Interactions between drought and shade on the productivity of winter pea grown in a 25-year-old walnut-based alley cropping system

In the face of climate change, more frequent drought events are expected in the Mediterranean regions. Alley cropping is an agroforestry practice that represents a promising adaptation strategy to sustain yield productivity under drier conditions. However, the presence of trees limits the productivity of the intercrop by reducing light availability and by competing for soil water resources, which could potentially exacerbate the yield losses due to drought conditions. Furthermore, the effects of co‐occurring drought and shade stresses on annual crops are still poorly understood. To tackle this issue, we performed a rainfall manipulation experiment on winter pea (Pisum sativum L.) grown in full‐sun conditions (agricultural control) and under different levels of shade in a 25‐year walnut‐based alley cropping system located in southern France. We evaluated first the effect of trees on light and water availability, and we then studied the effects of early drought (135 mm excluded from April to the end of May) and light conditions on crop performances and yield components. At 3.5 m from the tree line, light availability was reduced on average by 19% at south and 35% at north of trees over the entire crop cycle and mostly after tree budburst. The impact of trees on soil water content in the crop root zone was weak thanks to the good complementarity of the respective root systems. Under normal rainfall conditions, tree shade decreased pea yield from −25% to −77% compared to full‐sun conditions. In case of spring drought, pea yield was decreased by −22% in full‐sun conditions. The negative effect of tree shade was reduced and decreased pea yield only by −1% to −47%. Under the most intense shade conditions, pea yield was even higher under drought than in normal rainfall conditions. The analysis of crop dynamics and yield components revealed that the vegetative development of pea ceased under drought to the benefit of biomass allocation towards the reproductive organs. Pea yield was less impacted by tree shade under spring drought because yield elaboration relied less on the success of pod set, sensitive to shade and, more on grain filling, improved in case of early drought event. This study supports the hypothesis that agroforestry systems may be more resilient in the case of early drought.