Le raisonnement de la fertilisation azotée du blé a, depuis 40 ans, été largement orienté par le consensus autour de la méthode du bilan, avec comme principes fondamentaux : une nutrition azotée non limitante tout au long du cycle et l’estimation, de manière indépendante, des différents termes de l’équation du bilan pour caractériser la fourniture du sol et les besoins en azote de la plante. Au regard des enjeux de réduction des pollutions environnementales, de l’évolution des exigences qualitative du marché, ainsi que des difficultés de mise en oeuvre de la méthode, on s’interroge sur l’opportunité de renouveler ce paradigme. Pour proposer une nouvelle méthode qui réponde aux divers enjeux concernant l’azote, qui valorise au mieux les connaissances disponibles et dont la mise en oeuvre est cohérente avec les moyens des acteurs, nous avons mis en oeuvre une démarche de conception innovante, structurée en 3 étapes : un diagnostic des usages des outils actuels, une phase de conception, incluant des ateliers de conception et la mise au point de règle de décision à l’aide d’un modèle, et un test d’usage du prototype conçu.Le diagnostic des usages a mis en évidence plusieurs obstacles à la mise en oeuvre de la méthode du bilan, dont la fixation de l’objectif de rendement, ce qui a orienté la phase de conception vers l’exploration d’un concept de méthode de fertilisation azotée permettant de s’en affranchir. La méthode mise au point est basée sur le suivi régulier de l’état de nutrition azotée de la plante, l’acceptation de carences en azote non préjudiciables et des règles de décision tenant compte des conditions météorologiques au moment de l’apport. Nous montrons que la conception a rendu nécessaire la production de nouvelles connaissances, mais aussi la diversification des ressources et des compétences habituellement mobilisées. Ce travail enrichit les méthodes de conception d’outils d’aide à la décision en montrant comment l’articulation des 3 étapes permet de sortir du paradigme qui domine la fertilisation azotée depuis des décennies et d’élaborer un outil palliant les défauts des outils actuels. / Decisions about nitrogen fertilizer application on wheat have, for the last 40 years, been based on the balance sheet method, with the following underlying principles: non-limiting nitrogen nutrition throughout the crop cycle, and independent estimation of the various terms of the equation, to characterize soil nitrogen supply and plant nitrogen needs. Environmental pollution, changes in the qualitative requirements of the market and difficulties implementing this method have raised questions about whether it might be appropriate to switch to new ways of managing nitrogen fertilizer. We developed a new method meeting the diverse constraints relating to nitrogen use, making the best use of available knowledge and easily applicable by users, through a 3-steps innovative design approach: a diagnosis of the use of current tools, a design phase including design workshops, production of new knowledge, a modelbased prototyping, and the testing of a prototype method.The diagnosis of uses identified several barriers to the implementation of the balance sheet method, including the need to set a target yield. This directed the design phase towards the exploration of new ways of managing nitrogen fertilizer that did not require the fixing of a target yield. The method developed is based on the regular monitoring of plant nitrogen nutrition, the toleration of periods of nitrogen deficiency that are not prejudicial and the use of decision rules taking weather conditions at the time of nitrogen application into account.This design required the generation of new knowledge and a diversification of the resources and skills usually mobilized. This work enriches the methods for designing decision support tools and shows how a combination of 3 steps can be used to develop a tool for managing nitrogen fertilizer applications completely different from the dominant paradigm of the last 40 years, and compensating the defects of current methods.

The original publication is available at http:/www.plosone.org / Introduction: The utility of T-cell based interferon-gamma release assays for the diagnosis of latent tuberculosis infection remains unclear in settings with a high burden of tuberculosis. Objectives: To determine risk factors associated with positive QuantiFERON-TB Gold In-Tube (QFT-GIT) and tuberculin skin test (TST) results and the level of agreement between the tests; to explore the hypotheses that positivity in QFT-GIT is more related to recent infection and less affected by HIV than the TST. Methods: Adult household contacts of tuberculosis patients were invited to participate in a cross-sectional study across 24 communities in Zambia and South Africa. HIV, QFT-GIT and TST tests were done. A questionnaire was used to assess risk factors. Results: A total of 2,220 contacts were seen. 1,803 individuals had interpretable results for both tests, 1,147 (63.6%) were QFT-GIT positive while 725 (40.2%) were TST positive. Agreement between the tests was low (kappa = 0.24). QFT-GIT and TST results were associated with increasing age (adjusted OR [aOR] for each 10 year increase for QFT-GIT 1.15; 95% CI: 1.06-1.25, and for TST aOR: 1.10; 95% CI 1.01-1.20). HIV positivity was less common among those with positive results on QFT-GIT (aOR: 0.51; 95% CI: 0.39-0.67) and TST (aOR: 0.61; 95% CI: 0.46-0.82). Smear positivity of the index case was associated with QFT-GIT (aOR: 1.25; 95% CI: 0.90-1.74) and TST (aOR: 1.39; 95% CI: 0.98-1.98) results. We found little evidence in our data to support our hypotheses. Conclusion: QFT-GIT may not be more sensitive than the TST to detect risk factors associated with tuberculous infection. We found little evidence to support the hypotheses that positivity in QFT-GIT is more related to recent infection and less affected by HIV than the TST. © 2011 Shanaube et al. / Publishers' Version