The spatial patterns of long-term temporal trends in yields of soybean (Glycine max (L.) Merril) in the Central European Mixed Forests (Polissya) and East European Forest Steppe ecoregions within Ukraine

This research aimed to characterize the spatial and temporal yields trend of soybeans in 267 administrative districts in Polissya and Forest-steppe ecoregions within Ukraine over 27 years (1991 – 2017). The common feature of temporal changes for all administrative districts is the existence of the trend that can be described by the fourth- degree polynomial. The trend type indicates its agro-economic (agro-technological) origin. Soybean yield dynamics can be described and interpreted by characteristic points of the fourth-degree polynomial. The absolute term of polynomial equation indicates the productivity of the soybean in the starting period. This indicator enables identifying areas with the most favorable soil conditions for soybeans cultivation. It is more appropriate to grow soybeans in the forest-steppe zone of Ukraine, and less appropriate in Polissya. The indicators of the maximum rate of reduction and the maximum rate of increase of yields can be used as markers of agroecosystem stability to agro-economic agro-technological factors. The value of the coefficient of determination indicates the contribution of agro-technological and agro-economic factors in soybean yields variation. These factors determine 7 – 89% of soybean yield depending on the area. The soybean yields in southern and eastern areas of the research region are the most sensitive to agro-technological and agro-economic factors and yields in the northern and western areas are the least sensitive.