PEDOGENESIS ON LOESS AND BASEMENT COMPLEX ROCKS IN A SUBHUMID ENVIRONMENT OF NIGERIA AND THE SUITABILITY OF THE LANDS FOR RAINFED CULTIVATION

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Abstract:

The characteristics of soils developed on loess and basement complex rocks in Funtua were studied with a view to explaining their pedogenesis. The soils were classified and their suitability to crops were evaluated. The soils were generally moderately deep to very deep (68 to 152cm depth); soil depth was of the order basement complex soils < loess – over- basement complex soils < loess soils. The drainage condition is from, poor to well drained, with loess soils being poorly drained, whereas loess-over basement complex and basement complex soils are moderately drained and well drained respectively. The silt dominated the fine earth portion of the soils, except in the basement complex soils where sand dominated. Soil particle density decreased in the order basement complex soils (2.60)> loess – over – basement complex soils (2.58) > loess soils (2.55) Mg m-3 The bulk density ranged from 1.26 to 1.67 Mg m-3 with high surface values. The available water holding capacity (AWHC) of the soils increased in the order basement complex soils (10.77) < loess – over basement complex soils (12.27) < loess soils (14.80) percent and were considered adequate to support plant growth. The soil reaction ranged between very strongly acidic and moderately acidic (pH 4.9 to 5.8). The total exchangeable bases increased in the order; basement complex soils (2.75) < loess – over basement complex soils (3.14) < loess soils (3.81) cmol (+) kg-1. Total exchange acidity, CEC (NH4OAc and clay ) followed the same order. Base saturation was low (<50%) in all soils. The values of soil organic carbon , total nitrogen, available phosphorus were all low but available sulphur was high (> 6mg kg-1 ) in the surface. Statistical analysis showed that these parameters are significantly highly correlated to organic carbon (p=0. 01, .001). Electrical conductivity and exchangeable sodium percent were very low with respective values of less than 0.06 dSm-1 and less than 8%. Free Fe and Mn oxides were low in all the soils (the highest value was 0.75% for Fed). Parent material, topography and drainage had the most pronounced effects on the soil properties. The main pedogenetic processes occurring in the soils are argillation, organic matter mineralization, eluviation, illuviation, leaching, textural and structural differentiation, horizonation, partial migration and crystallization. According to the USDA Soil Taxonomy, all the soils were classified as Kanhaplic Haplustults except pedon L/BC1 which was classified as Ombroaquic Haplustult and Pedon LI as Typic Haplustult. In the FAO/UNESCO Soil map of the World Legend, both basement complex and loess – over – basement complex soils are placed as Haplic Acrisols while the loess soils are classified as Haplic Alisol (Pedon LI) and Haplic Nitisol (Pedon L2). The soils on the three parent materials were grouped into three land units namely land unit one (LU1) for basement complex, land unit two (LU2) for loess-over-basement complex and land unit three (LU3) for loess. All the land units were moderately suitable (S2) for cotton, groundnut and maize, except LU3 which was marginally suitable (S3) for cotton and maize, and was not suitable for groundnut. LU1 and LU2 were highly suitable for sorghum whereas LU3 was moderately suitable by virtue of its poorly drained nature.

PEDOGENESIS ON LOESS AND BASEMENT COMPLEX ROCKS IN A SUBHUMID ENVIRONMENT OF NIGERIA AND THE SUITABILITY OF THE LANDS FOR RAINFED CULTIVATION

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