For characterizing the rate of increase of the available soil phosphorus content applying superphosphate fertilization the slope of the linear regression curve in the range of 0–12–120 ppm P is used. The available phosphorus is determined by NH4‐lactate and NaHCO3extractions. The rate of increase of available phosphorus is primarily influenced by the presence of CaCO3and is in close correlation with the pH, as well as the silt + clay content. The rate of decrease of available phosphorus in time after P fertilization in non‐calcareous soil is similar, in calcareous soil is different measured by the two extractions.