Controlled Drainage – An Important Practice to Protect Water Quality That Can Enhance Crop Yields
Agricultural drainage systems are widely used in North Carolina to increase crop yield and improve the year-to-year consistency of production. Drainage systems provide trafficable conditions for timely planting, harvesting, and other field operations, and the systems remove excess water from the root zone to alleviate crop stress that occurs when soils are saturated for extended periods. Drainage improvement can be accomplished through surface drainage (land grading to remove excess surface water following large storm events) and subsurface drainage (ditches or drainpipes that remove excess water from the soil profile).
The most economical way to improve subsurface drainage is to install ditches or subsurface drains as deep and spaced as wide as possible to satisfy production requirements. Typical subsurface drainpipe depths in eastern North Carolina range from 3 to 5 feet, and the pipes are often spaced between 50 to 200 feet apart. Ditches are typically the same depth but are spaced from 150 to 600 feet apart depending on the intensity of surface drainage. These design parameters are typically determined based on outlet conditions, soil types, topography, crop tolerance to wet conditions, and economics. From a farming perspective, the producer's goal is to install a well-designed drainage system that will result in the highest crop yields with the minimum investment possible. However, drainage requirements vary widely for the same farm from year to year and within the same year, depending on weather conditions, cropping system, and farming practices. Therefore, even the best designed systems may overdrain the field (meaning lowering the water table too far below the root zone) during intermittent wet and dry growing periods, causing deficit water stress on crops and increased water and nutrients loss from the farm.