THE INTERACTION BETWEEN POTASSIUM AND MAGNESIUM iN RED YELLOW PODZOLIC SOILS WITH LATERITE AND ITS EFFECT ON NUTRITION OF COCONUT PALMS (Cocos nucifera, L.)

Abstract

The interaction between plant available potassium and magnesium inhighly leached red yellow podzolic soils with laterite in Southern coastalarea of Sri Lanka and its effect on coconut palm was studied in a 3x2 KxMgfactorial experiment that consisted of 3 levels of potassium and 2 levels ofmagnesium fertilizer application to coconut palms in plots. Five years aftercontinuation of treatment application, soil samples were taken from top soils(0-20 cm) and sub soils (20-40 cm) at monthly intervals for 10 months andanalyzed for exchangeable potassium and magnesium (1M ammonium acetateextraction at pH 7.0) and water soluble potassium and magnesium (1:10soil/water ratio). Leaf samples taken from the 14* frond at bimonthly intervalswere analyzed for potassium and magnesium.The results showed that the application of potassium fertilizer decreasedthe quantity of both exchangeable and water extractable magnesiumand magnesium fertilizer decreased the quantity of exchangeable potassiumin soils. The mutual decreasing effect on the exchangeable fraction of eachnutrient is attributed to low cation exchange capacity and base saturation ofthe soils. The close association of the coconut leaf nutrient contents with soilnutrient status implies that poor chemical characteristics of red yellow podzolicsoils bring about imbalance of potassium and magnesium nutrition incoconut palms.