Theoretical justification of multipolarity of sowing dates for winter rape

Abstract

Goal. To study and justify the feasibility and direction of optimizing the timing of sowing winter rape. Methods. Field (setting up the experiment, conducting treatments), mathe- matical and analytical (identifying similarities or differences in indicators was determined by mathematical processing using the method of analysis of variance). Results. Two- year studies conducted in 2021-2022 in the Steppe of Ukraine showed that under favorable vegetation conditions, the sowing date of winter rapeseed has a significant impact on its productivity and, thus, the optimum can manifest itself within 50-60 days, which can be called multipolarity. It was found that the narrower the ratio of aboveground mass to root mass, the better the conditions for generative develop- ment. Under unfavorable conditions, unipolarity is clearly observed (late August-early September). Plants weak after winter have a high dependence on spring weather condi- tions. In terms of mass, the root system of different sowing dates exceeded this indicator of plants of later dates many times, but in terms of depth, the difference was almost absent. Thus, plants of late sowing dates that appear weak in appearance have good potential for further development.Such late crops are usually much denser, because during germination in this case there is almost always no mois- ture deficit. In 2021, the spring was quite cool and warm- ing was gradual. In contrast, 2022 was characterized by average multi-year temperature trends, which were deter- mined by sharp warming with dry weather. This factor was crucial in shaping seed yields and individual plant producti- vity. Conclusions. Field germination and winter hardiness of winter rapeseed have minimal dependence on sowing dates. To a greater extent, these indicators are determined by the weather conditions of the autumn-spring period.The ratio of root and aboveground mass has a significant impact on the generative development of plants. The nar- rower the ratio of aboveground mass to root mass, the bet- ter the conditions for generative development. The yield of winter rapeseed seeds by sowing dates has a three-polar dimension. The optimum sowing dates were observed on July 25 (1.92 t/ha), August 25 (2.28 t/ha) and September 15 (2.12 t/ha). The maximum difference in seed yield in the year optimal for weather conditions between sowing dates did not exceed 29%.