Analysis of soybean germination, emergence, and prediction of a possible northward establishment of the crop under climate change

Soybean (Glycine max (L.) Merr.) has the potential to improve sustainability of agricultural production systems. A higher focus on this crop is needed to re-launch its production in the EU. A better understanding of key determinants affecting soybean establishment represents a first step to facilitate its adoption in cropping systems. To this objective, we conducted laboratory and field experiments in order to better characterize seed germination and seedling growth in relation to temperatures, water content, and soil structure. We then used these data to parametrize the SIMPLE crop emergence model and to evaluate its prediction quality, by comparing observed field germination and emergence data with the predicted ones. Finally, we performed a simulation study over the 2020-2100 period, for three sowing dates, from mid-March to mid-April, in the northern climate of France to evaluate whether soybean will successfully establish in the Northern part of the country under future climate change. Experimental results showed that soybean germination was very fast, taking only 17 degrees C days to reach 50% germination at optimal conditions. The base, optimum and maximum temperatures were determined as 4, 30 and 40 degrees C, respectively while the base water potential was - 0.67 MPa, indicating a high sensitivity to water stress. The SIMPLE model finely predicted germination and emergence courses and their final rates, compared with the observed field data. The simulation study showed average emergence rate ranging from 61 to 78% with little variability among sowing dates and periods, but a high variability between years. Main causes of non-emergence were: i) seedling mortality due to clods or soil surface crust, followed by ii) non-germination, and iii) seedling mortality due to drought. When sown in mid-April, seedling mortality due to drought was higher compared with earlier sowing dates. These results provide a better knowledge of soybean establishment that are encouraging to introduce soybean with early sowings to diversify current cropping systems.