Salinity management with subsurface drainage over 9 years in a soybean–wheat–corn rotation

Soil salinity is a global issue that impacts crop production and requires management to contain and ameliorate. Although field-scale assessments are limited, a recent strategy used to manage salinity in the Northern Great Plains is the wide-spread adoption of subsurface drainage. Therefore, a study was conducted between 2013 and 2021 on a 57-ha field in southeastern North Dakota where changes in soil salinity, groundwater quality, and grain yields (soybean [Glycine max], wheat [Triticum aestivum], and corn [Zea mays L]) were compared between subsurface tile drained (TD) and undrained (UD) areas at the field scale. Topsoil (0–15 cm) electrical conductivity of saturated paste extract (EC_e) decreased at a rate of 0.15 dS m⁻¹ year⁻¹ for TD but increased 0.03 dS m⁻¹ year⁻¹ for UD. The groundwater electrical conductivity of water (EC_w) decreased 0.5 and 0.3 dS m⁻¹ year⁻¹ for TD and UD, respectively. Soil EC_e, chloride (Cl⁻), sulfate-sulfur (SO₄²⁻-S), calcium (Ca²⁺), sodium (Na⁺), and magnesium (Mg²⁺) concentrations increased with soil depth for TD and UD. However, these ion concentrations decreased with time for TD and stayed relatively unchanged or increased for UD. Groundwater EC_w and ion concentrations decreased over time for TD and to a lesser extent for UD. Groundwater levels increased slightly for TD but increased more for UD, where high water tables caused wet soil conditions resulting in yield reduction in several years. Soybean yields increase by 0.18 and 0.06 Mg ha⁻¹ year⁻¹ for TD and UD, respectively. Wheat grain yield increased over time for TD and UD at similar rates (0.17 and 0.18 Mg ha⁻¹ year⁻¹, respectively). Corn grain yield increased slightly from 2016 to 2019 for TD, but decreased by 6.2 Mg ha⁻¹ from 2016 to 2019 for UD due to wet soil conditions. Overall, the outcomes of this field-scale study provide validation of similar outcomes reported in small-scale studies for subsurface drainage as a management tool for soil salinity in the Northern Great Plains.