Вплив строків та норм висіву на зимостійкість гібридів ріпаку озимого (Brassica napus L.)

One of the economically attractive export crops in Ukraine is winter rape (Brassica napus L.). Due to the wide range of uses of its processed products in the world, the area under this crop in Ukraine is growing from year to year. It is known that the survival of rapeseed in winter is complicated by the fact that the loss of grass can be caused by one or more abiotic and biotic factors, including poor plant survival, low temperatures and their duration, dry soil, and damage by diseases and pests. Therefore, the study of seeding rates and sowing dates for winter rape to increase the level of winter hardiness is an urgent task for domestic science. Although rapeseed is a winter crop, it can be quite sensitive to a sharp drop in air temperature, especially in the absence of snow cover. Such risks arise in the second half of the winter period, when most of the carbohydrates accumulated in the root system have already been used to maintain plant life. An important agrotechnical measure that directly affects the wintering of winter rape plants is the choice of seeding rates and timing. The choice of these indicators depends on many factors, ranging from the biology of the crop to the immediate conditions of the area. Therefore, farmers should choose winter rape hybrids based on their initial growth rate and winter hardiness. One of the indicators of successful preparation of winter rape plants for wintering is the average number of formed leaves per plant. It was noted that at the optimal sowing time in the Pancher hybrid, the number of leaves was in the range of 7.4–9.7 pcs./ plant, while for the Fencer hybrid — 8.2–10.6 pcs./ plant. At late sowing dates, the number of leaves in the Pancher hybrid decreased to 6.2–8.5 pcs/plant, while in the Fencer hybrid — to 7.3–9.4 pcs/plant. At the optimal sowing time with a rate of 500 thousand units/ha, the diameter of the root collar of winter rape hybrids was 0.82–0.84 cm, while the height of the growth point above the soil level was 2.18– 2.35 cm. It was noted that a decrease in the seeding rate from 500 to 200 thousand units/ha reduced intraspecific competition for light, moisture and nutrients. Therefore, in these variants, there was an increase in the thickness of the root collar by 30– 35% and a decrease in the height of the growth point above the soil level by 12–20%. Cultivation of winter rape hybrids at optimal sowing dates contributed to the fact that the survival rate of plants during the winter period was 86.3–88.1% at a sowing rate of 500 thousand units/ha, 89.0–89.4% at 400 thousand units/ha, 90.2–90.4% at a rate of 300 thousand units/ha and 91.5–92.0% at a rate of 200 thousand units/ha. At late sowing dates, there was a slight overall decrease in the survival rate by 0.5–2.2%. However, there was no significant difference in the level of survival between Pancher and Fencer hybrids.