Kris Kohl, Ag Engineering Specialist
Farm drainage with subirrigation is a comprehensive agricultural water management approach that involves both removing excess water from fields through drainage and, simultaneously, supplying water to the crop roots through subirrigation. This integrated system aims to optimize soil moisture levels, improve drainage, and enhance crop yields. What follows is a breakdown of the key components and benefits.
Farm Drainage
Tile drainage is the installation of a network of underground pipes or tiles to drain excess water from the soil. These drainage systems help prevent waterlogging, improve soil aeration, and create optimal conditions for root growth.
Benefits of Drainage:

• Improved soil structure and aeration.
• Prevention of waterlogging, which can harm plant roots. Corn grows until tasseling and doesn’t grow any more so if the soil gets waterlogged after that, the crop will suffer.
• Increased nutrient availability and uptake.
• Earlier planting and harvesting opportunities.
  Subirrigation
  Subsurface irrigation (Subirrigation) is supplying water to the crop roots below the soil surface. The tiles work in reverse with water being pumped out of the drainage ditch back into the field tile.
  Benefits of Subirrigation:
• Efficient water use, as it minimizes evaporation and runoff.
• Improved nutrient management, as water is delivered directly to the root zone.
• Water conservation, especially in areas with limited water resources.
  Integrated System
  Water control structures, such as gates, valves and pumps are used to control the water levels in the drainage and subirrigation systems. This allows for the adjustment of waterflow based on crop needs and weather conditions. The tile laterals need to be placed parallel to any slope and at low grade so that small changes in the control system will allow water to flow up the tile lines.
  Careful management to prevent nutrient runoff and protect water quality is necessary. Consideration must also be given to the ecological impact on nearby water bodies and ecosystems. Challenges include:
• The initial investment. Installation of drainage and subirrigation systems may require a significant upfront investment. A new system may be around $1,000 an acre for a complete system with pumps, head control and design. Older tile systems often maximized the lateral grade to minimize the amount of tile in a field.
• Maintenance. Regular maintenance is necessary to ensure the proper functioning of drainage and irrigation components. The head control systems require adjustment if you need to switch between drainage and subirrigation. Heavy rains in the summer are a blessing, but the pump needs to then be shut off.
• Site-specific considerations. The effectiveness of these systems depends on factors such as soil type and topography.
  Farm drainage with subirrigation is particularly beneficial in areas prone to both waterlogging and drought, as it provides a balanced approach to water management. It can contribute to sustainable agriculture by improving crop productivity while conserving water resources.
  Contact ISU Extension and Outreach Ag Engineering Specialist Kris Kohl at 712-732-5056 or kkohl1@iastate.edu for assistance with your Northwest Iowa farm.