Winter wheat is the main grain crop in Ukraine, but in recent years its yields have been declining and grain quality has been deteriorating. A significant amount of winter wheat grain does not meet the requirements for food grain, which in turn affects the quality of flour and bread. The main factor for obtaining highly productive winter wheat crops is to improve their structure, which depends on the sowing time, seeding rate, field germination of seeds, plant survival in winter, etc. The yield and quality of winter wheat seeds are formed during the period of their cultivation, where both the genetic potential of the variety and soil, climatic and agronomic conditions play an important role [4]. Therefore, creating favourable conditions for high field germination of seeds is one of the priority tasks in growing grain crops.
The aim of the study is to determine the influence of weather factors on the field germination of winter wheat seeds.
The research programme envisages determining the impact of weather conditions - average daily temperatures, the sum of active temperatures, precipitation during sowing and germination, and productive soil moisture reserves at a depth of 0-10 cm - on the field germination of winter wheat seeds. Laboratory and field studies were conducted at the experimental farm of the Institute of Plant Physiology and Genetics during 2016-2020. Varieties of different maturity groups - medium early and medium early - were used for the study. Field germination was calculated as the ratio of the number of seedlings to the total number of sown germinating seeds.
Studies of the influence of weather conditions on the field germination of winter wheat seeds have shown that in 2016 the temperature regime of this period was lower, the sum of active temperatures was 117,5 ºC, the average daily temperature was 11,8 ºC, and the amount of precipitation for three decades was only 5,4 mm, with a moisture deficit of 88,0%. Such conditions did not contribute to the accumulation of productive soil moisture and its preservation, which led to a decrease in the percentage of field germination of seeds to 76%.
With a high sum of active temperatures during the third decade of September 2017 of 141,1 oC and 2,2 mm less precipitation in September, the productive moisture content of the sowing soil layer (0-10 cm) was 23 mm, which is below the optimal level (30 mm), and the average field germination rate of the varieties' seeds was 77%. The period of sowing and germination in 2018 was characterised by sufficient moisture supply, with precipitation at the level of the long-term average of 57,7 mm (36,5 mm in the first decade and 21,2 mm in September), which was 28,2% higher than the long-term average, and productive soil moisture of 34 mm, which ensured field germination at 82%.
The periods of sowing and germination in 2019 and 2020 were also favourable for seed germination. The average daily air temperature, which was at the level of the long-term average in 2019 and 2,8 °C higher than the long-term average in 2020, and sufficient precipitation, which contributed to the accumulation of productive moisture in the soil (37 mm in 2019 and 35 mm in 2020, which is 7-5 mm more than optimal), ensured field germination of seeds at the level of 86% and 83%, respectively.
The study of the influence of varietal characteristics on the field germination of seeds revealed that with almost the same laboratory germination of sown seeds, there was no significant difference between varieties in field germination of both medium early and medium early varieties.
On average, for medium-early ripening varieties, the field germination of seeds over five years was 81% with variation by variety from 80 to 82%, and for medium-ripening varieties also 81% with variation by variety from 80 to 83%. Over the years of research, there was also no significant difference in field germination of seeds depending on varietal characteristics, it changed only depending on weather conditions during sowing and germination.
