The aim of the research was to determine the effect of constant mineral fertilization with NPK and diversified fertilization with Fe and Mo microelements on the nitrogenase activity, alfalfa yield and nitrogen content and uptake with yield. A three-year (2012-2014) field experiment was carried out on research fields owned by the Siedlce University of Natural Sciences and Humanities, Poland. The experiment was set up in a completely randomized design with four replications. The first factor consisted of fertilization treatments: control, NPK, NPKFe1, NPKMo1, NPKFe1Mo1, NPKFe2, NPKMo2, NPKFe2Mo2. The second factor was composed of the years of research (first, second and third year). Nitrogenase activity in the soil samples was determined. The dry matter yield and total nitrogen content in alfalfa were determined and the nitrogen uptake with yield was calculated. Statistical calculations demonstrated a significant effect of the examined factors on the model amount of nitrogen fixed by Rhizobium meliloti bacteria living in symbiosis with alfalfa and free-living bacteria. The significantly highest mean amount of nitrogen was calculated for alfalfa fertilized with NPKFe1Mo1 (618 kg ha-1). The calculated model amounts of fixed nitrogen were by an average 4.5% higher than the values describing the nitrogen uptake with alfalfa dry matter yield. The significantly highest activity of nitrogenase was found in the soil fertilized with NPKFe1Mo1 (20-22-124.5-0.5-0.5 kg ha-1) collected in September 2012 (563.5 nM C2H4). The research demonstrated that the fertilization of alfalfa with NPKFe1Mo1 is optimal to achieve the best parameters of the analysed characteristics (except the nitrogen content).      

24.1.2019