Effect of increasing conceptual model detail on simulated crop yield-drainage base relations

The relation between the drainage base (the maximum depth to which water is drained) and crop yield is important for designing drainage systems or deriving practical drainage standards. For integrated regional water management in temperate climates, a shallower drainage base is seen as a suitable measure to cope with prolonged periods of drought. This study aims to evaluate the effect of increasing level of conceptual model detail, that was the result of drainage science developments in the last decades, on the relation between crop yield and drainage base on field scale. We simulated potential and water-limited fodder maize yields for a fictional field with a sandy soil between 1925 and 2024 under Dutch meteorological conditions, using standard parametrisations for different subroutines available in the SWAP model for the simulation of potential evapotranspiration, crop growth and oxygen and drought stress. Each of these subroutines differ in level of conceptual detail and incorporated process-based knowledge. Results show that the relation between relative yield and the drainage base changes with varying level of detail, also when other crop types, sandy soils, bottom boundary condition configurations, and drainage resistances were used. The definition of a minimum relative yield for regional water management becomes more important as simulation results indicate an increasing influence of oxygen and drought stress on crop growth between different progressive climatic periods. Such a minimum relative yield would allow for relaxation of the currently used uniform Dutch guidelines for drainage design necessary for the transition in Dutch regional water management. • The level of model detail influences simulated yields for a certain drainage base. • Oxygen and drought stress impacts on crop growth increased over the last century. • Defining an acceptable minimum relative yield is key for regional water management. • That would permit deviation from current uniform Dutch drainage design rules.