Will Cereal Crops Better Cope with Climate Change in Agroforestry? A First Assessment with a Rain Reduction Experiment in a Mature Alley-Cropping System

International audience; Climate change is challenging the sustainability of European cropping systems. In many parts of Europe, less rainfall and higher temperatures are expected in the future, and will increase the water and thermal stresses that cereal crops face, especially during sensitive phenological stages such as germination, anthesis or grain filling. Agroforestry, and more specifically alley-cropping, is an agronomical practice that combines the production of aligned trees and crops on the same parcel. Such a system increasingly attracts farmers, is encouraged by the European Common Agriculture Policy, but is still unusual within the European landscape. In the context of climate change, the microclimate conditions in the understorey of agroforestry trees might help mitigating the adverse effects on crop productivity of more frequent climate hazards such as droughts or heatwaves. While this hypothesis is widely exposed in the literature, it was never evaluated experimentally in the field. The balance between the positive (facilitation through climate mitigation) and negative (competition for water, nutrients and light) effects of the trees on the crop is still undecided, and may be sitespecific or very dependent of the plot management scheme. A unique rainfall and temperature manipulation experiment has been set-up at the Restinclières Agroforestry Farm Estate, 15 km North of Montpellier (France). This is probably the first ever large scale trial on rainfall reduction in temperate agroforestry. We compare two cereal cropping systems: a standard treeless system and a mature alleycropping system with 22 year old hybrid walnut trees (92 trees.ha-1). In both systems, we designed a mobile rainfall capture system that allows to compare the natural rainfall pattern with a reduced rainfall pattern. When expanded during the night, the system also allows passive night warming of the plots. We monitored a winter barley crop from seeding in November 2017 to harvest in June 2018. The first results that will be presented include : 1) the description of the successful guyed prototype of mobile large scale rainfall capture system; 2) the comparison of the regime of rainfall and temperature achieved with the rainfall capture system with the reference standard weather; 3) the response of the barley crop to the standard and modified climates, in both treeless and agroforestry systems. A special emphasis will be put on the yield components and the physiological responses of barley. Thermal stresses during anthesis and grain filling will be documented by a close monitoring of the organ-level temperatures of the barley ears. The high level of climate protection and light competition secured by the tall (13 m height) walnut trees ensures that this experiment will document high levels of tree-crop interactions.