Perspectives d'amélioration du conseil prévisionnel de fertilisation azotée à la parcelle en Wallonie par l'utilisation du logiciel AzoFert®

Prospects for improving the provisional nitrogen fertilization recommendation at field scale in Wallonia using the AzoFert® software. The French software AzoFert® for nitrogen fertilization recommendation is currently under adaptation and validation for soil and climatic conditions in Wallonia by the CRA-W within the INTERREG IV project "SUN" (Sustainable Use of Nitrogen). This adaptation has raised the need for a change of values in the parameter tables and catalogs relating to meadow residues, crop residues, catch crop practices, crops, organic amendments and soil type. Data from 25 trials of increasing nitrogen fertilizer rates conducted by CRA-W between 1996 and 2011 in cereal, potato and vegetable crops located on loam and sandy loam soil were used to validate the AzoFert® software adapted for Wallonia. The difference between nitrogen rates recommended on the one hand by AzoFert® or Azobil® (software currently used in the reference lab for Nitrate [Requasud] at CRA-W) and the optimal dose of nitrogen fertilizer assessed in each trial on the other hand shows that, in most cases, AzoFert® gives a recommendation closer to the optimum than Azobil®. The nitrogen uptake measured in the plants collected in the unfertilized control plot also shows a higher correlation with nitrogen supply from the soil assessed by AzoFert® than for plants assessed by Azobil®. The more accurate estimate of the mineralization of organic sources, probably linked to the dynamic soil nitrogen supply approach integrated into AzoFert®, may explain the gain in the greater accuracy of the AzoFert® recommendation in comparison with that of Azobil®

Les cultures intermédiaires pièges à nitrate (CIPAN) et engrais verts : protection de l'environnement et intérêt agronomique

Autumn cover crops and green manures: environment protection and agronomic interest. Due to the evolution of the environmental policy, practice of green manure cropping has been replaced by autumn cover crops in order to take up nitrate residues of the soil. These crops (mustard, phacelia, rye-grass, rye) show a high ability to take up N (sometimes more than 100 kg N.ha-1), leading to a decreasing threat for nitrate leaching. Such an ability is however related to species, but also to cropping practices mainly sowing date. Subsequent mineralization (measured with labeling 15N technic) of this organic-green manure-N, influenced by physical and chemical characteristics of the ploughed biomass, seems however limited (less than 45% of N ploughed in the soil) and does not lead obviously to a reduction of the N advice for the following crop. Nevertheless, stocking of organic N and C in the soil is expected to have a beneficial long-term effect on both mineralization (providing more N) and soil humus content leading to improve structural properties of soil

Dengue 1 Diversity and Microevolution, French Polynesia 2001–2006: Connection with Epidemiology and Clinics

The molecular characterization of 181 serotype 1 Dengue fever (DENV-1) viruses collected regularly during the 2001–2006 period in French Polynesia (FP) from patients experiencing various clinical presentations revealed that the virus responsible for the severe 2001 outbreak was introduced from South-East Asia, and evolved under an endemic mode until a new epidemic five years later. The dynamics of DENV-1 epidemics in FP did not follow the model of repeated virus introductions described in other South Pacific islands. They were characterized by a long sustained viral circulation and the absence of new viral introduction over a six-year period. Viral genetic variability was not observed only during outbreaks. In contrast with conventional thinking, a significant part of DENV-1 evolution may occur during endemic periods, and may reflect adaptation to the mosquito vector. However, DENV-1 evolution was globally characterized by strong purifying selection pressures leading to genome conservation, like other DENV serotypes and other arboviruses subject to constraints imposed by the host-vector alternating replication of viruses. Severe cases—dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS)—may be linked to both viral and host factors. For the first time, we report a significant correlation between intra-host viral genetic variability and clinical outcome. Severe cases were characterized by more homogeneous viral populations with lower intra-host genetic variability

The Mediterranean Sea Regime Shift at the End of the 1980s, and Intriguing Parallelisms with Other European Basins

Background: Regime shifts are abrupt changes encompassing a multitude of physical properties and ecosystem variables, which lead to new regime conditions. Recent investigations focus on the changes in ecosystem diversity and functioning associated to such shifts. Of particular interest, because of the implication on climate drivers, are shifts that occur synchronously in separated basins. Principal Findings: In this work we analyze and review long-term records of Mediterranean ecological and hydro-climate variables and find that all point to a synchronous change in the late 1980s. A quantitative synthesis of the literature (including observed oceanic data, models and satellite analyses) shows that these years mark a major change in Mediterranean hydrographic properties, surface circulation, and deep water convection (the Eastern Mediterranean Transient). We provide novel analyses that link local, regional and basin scale hydrological properties with two major indicators of large scale climate, the North Atlantic Oscillation index and the Northern Hemisphere Temperature index, suggesting that the Mediterranean shift is part of a large scale change in the Northern Hemisphere. We provide a simplified scheme of the different effects of climate vs. temperature on pelagic ecosystems. Conclusions: Our results show that the Mediterranean Sea underwent a major change at the end of the 1980s that encompassed atmospheric, hydrological, and ecological systems, for which it can be considered a regime shift. We further provide evidence that the local hydrography is linked to the larger scale, northern hemisphere climate. These results suggest that the shifts that affected the North, Baltic, Black and Mediterranean (this work) Seas at the end of the 1980s, that have been so far only partly associated, are likely linked as part a northern hemisphere change. These findings bear wide implications for the development of climate change scenarios, as synchronous shifts may provide the key for distinguishing local (i.e., basin) anthropogenic drivers, such as eutrophication or fishing, from larger scale (hemispheric) climate drivers

