Evaluation weather conditions for growing sunflower (Helianthus annuus L.) in the northern part of the Left-bank Forest Steppe of Ukraine

Pourpose. Establish compliance of heat and moisture resources to biological requirements of sunflower hybrids (Helianthus annuus), reveal criteria for assessing weather conditions in the northern regions of Ukraine; establish links between temperature, precipitation and yield. Methods. Field and mathematical methods were used. Field multifactorial experiment was conducted during 2016–2018 in the Left Bank of Ukraine, on the border of two soil and climatic zones of Ukraine - Forest-Steppe and Polissya. Peculiarities of plant growth and development, formation of "hybrids" yield (factor A) were studied: 'Ukrainskyi F1', 'P63LL06', 'NK Brio', 'NK Ferti' depending on "plant density" (factor B): 50, 55 , 60, 65 thousand pieces/hectare. We calculated and analyzed the sums of active, effective temperatures for two biological minima - 5 and 10 ° C; the sum of thermal units according to the method of Brown and Bootsma, 1993; coefficients of materiality of elements deviations of the agrometeorological mode of the current year from long-term averages; plasticity and yield stability according to the method of Eberthart S.A., Russel W.Q. (1966). Results. To pass the full cycle of sunflower plants development, the sum of active temperatures (t = 10 °C) for hybrid 'Ukrainskyi F1' – 2354.6; P63LL06 – 2306.4; 'NK Brio' – 2401.3; 'NK Ferti' – 2379.7; and the sum of effective temperatures for 'Ukrainskyi F1'- 1081.5; 'P63LL06' – 1056.9; 'NK Brio' – 1104.9; 'NK Ferti' – 1109.1 is required. The sum of temperatures, both at a biological minimum temperature 10 °C and 5 °C, meet biological needs of sunflower plants and is not a limiting factor for this crop growing. The sum of thermal units for the period April–October is 3780 on average for three years. During the period of active sunflower vegetation (April–August) the sum of thermal units is 2868–3258, significantly exceeding the sum of active and effective temperatures at biologically active temperatures 5 °С and 10 °С. The most determined limits of changes in active, effective temperatures and thermal units were observed in May – September. Conclusions. Plasticity and stability of sunflower yield more depending on hybrid and plants density than on conditions of the year. Yield stability coefficient for hybrid 'Ukrainskyi F1' was 1.68 - 2.30; 'P63LL06'- 2.51 - 3.14; 'NK Brio'- 3.15 - 4.63; 'NK Ferti' - 2.70 - 3.75 for yields, respectively: 2.16 - 3.11; 2.58 - 3.52; 3.20 - 4.12; 2.70 - 3.79 t/ha.