Influence of long-term fertilizer application on changes of the content of Mehlich-3 estimated soil macronutrients

The aim of this work is to evaluate the changes of Mehlich 3 P, K, Ca and Mg contents in soil during a long-term field experiments with sewage sludge, farmyard manure (FYM) and mineral NPK (NPK) application, compared to the control non-fertilized treatment. The experiment was established at the Humpolec and Suchdol sites (Czech Republic). Potatoes, wheat and barley were grown in crop rotation. Fertilizing system was based on the same nitrogen dose of 330 kg N/ha per one crop rotation. Archive soil samples from the beginning of the experiment (1996) and from the end of each year's crop rotation (1999, 2002, 2005, 2008 and 2011) were analyzed. In spite of the different soil-climatic conditions of the studied sites, very similar tendencies of P, K, Ca and Mg contents changes after the fertilizing systems used were observed in the soil. In case of the same nitrogen dose (330 kg N/ha), sewage sludge appeared to be better source of bioavailable soil phosphorus compared to the farmyard manure and NPK. On the contrary, FYM was a better source of bioavailable potassium and magnesium, despite the lower total magnesium content in FYM. The NPK treatment was the best long-term source of bioavailable potassium.