Potential of Potassium Supply in Locally Available Soil Amendments for Use in Coconut Plantations

Potassium (K) is an essential macro nutrient which plays a vital role in crop growth and development. Most of the tropical soils are having low level of potassium and crops grown on these soils are heavily dependent on mineral fertilizers for the supply of potassium. Organic growers are in need of locally available natural source of potassium as they have restrictions on use of synthetic fertilizers. A pot experiment was conducted on sandy regosol to investigate the potassium supplying ability to soil from locally available potassium containing materials. The treatments were, T1-Control (no amendments added), ground mica (T2), feldspar (T3), coconut husk ash (T4), Tithonia diversifolia (T5), muriate of potash (T6) for comparison. Materials were analyzed for nutrient content and applied at the rate equivalent to recommended K level for adult coconut palm. Soil samples were extracted from each pot at one-month interval for analysis. Results show that higher exchangeable K level has been maintained (1.5-3.8 meq/100g soil) by T4 during the experimental period while T1, T2, T3 and T6 had significantly lower (<0.05 meq/100g soil) exchangeable K. In addition, T4 has increased soil pH towards neutral level and higher exchangeable Mg and available P. Treatments T5 and T4 also showed significantly higher exchangeable K than T1, T2 and T3. The results indicate that coconut husk ash and Tithonia diversifolia have a greater potential to be used as a source of potassium with additional advantage of enhanced availability of other nutrients.