Long‐term crop yield benefits of subsurface drainage on poorly drained soils

Abstract Subsurface drainage is an important agricultural practice that has been widely utilized in the US Midwest to improve the productivity of poorly drained soils. Although widely adopted, long‐term yield benefits of drainage, particularly with varying spacings, in an ever‐changing climate are largely unknown. The goals of this study were to assess how various drainage spacings (5, 10, and 20 m) impacted crop yields compared to the undrained control in a long‐term trial (started in 1984) in southeastern Indiana and how these effects were influenced by the amount of rainfall of specific periods of the growing season. Drainage treatments led to an increase in corn ( Zea mays ) yields (by 12%–17%) but did not significantly affect soybean ( Glycine max ) yields compared to the control. In the initial 10 years of the experiment, drainage benefits were subtle and corn yields did not vary significantly across spacing treatments, whereas in the most recent 10 corn years, the drainage treatment effects became more pronounced, likely due to the combined effects of long‐term drainage system and conservation practices of no‐till and cover crops. Over 37 years, corn yields remained stagnant in the undrained plots but progressively increased in the drained treatments. Both corn and soybean yields showed a negative correlation with rainfall 14 days post‐planting, while drainage spacing treatments partially mitigated this negative effect. Our findings underscore the importance of effective drainage as a necessary prerequisite for realizing the potential benefits of conservation practices and improved crop genetics for increased crop productivity.