Distribution of Forms of Potassium in Soils Cultivated to Shea (vitellaria Paradoxa C.f. Gaertn) Trees at Bida, Niger State, Nigeria

The distribution of potassium forms was studied at Bida, Niger state as part of the Shea butter tree domestication effort of the Nigerian Institute for Oil Palm Research. Soil samples were obtained with the aid of a soil auger at 0-15 and 15-30 cm. The soil samples were air dried, sieved with a 2 mm sieve and analyzed for some physical, chemical and potassium forms using standard methods. Results indicated that a state of dynamic equilibrium exists among the forms of potassium as significant correlations were obtained between total K and difficultly exchangeable K, total K and exchangeable K and total K and residual K with (r = 1.000, P< 0.01), (r = 0.983, P< 0.01), (r = 0.944, P< 0.01)) respectively. In terms of relationship between the forms of K and the particle size distribution of the soils, total K had a very strong relationship with silt with an r2 value of 61.7 % while difficultly exchangeable K had a strong and moderate relationship with silt and clay with r2 values of 65.9 % and 50.1% respectively. Water soluble K had strong relationships with silt and clay with r2 values of 67.5 % and 60.1% respectively. A weak relationship however exists between the forms of K and sand in the soils. While there may not be an urgent K-fertilization need in the soils as revealed by the K-saturation index, the mobile K however showed a moderate K status of the soils. This implies that it might be useful if K fertilization is made at the onset of flowering, a period which corresponds to peak demand in K by crops.