Influence of gypsum treatment on extractability of nutrients from soils

In an incubation experiment with 36 soils we tested the influence of application of 3.3 g of CaSO4 center dot 2 H2O per kg of soil on extractability of nutrients (P, K, Mg, Ca, Mn, B and S). After 134-day incubation of gypsum-treated soils the soils were extracted with water (1:5, w/v), 0.5M ammonium acetate with NH4F addition (pH 7) and by Mehlich 3 method. An ICP-technique was used for nutrient detection and colorimetry on a SKALAR analyser was employed to determine phosphates and sulphates. The most interesting results were measured in phosphorus. P concentration was markedly lower in the H2O extract after gypsum treatment, on average by 69% in ICP detection and by 58% in colorimetric detection of phosphates. A significant depression of P concentration was also measured in the acetate extract, but it was considerably lower (11% in ICP detection, 14% in colorimetry). On the contrary, in Mehlich 3 extraction the concentration after gypsum treatment was higher on average by 31% in ICP detection while colorimetry detection did not show any significant differences. The results indicate that it is necessary to identify the method of soil extraction including the method of analytical determination of the nutrient, when the nutrient status of soils is to be evaluated.