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Dernière mise à jour : Mai 2018

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Soutenance HDR

Vendredi 11 Septembre 10h00 Bordeaux Sciences Agro salle MEF1 (extension Amphi C)
Capture d’écran_2020-09-08_10-13-50

Soutenance orale d’Habilitation à Diriger des Recherches

Par L. JORDAN-MEILLE
Maître de conférences en agronomie
Bordeaux Sciences Agro
UMR 1220 ISPA Bordeaux Sciences Agro - INRA

Potassium and plant nutrition : Who K’res?

Devant le jury composé de : Edith Le Cadre Professeure Agrocampus Ouest Rapporteur, Jean-Pierre Sarthou Professeur ENSAT Rapporteur, Jean-Christophe Avice Professeur Université de Caen Normandie Rapporteur, Claude Plassard DR INRAE Examinatrice, Stephan Haefele DR Rothamsted Research Examinateur, Klaus Dittert Professeur Université de Göttingen Examinateur

Résumé

Le potassium (K) est le cation le plus concentré dans les plantes. C’est un élément dont la géochimie est bien connue et dont la mesure de biodisponibilité fait la quasi-unanimité. Il ne pose pas de problème environnemental ou sanitaire particulier, et ses réserves sous forme de sel (KCl) sont très abondantes. Il est cependant parfois négligé dans les programmes de fertilisation, et reste le minéral le plus déficitaire à l’échelle d’immenses régions agricoles où les résidus de cultures sont exportés. Pays riches et pauvres affrontent ainsi des situations de déficiences plus ou moins sévères, causées par des défauts de gestion ou des contraintes économiques. La prédiction de l’évolution des rendements des cultures carencées en K serait une aide significative au raisonnement de la fertilisation, mais les modèles de cultures n’intègrent pas aujourd’hui de module « potassium » dans leurs algorithmes. Des résultats ont été acquis pendant 20 ans sur une dizaine d’expérimentations portant sur 3 espèces (maïs, cotonnier, eucalyptus). Ils sont présentés de manière synthétique, selon un cadre conceptuel empruntant à la modélisation basée sur les mécanismes d’interception/conversion du rayonnement. Les rôles du K sur les processus métaboliques d’une part, de gestion des composantes du potentiel hydrique d’autre part, sont particulièrement décortiqués. Un chapitre spécial est également consacré à l’interaction entre la nutrition potassique et la capacité des plantes à résister aux effets du manque d’eau. Une large revue de littérature, combinée à nos résultats, pointe désormais la nécessité, pour la recherche et le développement, de rénover les bases du raisonnement de la fertilisation, d’améliorer l’efficience d’utilisation des ressources et d’approfondir les interactions biotiques et abiotiques impliquant la nutrition K.

Abstract

Potassium (K) is the most concentrated cation in plants. Its geochemistry is well known, and predicting its availability in soils relies on consensual chemical analysis. K is not associated with any environmental or health issues. Moreover, it is widely stored in the geological layers under high-quality salts. For those reasons, K might appear to be a “boring” mineral, with corollary that K-fertilisation is trivial. Combined with economic issues, this leads developed and developing countries to face K-deficiencies in agricultural soils. On a global scale, K is the most deficient nutrient in agrosystems. Therefore, its management in agrosystems needs to be improved. Lack of K-modelling in current plant growth models is a barrier to developping K diagnosis and fertilisation recommendations. Over the 20 last years, we have conducted 10 experiments to obtain physiological and technical references for plant growth prediction under K deficiencies. All the relevant data are synthesised in this manuscript, based on three species (maize, eucalyptus, cotton), and presented according to an “Interception-Conversion” framework. We have especially tried to determine if the plants’ response to K deficiency was particularly accounted for by its role on water potential components or on metabolic processes. A special chapter is dedicated to the impact of K nutrition on the ability of the plants to cope with the lack of water. Finally, a large literature review, combined with our results, leads us to propose the main perspectives on which K research should focus: improving nutrition concepts and rules, increasing global K efficiency at agrosystem scales, and analysing K nutrition in interaction with biotic and abiotic factors.