FACTEURS QUI INFLUENCENT LA TENEUR DE LA MATIERE ORGANIQUE ET LES PROPRIETES D'ECHANGE CATIONIQUE DES HORIZONS Ap DES SOLS DE GRANDE CULTURE DU QUEBEC

The objectives of this work were (1) to determine the relation existing between the organic matter contents of Ap horizons and their respective soil Orders, (Gleysolic and Podzolic), texture, pH and geographic locations in the different thermal regions of Quebec and (2) to determine the role of organic matter and soil texture on the cation exchange properties of the same Ap horizons coming from soils used for forage crops in Quebec. The cation-exchange capacity (CEC), the exchangeable bases and acidity were determined by using 1 N NH4OAC – pH 7. The results showed a variation in the carbon content ranging from 1.4 to 6.9%. The heat units accumulated in each region and the clay contents were correlated with the percentage of carbon and nitrogen. Soil pH and soil Orders (Gleysolic vs. Podzolic) did not seem to affect the organic matter content. The cation-exchange capacity (CEC) ranged from 10.6 to 42.6 meq/100 g soil; 40% of this was attributable to carbon and 32% to clay contents. Simple and multiple regression equations showed that carbon was correlated with the exchangeable acidity, while clay was related to the exchangeable bases. The CEC of organic matter and clay were respectively 161 ± 45 meq/100 g organic matter and 29 ± 6 meq/100 g clay. These values, lower than for Western Canada, reflected the nature of the organic matter that is less developed in Eastern Canada than in the Chernozemic soils; they also showed the effect of the predominant illite mineral found in the clay fractions compared to montmorillonite in Western Canada.