Restrictive irrigation improves yield and reduces risk for faba bean across the Middle East and North Africa: A modeling study

CONTEXT: Faba bean is a crucial component of Mediterranean food systems. However, the crop is somewhat underrepresented in the major crop models and usage of these models requires substantial calibration with data that might not be available. The Simple Simulation Model (SSM) is a simple, non-calibrated and physiology based model that has the advantage of having a reduced number of parameters that can all be measured or inferred from simple experiments. OBJECTIVE: We aimed to parameterize and assess the capacity of the SSM to simulate faba bean phenology, dry matter accumulation, nitrogen accumulation and final yield and to explore the impact of supplemental irrigation on crop production. MATERIALS & METHODS: Model simulations were compared to observations collected over 30 experimental situations in Morocco, Tunisia, and Lebanon. SSM was then used to explore water restrictive irrigation scenarios, allowing two irrigation events after flowering, with a total irrigation dose of 50 mm, in the Middle East and in North Africa (MENA). RESULTS AND CONCLUSIONS: The prediction error on final total above ground dry matter was satisfactory and the dynamics of dry matter and nitrogen accumulation in plant organs matched the observations. This study showed that 50 mm irrigation can be sufficient to substantially improve faba bean production sustainability in MENA. In the driest areas (below 200 mm in-season rainfall), 50 mm irrigation could reduce the risk of low crops by up to 34% and increase yield sufficiently to meet average farm household needs. In more humid areas of the region, 50 mm irrigation could improve faba bean yield by up to 1 t/ha compared to an average yield of 3.5 t/ha. Simulation outputs showed that deficit irrigation could improve N soil balance and soil health in the mid-to long-term. The analysis of the simulation results can be used to advise farmers on best adapted irrigation dates without additional in situ measurement. SIGNIFICANCE: This study revealed that non-calibrated models such as SSM can simulate yield and dry matter accumulation with a predictive capacity similar to calibrated tools making it suitable for addressing a known gap in irrigation management for Mediterranean food systems. In the MENA region, relative small amounts of irrigation (50 mm) can substantially reduce production risk, and so increase security for farmers, and improve faba bean productivity and sustainability.