Potassium Fixation Capacity of Chernozems after a Single Application of Potassium Fertilizers in Varying Doses

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Potassium fixation capacity has been estimated in chernozem samples taken from the variants of a field experiment with a single application of potassium fertilizers (0, 70, 140 and 280 kg/ha) after a six-year break in fertilizer use. The potassium fixation capacity of chernozems inferred from the change of exchangeable potassium content after the incubation of the samples with a fixed dose of a potassium fertilizer (50 mg/100 g) ranged from 45 to 47 mg/100 g, or 91–95% of the potassium introduced in the different experimental variants. The actual potassium fixation capacity may be considerably higher than the values measured. Potassium fixation capacity inferred from the change of non-exchangeable potassium content after incubation of the samples with a fixed dose of a potassium fertilizer ranged from 32 to 38 mg/100 g, or 64–75% of the potassium introduced, in the experiment variants. Elevated mobility of fixed potassium in the case of a stronger treatment (2 M HCl, the Pchelkin procedure) and the associated decrease in the difference between the mobile potassium levels before and after incubation with a specific dose of the element may be used to explain this discrepancy. No reliable differences with regard to the average values of potassium fixation capacity were detected between the experiment variants, but the maximal values were observed in the control variant and decreased gradually as the fertilizer doses increased.