Influence of storage time and temperature of air-dried soils on pH and extractable nutrients using 0.01 mol/L CaCl2

The stability of pH and certified amounts of nitrate, ammonia, total soluble nitrogen, total soluble organic carbon, magnesium, sodium, potassium and phosphorus obtained by extraction from air-dried (40 °C) soil samples by 0.01 mol/L CaCl₂ solution during storage at –18 °C, 4 °C, ambient temperature, 40 °C and 70 °C was investigated in one calcareous soil and one acid sandy soil. Even at storage times of 45 and 90 days, extractable amounts changed. Extractable amounts of P, NH₄-N, total soluble N and soluble organic C increased even at a storage temperature of 40 °C. The pH was lower for samples stored at a temperature of 70 °C and also the Mg concentration became lower at elevated storage temperatures after 45 days in both soils. It is suggested that reference materials certified for values using unbuffered extractants should be stored at a temperature not higher than 4 °C. Received: 13 May 1997 / Revised: 16 July 1997 / Accepted: 18 July 1997