La matiére organique soluble à l'eau chaude et la stabilityé de l'agrégation. Aspects méthodologiques et application à des sols ferrallitiques du Congo

Abstract

Resume La stabilitye de la structure des horizons de surface et de profondeur de sols ferrallitiques du Congo est etudiee en fonction du mode de gestion des terres et de la teneur en carbone organique total des echantillons. Le role du carbone soluble a l'eau chaude dans l'agregation est appreciea partir de deux approches experimentales, impliquant des extractions apres chauffage en etuve ou en autoclave. Pour ce faire, des comparaisons sont faites entre les taux des macroagregats stables (>200 pm) a l'eau froide et a l'eau chaude. Les resultats indiquent que les situations culturales etudiees induisent des variations significatives des teneurs en carbone total. Le taux des macroagegats stables a l'eau froide est tres fortement correle aux teneurs en carbone total et en carbone solubilisea l'eau chaude. Toutefois, les taux des macroagregats stables obtenus avant et apres extraction du carbone a l'eau chaude ne sont pas significativement differents, ce qui peut remettre en question les resultats sur la fonction agregeante des matieres organiques solubles, deduits des seules approches statistiques. Hot-water soluble organic matter and aggregate stability. Methodological aspects and application to ferrallitic soils of the Congo Summary The structural stability of surface and deeper horizons of ferrallitic soils of the Congo was studied in relation to the land use and the total organic carbon content of the samples. The role of hot-water soluble carbon in aggregation was assessed with two experimental approaches, one by heating in an oven and the other in an autoclave under pressure. The proportion of aggregates (> 200 mum) stable in cold water were compared with that of macroaggregates stable in hot water. Cropping situation sunder study induced significant variations in total carbon content. Aggregate stability was highly correlated with both soluble and total carbon contents. However, amounts of water-stable aggregates obtained before and after solubilization of organic matter in hot water were not significantly different. This result would infirm the supposed aggregating role of soluble organic matter, inferred from statistical data only.