Threshold value for chlorophyll meter as decision tool for nitrogen management of potato

We developed a practical system to improve crop N efficiency in potato (Solanum tuberosum L.). It is based on a strategy that includes split applications of N fertilizer and the use of the Hydro N Tester (HNT) leaf chlorophyll meter as a plant N status indicator. The method was tested in 12 potato field trials conducted from 1997 to 2000 on loam and sandy loam soils in Belgium. The fields were fertilized at planting with 70% of a field-specific N recommendation. Because of site-specific effects, raw HNT values measured during the growing season were not useful in assessing the crop N status and the need for supplemental N. In each field, there was a 200-m(2) subplot receiving no N fertilizer to obtain a control HNT value. After harvest, the 12 sites were separated into two groups according to the crop response to increasing N fertilizer rates. A parameter called the HAT slope was determined as the difference between HNT values measured in the field and those from the zero-N plot divided by the applied N rate. This parameter shows low values for sites presenting a weak crop response to N and high values for sites with a strong response. A threshold value to determine the need for supplemental N was found to correspond to a HNT slope value of 0.5. This value was successfully validated on a commercial scale at 10 sites in Belgium in 2001 and 2002 for nonirrigated crops of cultivar Bintje

Gestion de la fertilisation azotée des cultures de plein champ. Perspectives d'amélioration de l'efficience d'utilisation de l'azote sur base du suivi du statut azoté de la biomasse aérienne

Nitrogen fertilization management of open-field crops. Opportunities for improvement of nitrogen use efficiency based on crop nitrogen status monitoring. The improvement of nitrogen use efficiency in crops is currently an important issue in farming due to current and future economical and environmental constraints. Splitting of N fertilizer application is the most suitable approach for providing an optimal match of N need and supply. The implementation of monitoring methods to assess crop N status is required to define the relevant amounts and periods required for split applications. This paper discusses the available methods of split N fertilizer application and their mode of use and implementation. After a short overview of the concept of crop N status, the main existing methods to estimate nitrogen needs are examined for their accuracy, specificity and sensitivity based on research conducted at CRA-W (Production and Sectors Department, Crop Production Systems Unit) over the last two decades, focusing specifically on the potato crop. The methods and the results described relate to the petiole sap nitrate concentration test assessed via a reflectometer, the measurement of leaf chlorophyll concentration with a handheld chlorophyll meter, leaf chlorophyll fluorescence readings with handheld fluorimeters, and the measurement of crop light reflectance with a handheld radiometer (ground-based remote sensing) or with satellite imagery (spatial remote sensing). Conditions for implementing such methods within decision support systems are briefly described, by focusing on the need to use relative values rather than raw values taken from the readings, and also on the requirement for threshold value definition. The integration of crop nitrogen status values into N fertilization recommendation models is illustrated through a Decision Support System created at CRA-W for the potato crop

Utilisation de la fluorescence chlorophyllienne pour l'évaluation du statut azoté des cultures (synthèse bibliographique)

Use of chlorophyll fluorescence for the evaluation of crops nitrogen status. A review. Introduction. Optimizing the nitrogen (N) fertilization of crops requires the use of methods that quickly and accurately assess the N status of aboveground biomass during the growing season. Optical measurements on plants allow the achievement of this goal and, among these approaches, the leaf chlorophyll fluorescence based method (ChlF) appears promising. The potential of ChlF has been studied for many years. The value of this method for detecting and quantifying various biotic and abiotic plant stresses has been assessed as well as its potential for the evaluation of crop N status (CNS). For this last application, ChlF could offer solutions to the limitations of the usual methods for evaluating CNS, which are based on light transmittance or reflectance and are related to leaf chlorophyll content. Literature. In this report, two ChlF based approaches are reviewed. The first approach is variable ChlF, or Kautsky kinetics, which represents the approach taken in the majority of the published work examined in the field of ChlF. The second approach is based on ChlF sensing methods for the estimation of the concentration of leaf metabolite compounds in plants, particularly that of leaf chlorophyll and phenolic compounds (mainly flavonoids). The characteristics and the applications of these two fluorescence approaches are studied for their potential use for the in-season monitoring of CNS. Conclusions. Of these two approaches, the use of the ratio of fluorescence combining the estimation of concentrations of leaf chlorophyll and flavonoid content appears to be a relevant potential method to assess CNS, as both concentrations are in close relationship with leaf N concentration