EFFECT OF SOWING DATE ON THE YIELD AND SEED QUALITY OF SOYBEAN [GLYCINE MAX (L.) MERR.]

Soybean is a photophilic and thormophilic plant with short-day photoperiodism. Therefore, special attention should be paid to proper seed sowing in soybean agriculture practice. The aim of the experiment was to evaluate soybean response to different seed sowing time points. The main plots were three sowing dates scheduled each year at about 10-day intervals (19/04/2016, 29/04/2016, 9/05/2016, 13/04/2017, 24/04/2017, 2/05/2017, 16/04/2018, 27/04/2018, 7/05/2018). Subplots were three soybean varieties: Aldana, Merlin and Lissabon. Weather conditions varied in years and had an effect on the study results obtained. The early date of sowing reduced plant density before harvest in comparison with later sowings. The growing season of plants shortened as the sowing date was delayed. The early sowing date increased the number of pods per plant and thousand seeds weight (TSW) in relation to the optimal time point. Protein content in seeds was significantly higher after sowing the seeds in a delayed period compared to the early date. The early sowing date increased the content of phosphorus and potassium in the seeds. The yield of seeds, protein and fat did not vary depending on the sowing date. However, they varied in the successive years of research. In 2017, plots with a delayed sowing date gave a significantly higher seed yield compared to the early date. The early variety Aldana yielded significantly lower than the mid-early varieties Merlin and Lissabon. The low SPAD index (soil plant analysis development) and high LAI index (leaf area index) were determined in the variety Lissabon.