Evaluation of surface soil quality and land suitability for agricultural soils affected by soil erosion

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Soil erosion is an important environmental factor affecting most agricultural lands, particularly dryland areas where vegetation cover is limited. This study, based on two assessments, was aimed to evaluate the physical impact of soil erosion in dryland areas of Kebbi State, Nigeria. Soil erosion was assessed according USDA-NRCS and FAO guidelines for visual assessment and based on visual soil erosion approach (VSEA). In the first assessment, six types of soil erosion were reported: sheet, rill, gully, winnowing, mass-movement and dry-mechanical. These six types of soil erosion were identified as slight, moderate or severe degrees of impact. Additionally, eight different shapes of rill and gully erosion were classified based on their physical appearance and the nature of their surface soil textures as C, I, J, S, U, V, X and Y. The V, U and Y categories described gully erosion under a uniform sand-silt soil texture, whereas the C, I, J, S and X categories described rill erosion under a sandy loam soil texture. In the second assessment, erosion was classified according to its category and degree of impact for soil quality and land suitability descriptions under the proposed specific VSEA. The results show that the soil quality classes of the study sites are Sq1, Sq2, Sq3, and Sq4 or Sq5, and were identified as very slight, slight, moderate and highly moderate or severe degrees of impact, respectively. However, the land suitability classes were rated as Ls1, Ls2, Ls3, Ls4 and Ls5 corresponding very well to good land, moderately good land, poorly good land, very poor land and bad land, respectively. The estimated impact was recorded from 226 to 555 cm for width and from 116 to 213 cm for depth. It is concluded that the soil quality and land suitability for agricultural production, are physically damage as a result of the rate of rill and gully erosion. Therefore, the study suggested an adaptation of traditionally based conservation practices such as mixed-cropping, zero tillage and shelter-belt to diminish the impact in the study sites.