Papers by Michael Dingkuhn
Field Crops Research, Aug 1, 1991
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Authorea (Authorea), Jun 2, 2023
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Les caracteristiques physico-chimiques et rheologiques du beurre de cacao dependent dans une larg... more Les caracteristiques physico-chimiques et rheologiques du beurre de cacao dependent dans une large mesure de sa teneur en acides gras libres (AGL). Depuis quelques annees, une augmentation sensible de l'acidite du beurre de cacao en provenance de la Cote d'Ivoire a ete observee de facon recurrente. Cela entraine a la fois des pertes financieres pour le producteur et des surcouts de traitements pour les beurriers. Bien que jamais reellement demontre, le role des lipases a ete avance pour expliquer la formation des AGL. L'etude a pour objectif d'identifier et caracteriser le complexe enzymatique mis en cause. Une lipase a ete mise en evidence dans la poudre de cacao delipidee. Son activite est optimale a deux pH (5,2 et 7,4), laissant supposer la presence de deux lipases ou d'un systeme iso enzymatique. Elle presente une preference marquee pour le beurre de cacao par rapport a d'autres matieres grasses telles que l'huile d'olive et l'huile de soja. Son expression est 3 a 4 fois plus importante dans la poudre de cacao que dans l'extrait proteique. Pour des cacaos sains, aucun des facteurs tels que genotype, degre de maturite des cabosses, delai d'ecabossage, duree de fermentation et stockage prolonge du cacao (etuve climatique - 27°C, HR 75%) n'a permis l'obtention d'echantillons a forts taux d'AGL ni d'activite lipasique importante. En revanche, les feves defectueuses (feves noires, feves collees) et les brisures presentent des teneurs en AGL elevees. Ces teneurs augmentent au cours du stockage. La comparaison de la teneur en microflore et en particulier des moisissures des feves saines et des feves defectueuses ou brisures, avant ou au cours du stockage, montre une relation entre niveau de contamination et teneur en AGL. Parmi la mycoflore, ont ete identifies par ordre d'abondance et de frequence: Absidia corymbifera, Rhyzopus oryzae, Penicillium chrysogenum, Aspergillus flavus, A. tubingensis, A. tamarii et Monilia sp. La formation des AGL du beurre de cacao ne provient donc vraisemblablement pas d'une autolyse enzymatique, mais (exclusivement ?) d'une source microbienne en combinaison avec d'autres facteurs tels que la qualite des feves de cacao, leur etat physique et leurs conditions de stockage. (Resume d'auteur)
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HAL (Le Centre pour la Communication Scientifique Directe), 2001
La recherche d'une efficience maximale de l'intrant, d'une pollution minimale du mili... more La recherche d'une efficience maximale de l'intrant, d'une pollution minimale du milieu et d'une limitation de la sensibilite de la culture aux maladies suppose le pilotage des apports d'azote le mieux adapte localement. La recherche developpe donc des methodes mieux adaptees a la diversite des situations. Leur mise en oeuvre en milieu paysan suppose que l'on puisse disposer d'indicateurs simples et fiables du statut azote de la culture. La relation entre la quantite de biomasse aerienne et la teneur critique en azote de celle-ci, qui a ete verifiee sur le riz irrigue, permet de definir un indicateur de nutrition azotee, INN. La possibilite d'utiliser un outil de mesure de la teneur en chlorophylle, le chlorophyll meter, a ete bien etudiee. Un seuil de valeur Spad au-dessous duquel il convient d'apporter de l'azote a ete defini. Il existe egalement des methodes d'evaluation du statut azote de la culture a partir d'une charte de couleur des feuilles, Leaf color chart ou Lcc. Une experimentation comparant cinq varietes de riz a ete conduite sur la station de l'Irri aux Philippines pour tester ces trois indicateurs. Ils apparaissent finalement assez complementaires : l'INN pourrait permettre de preciser, sur un ensemble relativement restreint de donnees experimentales, un mode simple de calibration destine a interpreter l'information delivree par le chlorophyll meter. Celui-ci, en retour, donnerait acces a un echantillon beaucoup plus vaste, necessaire a la mise au point de la Lcc, et a la definition des conditions de son utilisation et de l'interpretation des donnees qu'elle permet de recueillir
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Agricultural and Forest Meteorology, 2020
Calibration is an essential step for all crop modeling studies. The goal of this study was to com... more Calibration is an essential step for all crop modeling studies. The goal of this study was to compare three commonly-used calibration methods including Ordinary Least Square (OLS), Markov chain Monte Carlo (MCMC), and Generalized Likelihood Uncertainty Estimation (GLUE) as applied to the CSM-CERES-Rice phenology model of the Decision Support System for Agrotechnology Transfer (DSSAT). The analysis was performed by considering goodness-of-fit to observations, calibrated parameter values, uncertainty of parameter estimates and predictions, and the practical implementation of methods. The results showed that the selection of the calibration method has some impacts on parameter estimates and uncertainty quantifications. In the situations where goodness-of-fit is the main criterion, OLS is the fastest and most effective method. When the uncertainty of parameter estimates and model predictions are important, the MCMC method is more reliable in quantifying uncertainties. We found that for predicting phenology in our study, the GLUE method was unrealistic in quantifying model uncertainty, because the default model error variance was unlikely small. This study showed that MCMC for model calibration, coupled with estimation of model error variance, is a promising method for quantifying prediction uncertainty and that MCMC should be incorporated into crop modeling platforms.
