QUANTIFICATION OF SOIL TEXTURAL FRACTIONS OF BAS-ZAIRE USING SOIL MAPPOLYGONS AND OR POINT OBSERVATIONS

Reconnaissance soil surveys typically produce qualitative choropleth m aps and descriptions of sampled soil profiles, These can be converted to quantitative information directly. Alternatively quantitative predi ctors can be made by interpolating between the point observations, or the two can be combined. Three methods to predict the sand and clay co ntent of Bas-Zaire using a reconnaissance soil map and 151 soil profil es are compared. A cross-validation showed that the combination method produced the most precise predictions with an acceptably small bias. This result was obtained only after verifying and correcting the soil surveyor's estimations of the soil map prediction variances and strati fying the area to acquire a relative pooled within-stratum variogram.