectral responses and to eliminate noise. Then, we used both stepwise and partial least square (PLS) regression analysis to relate these spectra to measured SOC contents. Regression models performed much better when the data were divided in two sub-groups representing different moisture conditions of the soil surface. These statistical model calibrations were validated on an independent data set. Standard Error of Prediction (SEP) ranged from 0.19 to 0.24 % carbon for the field spectra determined using the ASD depending on soil moisture of the surface layer. This is a little bit more than the reproducibility error inherent to the Walkley and Black analysis. Airborne CASI techniques performed less well mainly due to the narrow spectral range. Tests on airborne CASI+SASI hyperspectral data from a previous field campaign [1] showed better results. Overall, low bias allowed the use of spectral techniques to estimate population means with a high confidence level. The spectral techniques have a strong potential in determining changes in carbon tock change studies. The large within field variability of SOC content precludes the assessment, using conventional soil sampling, of SOC changes as a result of management (1 t C ha-1 yr-1) over a reasonable time period (5 years). Depending on the variance of the SOC content measured in the field ( 2 = 11-166 t C ha-1), we need 16-210 samples to detect a change. Since this number of samples is rarely available for individual fields, conventional sampling methods can only be used for larger spatial units containing many fields. In contrast, the airborne-hyperspectral technique and portable NIRS are able to supply these large amounts of data, and can thus improve the accuracy of SOC stock assessments of individual fields. This in turn will result in a smaller detection limit of SOC stock changes

Use of mineralization kinetics to estimate the agricultural value of a compost incorporated into a vineyard in Luxembourg.

peer reviewe