Availability indices of potassium in an ultisol under coleus cultivation

Abstract

A field experiment was carried out in the main campus of College of Horticulture, Kerala Agricultural University, Vellanikkara to study the availability indices of potassium in an Ultisol under the coleus cultivation. The experiment was laid out in a randomized block design with eight treatments and three replications. The treatments consisted of eight different levels of potassium. All other crop management practices were done uniformly in all plots as per the recommendation of KAU. Observations on biometric parameters as well as yield attributes were recorded during the cropping period. The soil, shoot and tuber were analysed for the various nutrients. The quantity of potassium extractable by various reagents was also estimated at these three stages. The Q/I parameters were estimated for the soil under study and the thermodynamic parameters related to K supplying power of soil were worked out.

Tuber number and tuber yield were significantly influenced by the potassium application up to 60 kg K2O ha-1. The size of the tuber was not significantly affected with potassium application. Available potassium status that increased linearly with the levels of K did not affect the availability of P where as availability of N increased during the active growth stage of the coleus. Available potassium increased significantly with the levels of K application. Availability of exchangeable Al and Mn in soil got reduced with the increased levels of K. Even though the nitrogen and potassium content in shoot increased with the levels of K application at active stages of crop growth it had not reflected in the final yield. Calcium and aluminium absorption were found to reduce with increase in available K. Nitrogen and phosphorous content in the tuber reduced towards the harvest of crop. Calcium and magnesium content in tuber was influenced by K application where as K content in tuber was not increased with the levels of K.

At all stages of analysis the quantity of K extracted with all reagents increased with the levels of potassium application in the soil. The water soluble, exchangeable and non-exchangeable potassium were reduced from initial stages towards harvest indicating the crop utilization and the presence of dynamic equilibrium between the various forms of potassium. Correlation studies conducted between yield attributes and quantity of K extracted revealed positive correlation between tuber yields and tuber number with water soluble and exchangeable K. The quantity-intensity parameters estimated at temperatures viz. 25°C and 40°C showed that the desorption of potassium is more at higher temperature indicating the higher availability of K in summer season. The potassium adsorption of soil under study followed the Freundlich adsorption isotherm both at 25°C and 40°C.