Balance of potassium in two long-term field experiments with different fertilization treatments

Balance of potassium (K) was observed in long-term stationary field experiments (21 years) at two sites with different soil and climatic conditions (Luvisol, Cambisol). The following crops were rotated within the trial: potatoes- winter wheat-spring barley. All three crops were grown each year. The trial comprised 6 treatments: (1) no fertilization; (2) farmyard manure; (3) half dose of farmyard manure + nitrogen (N) in mineral nitrogen fertilizers; (4) mineral nitrogen fertilizers; (5) NPK in mineral fertilizers; (6) straw of spring barley + N in mineral nitrogen fertilizers. The recovery rate of potassium from farmyard manure by crops was 24-26%, from mineral fertilizers it was 27-52%. Different fertilization intensities were manifested by significant differences in the content of exchangeable K in soil. Changes in non-exchangeable K (Kne) were recorded only at the Luvisol site (850 mg Kne/kg), but not at the Cambisol site (3000 mg Kne/kg). The maximum negative balance (-2376 kg K/ha/21 years) was recorded at the mineral nitrogen fertilization treatment.