Physiological and Productive Responses of Soybean Cultivars to Nitrogen Fertilization

The aim of the study was to determine the effect of cultivar and nitrogen fertilization on the morphological and physiological traits and yield of soybean (Glycine max (L.) Merrill) grown in central-eastern Poland. In a strict, two-factor field experiment, four soybean cultivars were used: ‘Abelina’, ‘Malaga’, ‘Coraline’ and ‘Petrina’, and three nitrogen rates: 0, 30 and 60 kg N ha-¹. A moderate rate (N30) was applied before sow-ing, while the higher rate (N60) was divided into two parts, with 50% applied before sowing and 50% top-dressed at BBCH 61. The studies were conducted during two growing seasons. It was shown, that both the cultivar and nitrogen fertilization signif-icantly affected plant height, leaf area index (LAI), leaf greenness index (SPAD) and chlorophyll fluorescence indices (Fv/Fm, PI). The interaction among cultivar, fertiliza-tion, and years was significant for several physiological parameters, indicating a strong influence of environmental factors on plant response. Nitrogen fertilization in-creased plant height and chlorophyll content, but reduced fluorescence indices. Among the cultivars studied, 'Malaga' was characterized by the highest physiological activity and seed yield, while 'Abelina' had the lowest values for these parameters. The appli-cation of a moderate rate of nitrogen (N30) im-proved the physiological indicators of plants and elements of yield structure without reducing potential photochemical effi-ciency of PSII, while a higher rate (N60) did not result in a significant increase in yield, despite a greater number of pods and seeds per plant, which may have been due to a reduction in the thousand seed weight. The results obtained indicate, that moderate nitrogen fertilization, combined with the right choice of cultivar, can help to increase the physiological efficiency and yield stability of soybeans in temperate climates.