Developing stage-specific drought vulnerability curves for maize: The case study of the Po River basin

Drought and water stress negatively affect many human activities, with agriculture playing a crucial role in ensuring food security. The drought vulnerability assessment of agricultural systems has been widely investigated in the past and the relationship between drought hazard and losses has been traditionally expressed through vulnerability curves. This study develops maize drought vulnerability curves tailored to the context of the Po River Basin (Northern Italy) which is the largest Italian agricultural area and accounts for 35% of national crop production. The curves express the relationship between crop water stress and maize yield losses. Four crop growth stages are considered (establishment, vegetative, flowering and yield formation) since the sensitivity of maize to water stress is strictly related with the plant growth stage. In addition, the influence of soil texture on the maize response to water stress is investigated. The Agricultural Production System sIMulator (APSIM) is used to simulate the crop yield and the water stress. APSIM is calibrated on observed yield and the model skill in reproducing maize yield is satisfactorily verified (Pearson correlation coefficient equals to 0.87). Flowering is the most sensitive stage to water deficit independently from the soil texture, while the yield formation phase is most sensitive to water stress than the vegetative in the case of Loam soils. The achieved results suggest the importance of the use of appropriate irrigation strategies. Water should be provided to maize in case of a water stress during the flowering phase to avoid irreparable yield losses.