Forms and Status of Potassium in Soils Supporting Rubber (Havea brasiliensis) Plantations in three Locations in Akwa Ibom State, Nigeria

Abstract

The status of the various forms of potassium in soils supporting rubber (Havea brasiliensis) plantations in three locations in Akwa Ibom state was investigated. Soils samples were collected from three rubber plantations (Obio-Akpa, Ntak-inyang and IkotObioEkpung) at the depth of 0 - 15, 15-30, 30-45 and 45-60cm. The results indicated that the soils were loamy sand in texture, acidic with mean pH value of 4.38, low nitrogen (0.16%), exchangeable K (0.09 cmolkg-1), exchangeable Na (0.11 cmolkg^-1) with high content of organic matter (4.80%), calcium (5.68 cmolkg^-1) and magnesium (5.14 cmolkg^-1). The results also revealed that water soluble K ranged from 0.02 to 0.06 cmolkg^-1, available K from 0.05 to 0.15 cmolkg^-1, exchangeable K from 0.03 to 0.10 cmol/kg-1, difficultly K from 0.01 to 0.15 cmol/kg^-1, acid-soluble K from 0.03 to 0.08 cmolkg^-1 and total K from 0.15 to 0.25cmolkg^-1. The different forms of K correlated positively and significantly among each other and with some soil properties, thus an increase in one form lead to a corresponding increase in the other. In all the soils, the content of all forms of K was generally low. The low levels of total K indicate that soils supporting rubber in Obio-Akpa, Ntak-Inyang and IkotObioEkpung in Akwa Ibom State are deficient in K contents and may not meet the needs of K demanding crops like rubber. Therefore, adequate K fertilization is suggested as a possible means of improving the soils for rubber cultivation in the area.