Comparative Assessment of Qualitative Land Capability Classification and a Parametric Capability Index Along a Toposequence in Southwestern Nigeria

Land capability assessment provides a broad framework for identifying the degree and nature of land limitations that govern sustainable agricultural use. This study compared a qualitative USDA-type capability classification with a parametric capability index for six pedons distributed across upper-, middle-, and lower-slope positions along a toposequence in Erinmope-Ekiti, southwestern Nigeria. Two profile pits were examined at each slope position, described morphologically, and sampled by genetic horizon for routine physical and chemical analyses. The soils were predominantly sandy loam to clay, with clay commonly increasing with depth. Pedon-level mean pH ranged from 5.36 to 6.38, electrical conductivity from 0.46 to 2.60 dS m−1, organic carbon from 8.57 – 22.80 g kg−1, effective cation exchange capacity from 1.52 to 2.94 cmol kg−1, and base saturation from 59.24 to 94.47%. Under the qualitative system, low ECEC was the principal class-determining soil limitation, and the pedons were classified as Class V; erosion, drainage, salinity and effective soil depth contributed secondary limitations at specific positions. The parametric procedure was implemented using the square-root aggregation equation and the supplied land-quality ratings, produced the capability indices of 13.08, 12.74, 11.32, 12.96, 10.26 and 12.31% for US1, US2, MS1, MS2, LS1 and LS2, respectively. The indices fall within Class VII. The difference between the two outputs arises principally from the aggregation rule: the qualitative approach is controlled by the most severe limitation, while the parametric index compounds the lowest ratings of the major land-quality groups. The results demonstrate that method selection can materially affect the apparent severity of land limitations and that capability interpretation should retain the individual limitation profile rather than rely on the overall class alone. Management should emphasize erosion control, organic-matter maintenance, balanced nutrient management, protection of lower-slope drainage conditions, and monitoring of sites with relatively high electrical conductivity.