A Portable Method for Plant-Available Potassium Determination in Soil

Brazilian territory is vast and mostly of the soil are acidic and poor in macronutrients (NPK). As a result, it is necessary to use high amounts of fertilizers to ensure good productivity. Extraction of available K from soil is usually done using Mehlich-1 solution and determination by inductively coupled plasma optical emission spectrometry (ICP OES). This work proposes a simple and robust method for available K extraction, allowing its determination in a fast and practical way by electrode ion selective (ISE-K), using low volume and less toxic reagents, aiming to be in accordance with the principles of Green Chemistry and portability. Considering these assumptions, available K extraction from soils with different characteristics was done using NaCl solution. The precision of the method is better than 10% and the agreement of the results varies from 80 to 100% in relation to those obtained by the Mehlich-1 solution and K determination by ICP OES. In this way, it was possible to determine the available K content in different types of soil in a fast, practical and robust way, using accessible and low-cost reagents. Therefore, the method can be used for K determination at the field.