Abstract
Potassium (K) is one of the major nutrient elements needed by plant in large quantity for growth and development. This study was carried out on three parent materials (sandstone, shale and alluvium soils) to determine the amount of potassium (K+) released in soils and to find the best fitting model to describe K+ release. Ten grams (10g) of soil was suspended in 20ml of 0.01m Cacl2 at various K concentrations viz: 0, 50, 100, 150, and 200 mgL-K.. These were shaken at 25oC, centrifuged and the concentration of K in the extract was determined. The soil samples were shaken repeatedly each time a fresh solution was added and the process repeated at 1, 2, 4, 8, 16, 32, 64 and 128 hrs. The physical and chemical properties of the soil were also determined. The result showed a variation in soil texture as in Sandstone (sandy loam with high sand content of 74.2%), Alluvium (sandy clay loam with high silt content of 13.0%) and Shale (sandy clay with high clay content of 33.4%). The pH of the soil was moderate; values ranged from 5.0 to 5.4. Salt levels were low: varying from Shale (0.02dsm-1) < Sandstone (0.07 dms-1) < Alluvium (0.08dms-1). Organic matter was moderate varying from Sandstone (4.8gkg-1,) Alluvium > (4.2 gkg-1) > Shale (3.4 gkg-1). Nitrogen was low, available phosphorous was moderate, varying from Sandstone (22.0 mgkg-1) > Alluvium (10.5 mgkg-1) > Shale (8.7 mgkg-1). The most fertile soils indicated by base saturation varied as follows: Shale (86.6%) > Sandstone (80.6%) > Alluvium (65.2%). Results also showed an increased rate of K released with the concentration of K added and the extraction hours. The concentration of K released based on the different models were: Shale (0.106 mgkg-1) > Sandstone (0.040 mgkg-1) >Alluvium (0.027 mgkg-1) for parabolic diffusion model; Alluvium (3.119 mgkg-1) > Sandstone (2.853 mgkg-1) > Shale (2.454 mgkg-1) for power function model; Sandstone (3.654 mgkg-1) > Alluvium (3.545 mgkg-1) > Shale (2.916 mgkg-1) for Eluvich model. The release of K were in these trend; Alluvium > Sand stone > Shale. For the parabolic diffusion R2 = 0997 and for the Eluvich model R2 = 0997. The two models were best fitted models in describing K release with the highest coefficient of determination. The two models are recommended in assessing K availability in the soils studied.