A Comparative Analysis of Fractionation of Potassium in Soils from Some Refuse Dumpsites in Benin City Nigeria

A study on potassium dynamics and fractionation was carried out in Benin City to determine the amount and distribution of k fraction in soil samples collected from different refuse dumpsites. The sand, silt and clay contents of the dumpsites soils varied from 83.3 to 95.3, 0.60 to 3.35 and 2.55 to 15.10%, respectively. Soils were dominantly sandy with textural classes varying from sand to loamy sand down at depth. The result revealed that the water-soluble k and Exchangeable k range from 163.8 to 643.4 mg/kg in surface soils and 271.1 to 319.8 mg/kg in sub-surface in Benin-Onitsha Bypass and Benin-Warri Bypass. The difficult exchangeable k content ranged from 93.6 to 483.6 mg/kg and 50.1 to 467.9 mg/kg .in the surface and sub-surface of the dumpsites; K content was highest in the subsurface soils than in surface soils due to high deposition of refuse from surface soils within the dumpsites. In general, distribution of K forms decreased in the order reserved K > fixed > water-soluble > Exchangeable K, Structural K > Diff. Exch. K as well as the mobility factor for each of the refuse dumpsite investigated. Similarly, the amount of the various forms of k extracted decreased as the soil pH decreased. The soil samples collected far away from the dumpsites have lower concentrations of k forms compared to those from the vicinity of the dumpsites. This shows that the waste dumps had higher concentration of elements, thereby interacting with the soil and enhance their dominance within the dumpsites. The particle size fraction of the refuse dump suggests the need for consideration of active soil portions for sustainable K management of the environment.