Aubertot, J.-N. | bioRxiv Science

bioRxiv2019

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

Soybean (Glycine max (L.) Merr.) has 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 future climate change will help expand soybean from Southern to Northern part of the country. Soybean germination was very fast, taking only 15 {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 -0.7 MPa, indicating a high sensitivity to water stress. The SIMPLE model well-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 seedling mortality due to clods or soil surface crust followed by non-germination and seedling mortality due to drought, especially for mid-April sowing. These results provide a better knowledge of soybean establishment that are encouraging to introduce soybean with early sowings to diversify current cropping systems.

plant biology↗

bioRxiv2019

Will climate change affect sugar beet establishment of the 21st century? Insights from a simulation study using a crop emergence model

Ongoing climate change has been reported to have far-reaching impact on crop development and yield in many regions of the globe including Europe. However, little is known about the potential impact of climate change on specific stages of the crop cycle including crop establishment, although it is a crucial stage of the annual crop cycles. For the first time, we performed a simulation study to pinpoint how sugar beet sowing conditions of the next eight decades will be altered under future climate change and if these variations will affect sowing dates, germination and emergence as well as bolting rates of this crop. We chose Northern France as an important study site, representative of sugar beet growing basin in Northern Europe. Sugar beet emergence simulations were performed for a period between 2020 and 2100, taking into account five sowing dates (mid-February, 1st March, mid-March, 1st April and mid-April). Soil water contents and temperatures in the 0-10 cm soil horizon were first simulated with the STICS soil-crop model using the most pessimistic IPCC scenario (RCP 8.5) to feed the SIMPLE crop emergence model. We also evaluated the probability of field access for the earlier sowings, based on the amount of cumulated rainfall during February and March. When analyzed by sowing date and for successive 20-year period from 2020 to 2100, there was a significant increase in seedbed temperatures by 2{degrees}C after 2060 while no change in cumulative rainfall was found before and after sowings, compared with the past. Emergence rate was generally higher for 2081-2100, while time to reach the maximum emergence rate decreased by about one week, compared with other periods, due to higher average seedbed temperatures. The rate of non-germinated seeds decreased, especially for the earlier sowing dates, but the frequency of non-emergence due to water stress increased after 2060 for all sowing dates, including the mid-February sowing. Bolting remains a risk for sowings before mid-March although this risk will be markedly decreased after 2060. The changes in seedbed conditions will be significant after 2060 in terms of temperatures. However, the possibility of field access will be a main limiting factor for earlier sowings, as no significant changes in cumulative rainfall, compared with the past, will occur under future climate change. When field access is not a constraint, an anticipation of the sowing date, compared to the currently practiced sowing (i.e. mid-March), will lead to decreased risks for the sugar beet crop establishment and bolting. The use of future climate scenarios coupled with a crop model allows a precise insight into the future sowing conditions, and provide helpful information to better project future farming systems.

plant biology↗