Profile distribution of total and available Sulphur and boron in sandy soils of Nigerian semi-arid savanna .
The total and available sulphur and boron forms were determined in sandy soils formed from sand dunes, sandy alluvial terrace and sandstone formation in northwestern Nigeria. Hot water and Morgan’s solution (sodium acetate/acetic acid solution buffered at pH 4.8) were used as extractants for available boron while calcium phosphate solution was the extractant for available sulphur. In the surface horizons, in all the sandy soils, total boron ranged from 2.03 to 170.85 mg kg-1 soil, while subsoil values varied from 0.59 to 135 mg kg-1 soil. The means of the total boron are highly significantly (p=0.001) different among the sandy soils. The means of hot water extractable boron (Bhw) are also significantly (p=0.05) different for the sandy soils. Generally boron values are significantly higher in the surface horizons than in the sub-surface horizons. In terms of magnitude, the sandy soils may be arranged as follows: Rabah terrace > Wurno sandstone > Sangiwa dunes > Illela dunes > Sokoto dunes. The mean values of calcium phosphate extractable sulphur are significantly (p=0.05) different among the sandy soils. Values in the surface horizons are also generally higher than the sub-surface horizons. The values of Sc are higher in the sand dune soils than the sandstone and terrace soils within the study area. By the critical limits of 0.1 to 0.2 mg kg-1 given in the literature for Nigerian savanna soils, the sandy soils understudied appear to be slightly above this limit especially for the terrace and sandstone soils. For the sand dune soils the surface horizons are marginally adequate but the subsoils are below the critical limit. If the
critical limit of 4 mg kg-1 quoted in the literature is considered, all the sandy soils understudied are deficient in available sulphur except for soils derived from Illela sand dune, which are only marginally sufficient. For optimum crop production on sandy soils within the study area, sulphur and boron addition through the use of boronated single supper phosphate and other sulphur-based fertilizers should therefore, be encouraged.