The current paper reports about the influence of different levels of fertilization and agricultural practices (i.e. shallow and deep ploughing) on the total content of potassium (K_tot) and its forms in a soil formed from post-mining lands after twenty seven years of land reclamation processes. The total content of potassium ranged from 11630 to 15890 mg K·kg^-1. It was found that the content of all potassium forms increased in soils along with the level of fertilization and varied within the range between 16.45 and 82.53 mg K·kg^-1 for water-soluble K; between 75.51 and 210.93 mg K·kg^-1 for active K extracted by 0.01 mol·dm^-3 CaCl₂; between 83.56 and 233.42 mg K·kg^-1 for available K determined by the Egner-Riehm method; between 177.24 and 403.86 mg K·kg^-1 for retrograded K extracted by 2 mol·dm^-3 HCl; between 1001,2 and 1765,0 mg K·kg^-1 for the reserve pool of K assayed by 1 mol·dm^-3 HNO₃; and between 1801 and 2817 mg K·kg^-1 for residual K dissolved in a 20% HCl solution. No significant differences occurred for the same fertilization treatments under shallow and deep ploughing practices.

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