Agroecological determinants of rapeseed yield variation

Global food and energy security largely depends on the rate of main crops yield increase, so the research of limiting factors of yields is a pressing issue today. The aim of this work was to determine the contribution of agro-ecological factors, namely, bioclimatic variables, soil indicators and factors of landscape diversity to the variation of rapeseed yield parameters on the territory of Polissya and Forest-steppe zones of Ukraine during 1991–2017. The average rapeseed yield data by the administrative district for 10 regions was used as the material. The dynamics of rapeseed yield from the mid-1990s to the present described by a log-logistic model. The parameters of the yield model are the following indicators: lower limit of yield; upper limit of yield; slope that showing the rate of change in yield over time and ED50 – the time it takes to achieve half of the maximum yield level. There are statistically significant regression dependencies between rapeseed yield parameters and agroecological factors (p <0.05). Rapeseed yield parameters of 43‒68% are due to the action of agri-environmental factors, which determines this crop as sensitive to environmental changes. Agroecological factors by 43‒68% determine the variability of rapeseed yield, which determines this crop as sensitive to environmental conditions. The most sensitive to agroecological factors is the upper yield limit. There is a correlation between the Shannon index and the slope of the rapeseed yield regression model, as well as between the distance to the objects of Natural Reserve Fund (NRF) and the upper limit of yield. ED50 and the landscape diversity index are quadratically correlated, indicating the complex nature of the relationship between this yield parameter and landscape diversity. Rapeseed productivity is mostly influenced by the continentality of climate among other climate variables. High sensitivity of rapeseed yield parameters to soil indices was found, and mostly to the soil structure (sand content in soil), which largely determines the rapeseed yield spatial variation. The aspects of rapeseed yield variation that we have identified are quite important both in terms of forecasting models and in terms of farmland management.