L’EFFET DU TEMPS DE L’ECHANTILLONNAGE ET DE L’HETEROGENEITE DU CHAMP SUR LES ANALYSES DE FERTILITE DU SOL

The objective of this work was to determine the effect of sampling time and field heterogeneity on the soil fertility tests (pH, organic matter, N, P, K, Ca, Mg). The sampling on Ap horizons was repeated in May, July and October of 1976 at 25 locations of a clay loam soil (Kamouraska Series) and a sandy soil (Vien Series). The results indicated that the coefficients of variation were lower than 7% for the pH analyses but exceeded 30% for the other analyses. For the latter, sampling time showed a significant decrease in the P, K and Mg values from May to October on the sandy soil but showed no effect on the clay loam soil. Field heterogeneity was found to be a greater factor of variation than sampling time. It explained an average of 26% of the variation obtained on the sandy soil and 74% on the clay loam soil where the cultural practice of raising the center of the field, for better surface drainage, caused great variations in the depth of the Ap horizons in relation to the width of the field.