Modelling the response of wheat yield to stage-specific water stress in the Po Plain

Droughts and water scarcity represent crucial issues for the agricultural sector, whose water demand is expected to increase in the next years to ensure food production for a growing population without expanding harvested areas. A proper assessment of crop water needs during the various plant growth periods provides useful information to effectively allocate water resources, highlighting the most drought-sensitive phenological stages. Winter wheat is the most widely grown cereal in the world. In Italy, it is mainly cultivated in the Po Plain, where the most severe drought of the last seventy years occurred in the summer of 2022. This work develops winter wheat drought vulnerability curves tailored to the Po Plain. The curves establish a relationship between water deficit and yield losses during various crop growth stages (establishment, vegetative, flowering and yield formation) and combinations of consecutive phases. Prediction bounds have been associated to vulnerability curves to assess the range of variation of the wheat response to water deficit. The effect of soil texture on wheat tolerance to droughts leading to water stress was investigated too. Results show that the flowering phase and the combinations including this growth stage are more sensitive to water stress with respect to the other considered phenological phases. In addition, winter wheat cultivated over clay loam soil is less sensitive to water deficit in comparison to the same crop grown on the other soil types considered in the study. The developed curves could be used in the framework of parametric insurance programs to pay indemnities based on the crop phenological stage and the soil texture. Moreover, the curves might be useful for land reclamation consortia, who could exploit them to schedule water delivery to farmers during drought or could be embedded into a drought early warning system to provide forecasts of crop yield losses in relation to the weather conditions.