AN EVALUATION OF THE ACCURACY OF A 25-YEAR OLD SOIL MAP FROM SOUTHERN NIGERIA

The accuracy of a 25-year old soil map was assessed. Purity was found to be 70%, coefficient of variation (CV) range was found to be between 4% for Base Saturation (BS) and 84% for Bray 1 available phosphate (P) for soil association and between 3% (BS) and 55% (P) for soil series. F-tests showed that seven of the eleven soil properties examined were effective in discriminating mutually exclusive series (p less-than-or-equal-to 0.01), while five of these (Sand, Clay, Ca, ECEC and BS) were effective in discriminating among associations. Intra-class correlation coefficient (r(i)) ranged between 0.41 and 0.86 for seven properties within series map units and were 0.22 in the association units. Data for the compliment of relative variance (1-RV) showed that soil series accounts for 80-84% of the total variance in the soil properties while the association accounts for 15%. The results indicate that the quality of a well executed soil map can remain high for long periods even in an area with high influence of land use and management.