Özet:

: This study was undertaken to examine the influence of the sowing date, sowing density, and split spring application of nitrogen (N) fertilizer on plant density, tillering, yield components, and grain yields of winter wheat ( Triticum aestivum L.) grown in northeastern Poland between 2018 and 2021. The experiment had a split-plot design with three sowing dates (early (3–6 September), delayed by 14 days, and delayed by 28 days), three sowing densities (200, 300, and 400 live grains m −2), and three split spring N rates (40 + 100, 70 + 70, and 100 + 40 kg ha −1 applied in BBCH stages 22–25 and 30–31, respectively). The number of spikes m −2 increased by 11% on average when winter wheat was sown with a delay of 14 days (17–20 September) and 28 days (1–4 October). The number of spikes m −2 was highest when winter wheat was sown at 300 and 400 live grains m −2. The application of 100 + 40 kg N ha −1 (BBCH 22–25 and 30–31, respectively) increased the number of spikes m −2. An increase in sowing density from 200 to 300 to 400 live grains m −2 decreased the number of grains spike −1 by 5% and 7%, respectively. Thousand grain weight (TGW) increased by 1% and 2% when sowing was delayed by 14 (17–20 September) and 28 days (1–4 October), respectively. In northeastern Poland, grain yields peaked when winter wheat was sown between 17 September and 4 October (10.52–10.58 Mg ha −1). In late-sown winter wheat, grain yields increased due to a higher number of spikes m −2 and higher grain weight. The highest sowing density (400 live grains m −2) induced a greater increase in grain yields than the lowest sowing density (200 live grains m −2) (10.25 vs.10.02 Mg ha −1). In winter wheat sown at a density of 400 live grains m −2, the increase in grain yields resulted in a higher number of spikes m −2. Grain yields peaked in response to 100 kg N ha −1 applied in BBCH stages 22–25 and 40 kg N ha −1 applied in BBCH stages 30–31 (this split N rate increased the number of spikes m −2). In turn, the highest straw yield (6.23 Mg ha −1) was obtained when the second split of N fertilizer was applied in BBCH stages 30–31 (40 + 100 kg N ha −1). Straw yields decreased significantly (by 6%) when winter wheat was sown late (early October). Delayed sowing (mid-September and early October) increased the harvest index (HI) of winter wheat by 5–7%. Split spring N application influenced grain and straw yields, but it had no effect on the HI of winter wheat.

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