Abstract

                                The present study was aimed at finding out the validity of a number of soil tests for K. using different extractants by relating them to uptake. The experiments were conducted in red and black soils of Coimbatore, under field conditions. creating -varying levels of soil potassium in mini-plots under natural agro-climatic conditions so as to be valid for field trials. Two crops, onion and maize were chosen as test crops to study the plant factors. Nine different methods besides the Neubauer test were used for assessing the availability. None of the soil test methods. tried in the present study. was universally suitable for all the crops and soils. Neubauer test was found to be not useful in black soil for both the crops although in red soil it was useful in the case of maize. From the study. it therefore appears that unless certain norms are evolved to include plant and soil characteristics the estimation and adoption of available K index to predict K avallability and uptake have very little practical value.

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