Les lipides libres des sols sous formations naturelles au Burkina Faso : Nature, origine et relation avec quelques facteurs de fertilité
Résumé
Free lipids extracted from the surface horizon of ten soil profiles were studied in order to enhance the knowledge on these non-humic substances. Profiles were distributed from the sahelian to the south sudanian zones of Burkina Faso. Biological, physical and chemical properties were determined. Lipids, extracted from each sample with chloroform, were derivatised and analyzed using gas chromatography-mass spectrometry (GC-MS). The amounts of free lipids which ranged from 35 to 137mg.kg-1 soil represented less than 1 % of total carbon. Identified compounds were mono-and di-fatty acids (as methyl esters), alcohols (acetylated), alkanes, steroids and hopanoids. These compounds are characteristic of a dominant plant origin. However branched acids and a part of diacids are of bacterial origin. Moreover the amount of free lipids negatively correlates with the sum of exchangeable cations, cations exchangeable capacity (CEC) and useful water supply. However, the amounts of nonadecanoic (C19), palmitic (C16) and stearic (C18) acids are positively correlated, respectively with the previous soil chemical properties, the cumulative carbon mineralization and the carbon from microbial biomass.