Potassium is one of essential macronutrients for plant nutrition. Of the primary plants nutrients, the potassium is known regarding to its influence on the production in general and in particular on the quality of the harvest. To achieve high and good quality yields, potassium fertilization is a factor of utmost importance. Unfortunately in agriculture are used large quantities of nitrogen at the expense of potassium, causing an imbalance because the amount of potassium that is extracted with the yield is much higher than the one that is returned to the soil as fertilizer. This draws decreased soil fertility in terms of a reduced nutrient content. From field experiment soil samples were taken by depth of 0-20 cm for testing. Analysis were made in Soil Science Laboratory of Agricultural Faculty. Potassium was extract in ammonium acetat –lactat solution, and content determination was made by emission with atomic absorption spectrophotometer Varian 220 FAAS, at wave length of 766 nm. pH was determined in water extract 1:2.5. Ammonia is extracted from the soil with a solution of potassium sulphate (K2SO4) 0,1n, soil solution ratio being 1:3 and it is been colorimetrical dosed with Nessler's reagent. Potassium availability for plants is governed by the transfer between four main pools in the soil: native, fixed, exchangeable and soluble. The main contributors to K supply to plants are exchangeable and soluble forms. When K+ is removed from the solution by plant uptake or leaching, the soil solution is rapidly replenished by K+ from exchangeable sites, whereas the fixed clay replenishes the exchangeable sites slowly by a diffusion controlled process. Usually average values of state insurance of assimilable potassium in the arable layer of chernozem cambic, are between 150-200 ppm, which corresponds to a medium and good insurance in this macroelement. There is a reduction in the potassium content of the soil at low pH values. As the pH is close to the neutral values, soil content of assimilable K increases.

Key words: potassium, soil, fertilization, ammonium

Presentation: oral