Effect of soybean cultivars sowing dates on seed yield and its correlation with yield parameters

Circa over the recent dozen years, there has been observed some interest in soybean cultivation at a larger scale in Central and Eastern Europe, especially in the Danube region, the area most favourable to soybean growing in Europe (Dima 2016).In that relatively new soybean region, the research is necessary to determine the effect of environmental variation and cultivation technology, especially the date of sowing, on soybean growth, development and yielding.However, only four countries, Italy, France, Romania and Serbia, record continuously growing seed yields (Bastidas et al. 2008), and it is estimated that even 20% (of about 2.4 million ha) of the soybean imports can be replaced by its cultivation in Eastern Europe.One of the most important soybean cultivation conditions is the earliness of the cultivars grown as plant development, and ripening is closely related to the day length.It is commonly believed that in Europe, it is possible to grow soybean wherever the growing season is 105-140 days long, namely the cultivars with 000, 00 and 0 earliness, which means that the total temperature required for the growing season should range from 1 500 °C to 1 800 °C (Berschneider 2016).The key soybean plantations in Europe are found at 47-48° of north latitude (Miladinovic et al. 2006), while Poland is located at 49°00'N to 54°50'N.The analysis of the changes in weather parameters in Poland points to the shortening of the active soybean growth, prolonging the time the soil heats up to 8 °C at a depth of 5 cm, and to the occurrence of weather and agricultural droughts as well as latespring ground frosts (Zarski et al. 2019).The optimal soybean sowing date is an important factor affecting the plant growth and yield, and it changes depending on the climate conditions and the accompanying reactions of cultivars to the day length (Bastidas et al. 2008, Sincik et al. 2011).