Duration of interphase and growing periods of soybean varieties depending on hydrothermal conditions and application of soil and post-emergence herbicides

The purpose of the research was to determine the duration of the interphase and growing periods of soybean varieties depending on the use of soil and post-emergence herbicides. The research was conducted in 2021- 2023 in the conditions of LLC «Savarske» Obukhiv district, Kyiv region. Experiment scheme: Factor A. Varieties of soybeans. 1. «Aurelina»; 2. ES «Commandоr»; 3. ES «Navigator». Factor B. Herbicides. 1. Control (water treatment); 2. «Primekstra TZ Gold» 500 k. s. (4.5 l/ha), before crop seedlings emergence; 3. «Frontier Optima» (1.2 l/ha) + «Stomp» 330 (5 l/ha), before crop seedlings emergence; 4. «Bazagran» (3 l/ha) + «Fusilade Forte 150 ES» (1 l/ha) in the phase of 4-5 leaves of the crop; 5. «Korum» (2 l/ha) + «Achiba» (2 l/ha), in the phase of 2-4 leaves of the crop. The total area of the elementary plot is 144 m2 ; the registration plot is 120 m2 . The experiment was repeated three times. According to the observations, it was found that in 2021 the weather conditions were favorable for the growth, development and formation of soybean productivity. Precipitation amount during the growing season was 324.1 mm; the average air temperature was 17.8°C. In 2023 these figures were 275.9 mm and 18.0°C. In 2022, due to dry conditions, precipitation amount did not exceed 240.2 mm and the average air temperature was 17.2°C. The hydrothermal coefficient (HTC) in May 2021 was 2.7, and in 2022 and 2023 it was 0.5. High temperatures and decreased precipitation in June 2022 led to a decrease of the hydrothermal coefficient to 0.4. The weather conditions in June 2021 and 2023 resulted in a HEC of 0.7 and 0.8. July 2021 and 2023 were excessively wet in terms of the HCC, and in 2022 there was a slight drought. September 2021 was quite dry (0.4) and in 2022, on the contrary, it was too wet (2.8). The biggest growing season length was for the early maturing soybean variety «Aurelina» (106-109 days) and 97-99 and 99-101 days for the very early maturing varieties «ES Commander» and «ES Navigator». In the variants of herbicide application the duration of the growing season was 2-3 days shorter compared to the control plots. There were no differences in the duration of interphase or growing season between the varieties using soil or post-emergence herbicides. The herbicides effect was the greatest on the change in the duration of the «interphase flowering period to full grain maturity» (BBCH 66-87). Soybean vegetation duration has an average connection with precipitation (r = 0.73), air temperature (r = 0.62) and strong feedback with the hydrothermal coefficient (HTC) (r = -0.90).