The Seed Yield of Soybean Cultivars and Their Quantity Depending on Sowing Term

The successful production of soybean seeds is dependent on the sowing date, because every sowing outside of the optimal time contributes to losses of yield. The aim of the study was to identify the response to sowing date of the chosen soybean cultivars by the evaluation of the length of the soybean vegetation period, yield level, its parameters and seed chemical composition. A field experiment was conducted in the years 2016-2019 at the Agricultural Experimental Station in Grabow (Masovian Voivodeship, Poland) belonging to the Institute of Soil Science and Plant Cultivation- State Research Institute in Pulawy. Soybean cultivars (four in 2016-2017 and six in 2018-2019) listed in the EU Common Catalogue with various earliness were included in the experiment. Three different sowing dates were used: I-early, II-medium and III-delayed. The two-factor experiment was carried out using a split-plot design on Luvisol soil with sandy loam texture classes, in four replications. Soybean seeds were inoculated with a bacterial culture Nitragina containing strains Bradyrhizobium japonicum. After reaching full maturity, the most important morphological traits of 10 plants and yield components: the number of pods per plant and the number of seeds per pod were provided. After harvest, the seeds yield (kg per hectare at the 14% moisture), and 1000-seed weight were determined. The study showed that in the years with favourable weather conditions during the growing season the best yields were obtained for soybean sown on the second date, while in the year with unfavourable weather conditions, the sowing date had no significant effect on the yields. Seeds of the soybean cultivars grown under conditions of limited rainfall contained about 9% more protein than those grown under more favourable agroecological conditions. The delay of sowing date by about 20 days positively influenced the accumulation of protein in seeds.