Biddappa, C.C.Cecil, S.R.Khan, H.H.2014-07-162014-07-162007-02Symposium on potassium for plantation crops. Bangalore (6-8 November, 199d)http://hdl.handle.net/123456789/4176Coconut is generally cultivated in acid laterite, lateritic and red soils where the K content is low. The critical level of soil potassium is between 0.15 to 0.20 me 100g, equivalent to 59-78 ppm of potassium. Based on the assumption that about 80 ppm K is needed to maintain the optimum K content in the diagnostic leaf (0.8-1.0%) a desorption equilibrium model has been developed for laterite and sandy loam soils from which site specific recommendations can be successfully made. The absorption of K by coconut not merely depends on the absolute K concentrations in situ but it depends on relative concentrations of Na+, Mg++, Ca** and NH4+ in the soil. This is primarily because of the antagonism offered by these ions in the uptake of K by coconut. The selective distribution of applied K in the soil indicated that the major portion of K would be held in the boiling HN03 fraction followed by IN NH4OAc extractable form. The desorption studies showed that about 80% of the applied K could be desorbed within 2-3 extractions and further desorption is very steady upto 10 subsequent extractions.enArticle