Agricultural Soil Science in a Changing Climate: Soil Health, Carbon Cycling, Nutrient Dynamics and Agroecosystem Resilience

Subsurface drainage is indispensable to crop production on many poorly drained soils, yet rapid removal of water can accelerate nutrient export and reduce the soil-water reserve available during subsequent dry periods. Controlled drainage (CD) and controlled drainage with subirrigation (CDSI) seek to convert a fixed drainage network into an actively managed water-table system. This critical narrative review integrates hydrodynamic modelling, field water-table management, agronomic response, and nitrogen and phosphorus mitigation. Literature was selected from agricultural, environmental and multidisciplinary scholarly sources, with emphasis on peer-reviewed field experiments, long-term syntheses, meta-analyses and process-based modelling studies. The evidence is strongest for a hydrologic mechanism: raising the effective outlet elevation commonly reduces subsurface drainage discharge and therefore nitrate load delivered through drain outlets. Concentration responses are less consistent, and field-scale outlet reductions cannot automatically be interpreted as whole-system nutrient removal because retained water may be redistributed to evapotranspiration, surface runoff, deep percolation or lateral seepage. Phosphorus responses are more equivocal than nitrate responses because dissolved and particulate pathways can shift in opposite directions as the water table is raised. Yield effects are similarly conditional; benefits are most plausible when stored or supplied water relieves seasonal water deficit, whereas excessive or poorly timed water-table elevation can increase waterlogging risk. DRAINMOD and its nutrient and crop extensions provide the most established field-scale framework, while HYDRUS-2D, RZWQM2, SWAT/SWAT+ and SWAP address complementary process or scaling questions. Model credibility depends on independent validation of water-table depth, flow, nutrient loads and crop outcomes, not calibration to outlet flow alone. The synthesis supports adaptive, site-specific operation rather than static high-water tables, and identifies catchment-scale water accounting, phosphorus pathway representation, automated control under forecast uncertainty, salinity constraints, and multi-objective field validation as priorities for future research.