IPI K Centre - Measurement and Assessment of Soil Potassium

Soils have to be fertile to be productive, whether that means producing forest, grassland or agricultural crops. Fertile soil has the ability to hold reserves of many available essential plant nutrients, including potassium. This nutrient retention depends on the clay and organic matter in soil; potassium does not leach except to some extent from very sandy soils. The reserve of potassium provides a secure store which is available to the crop as it grows.

Soil tests are indispensable to monitor the soil fertility status. Testing soil for its content of plant available nutrients has been common practice for many decades. The basic principle to estimate the availability of K is to replace K from the exchange sites with an excess of another cation such as NH₄ as ammonium acetate or nitrate, or with calcium (Ca) as calcium lactate or chloride. The soil K determined by this method is the so-called exchangeable K (Kex), or "readily available" soil K. Less frequently used methods are soil extraction with diluted HCl, with resins or with the help of a low electrical voltage in the Electro Ultra Filtration (EUF) method. A review of the different agents for extraction of soil K is given in the IPI Research Topics No. 4 by MUTSCHER (1995)

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