POTASSIUM CONTENT IN MAIZE AND SOIL FERTILIZED WITH ORGANIC MATERIALS

Since potassium is essential for plant nutrition, should this element be deficient in sewage sludge used for plant fertilization supplementary mineral potassium fertilization is necessary. The aim of the present study has been to evaluate the effect of fertilization with organic materials on maize yield, its potassium concentrations and the content of bioavailable forms of potassium in soil of different grain size distribution. The impact of fertilization on potassium concentrations in maize was examined in a 3-year, two-factor pot experiment (the factors were soil and fertilization). The grain size distribution of the test soil material was weakly loamy sand (psg), sandy silt loam (gpp) and medium silt loam (gsp). Sewage sludge originated from two different municipal mechanical and biological sewage treatment plants. Mixtures of sewage sludge with peat were prepared at a gravimetric ratio 1:1 converted to material dry matter. For chemical analyses the plant material was mineralized in a muffle furnace (at 450 degrees C for 5 firs) and the remains were dissolved in diluted nitric acid. Bioavailable potassium was determined with Egner-Riehm method in the soil material, which was dried and sifted through a 1mm mesh sieve. Potassium was determined by flame photometry in solutions of the plant material and soil extracts. Fertilization with sewage sludge and mixtures with peat had a more positive effect on maize yield than fertilization with mineral salts. In comparison with organic materials supplied to the soil, mineral salt treatment significantly increased potassium content in maize biomass. Mineral supplementation of potassium introduced with organic materials and its balancing did not increase soil abundance in bioavailable potassium in comparison with the initial abundance, although a diversified soil response to the applied fertilization was observed.