Application of a robust experimental method to study soil warming effects on oilseed rape

Climate change is expected to cause a mean annual temperature increase in Germany of up to 4 °C by 2100. Hence, field manipulation experiments for the assessment of the impact of global warming on agricultural production are needed to supplement existing modeling approaches. Here, we present a soil warming facility adapted for field crops, enabling common agronomic practices, including soil tillage, to be carried out while simulating natural warming scenarios. The experimental setup consists of buried heating cables and a fully computerized temperature control and data logging system. Treatments reflected medium- (up to 2050) and long-term (up to 2100) climate warming scenarios compared to the unheated (ambient) control. In a year-round experiment, there were no technical problems and the programmed temperature offset was kept stable at two levels, +1.6 °C (±0.17 °C) or +3.2 °C (±0.27 °C) above ambient throughout the experiment. We assessed warming effects on the plot microclimate as well as on biological parameters in a winter oilseed rape crop (Brassica napus L.). Growth stages were advanced in October and April, and plant length before flowering was significantly higher in the warmest treatment compared to the unheated control plots. Overall, our method proved stable and reliable under field conditions enabling common agronomic practices to be carried out while observing the effects of increased soil temperatures.