Soil phosphorus and potassium availability in long-term field experiments with organic and mineral fertilization

The effect of organic, mineral and combined organic and mineral fertilization of soils on the winter wheat yields and nutrient contents in soils was evaluated in long-term field experiments. Two sites with different soil characteristics were evaluated - Lukavec u Pacova (cambisol) and Ivanovice na Hane (degraded chernozem). The type of fertilization influenced wheat yields. Nutrient uptake by winter wheat was higher under nitrogen (N) fertilization, which resulted in a negative balance of phosphorus (P) and potassium (K) and to a decrease of nutrient contents in the more fertile soils at Ivanovice na Hane. Two soil tests (Mehlich 3 method and NH4-acetate method) were used to determine P and K availability. The mineral nitrogen fertilization negatively and significantly affected NH(4-)acetate extractable concentrations of nutrients in the soils and these were lower in comparison with concentrations of P and K determined by Mehlich 3 method. Relative availability of P in alkaline soils from Ivanovice treated with mineral N increased while the soil pH decreased.