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HAL (Le Centre pour la Communication Scientifique Directe), 2012
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Research Square (Research Square), Jun 9, 2021
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Agriculture in the Sudano-Sahelian zone is heavily dependent on the seasonal characteristics of r... more Agriculture in the Sudano-Sahelian zone is heavily dependent on the seasonal characteristics of rainfall, i.e. onset, length and termination of the wet season, seasonal rainfall totals and intraseasonal rainfall distribution. This study seeks to characterize components of regional climatic variability and their impact on simulated, attainable, plot-level yields of millet. First, we will characterize at a regional scale two main events in the seasonal pattern of the monsoon over West Africa by using a daily rainfall dataset over the 1968-1990 period, that is, (1) the "onset" of the summer monsoon characterized by an abrupt northward shift of the ITCZ from 5°N to 10°N around the 24th June, and (2) large and coherent, intra-seasonal rainfall fluctuations at two different spectral windows, between 10 and 25 days and between 25 and 60 days. Second, we will investigate the impact of these regional phenomena on local crop yields using SARRAH, a crop model simulating water-limited yield, by means of sensitivity analyses. The response of attainable yield (limited by climate and water resources but not mineral nutrition) to sowing date was studied for 19 years of the 1968-1990 period for a 90-day millet crop at Niamey. Yield variability is analysed with respect to the apparent validity of regional (climatic) and local (rainfall events) decision criteria for sowing date, while taking into consideration interannual variability of rainfall and intra-seasonal dry spells. Results indicate that information on regional climate dynamics might help improve crop production locally. (Resume d'auteur)
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... statistiques. Communication. Agents Cirad, auteurs de cette publication : BonnalVincent Es ... more ... statistiques. Communication. Agents Cirad, auteurs de cette publication : BonnalVincent Es / UMR TETIS; Combres Jean-Claude Bios / UMR AGAP; Dingkuhn Michaël Bios / UMR AGAP; Flori Albert Bios / UMR AGAP; ...
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In West African Soudano-Sahelian areas, agriculture is highly vulnerable to climate and populatio... more In West African Soudano-Sahelian areas, agriculture is highly vulnerable to climate and populations suffer recurrent food crises related to droughts. To cope with climate variability majority of farmers still crop local photoperiod sensitive varieties [1] having medium grain yield potential (around 2500 kg.ha-1) and low harvest index, under traditional non-intensive practices (no fertiliser, neither pesticide, own seeds, no tillage in many situations, sandy soils, fertility managed through crop rotation and/or manure) [2]. For those areas yields forecasting tools improvement is an important challenge. Yet, addressing the question of climate impacts on crops requires measurements at regional scale [3] and adaptation of crop models. Those issues were addressed within AMMA project from 2005 to 2009, aiming at adapting the SarraH crop model [4] to farmers varieties, assessing and understanding farmers yields, and improving yield forecasting methodology using SarraH. Studies were carried out in Senegal, Mali, Burkina Faso and Niger, in 8 meso-scale sites (from 2.500 to 10.000 km2 each) with different agroclimatic (from 400 to 1000 mm annual rainfall) and agricultural features.
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Abiotic stresses such as salinity affect rice yield components and grain quality. A new, automate... more Abiotic stresses such as salinity affect rice yield components and grain quality. A new, automated methodology is presented to analyze grain weight, length and width distributions for grain samples. Frequency distribution analyses on the basis of histograms generally gave bimodal patterns for grain weight (filled and unfilled grains) and monomodal patterns for grain dimensions. These histograms permit the distinction of unfilled, partially filled and fully filled grains. Peak shape and location on the histogram provide further information potentially useful for the diagnostics of physiological stresses affecting grain hull development, spikelet fertility and filling, and may be of value in breeding and grain quality research. The methodology was applied to rice grain samples taken from farmers' fields having different levels of soil salinity in the Camargue delta region in France. High salinity levels were associated with an increased fraction of unfilled spikelets and reduced grain dimensions and weight, which point at salinity affects taking place largely before flowering during hull development. The methodology is being completed with a biometric tool for histogram analysis, and will be extended to other stresses and germplasm. (Resume d'auteur)
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... climatologie. Chapitre d'ouvrage. Agents Cirad, auteurs de cette publication : Baron... more ... climatologie. Chapitre d'ouvrage. Agents Cirad, auteurs de cette publication : Baron Christian Es / UMR TETIS; Bonnal Vincent Es / UMR TETIS; Dingkuhn Michaël Bios / UMR AGAP; Maraux Florent Persyst / UPR SCA. ...
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Zenodo (CERN European Organization for Nuclear Research), Dec 1, 1999
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Papers by Michael Dingkuhn