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Sub Irrigation

Sub Irrigation allows you complete control over your water table. This is done by raising/lowering your outlet depth and pumping water for irrigation into the tile lines.


Sub-irrigation (SI) is irrigating your crops using a new or existing tile drainage system. The sub-irrigation system is designed to drain your field when excessive moisture is present and add water to the soil profile when the soil begins to dry out and crops need the water for maximum productivity. An existing tile system may need to be modified for maximum water management efficiency and the highest yield potential.

SI 1

Diagram showing how a standard SI system works. Water enters the tile through an external water source. The water then flows through different management zones being controlled by watergates and control structures

Sub-irrigation is used in conjunction with drainage water management. It improves water quality by decreasing drainage water volume, therefore reducing fertilizer and nutrient loss to streams by as much as 30 to 50%, while maximizing the use of subsurface water resources. Structures for water control hold the water in the soil profile as long as it’s needed. By controlling the water elevation in that structure, you can drain off any excess water that’s no longer needed. This whole system can be automated to drain when needed and add water to the profile through a software program managed from an office or shop on the farm.

SI graph


Sub-irrigation reduces crop stress during dry periods by adding water through your drainage system. Subsurface irrigation provides a more efficient option for delivering water to your crops root system, improving plant health, and has been shown to increase yields by as much as 64%. It has been shown to use one half the amount of water and one third the energy to provide adequate water to the crops when compared to other irrigation systems. Sub-irrigation is effective where the topography is nearly flat; the soils are suitable to hold the water table at the correct level; where a water source is available; and the tile system is properly designed for sub-irrigation.



The Golden Rule of Drainage: “Drain only the amount of water needed to ensure
equipment access and healthy crop production, and not a drop more.”
–R. Wayne Skaggs, North Carolina State University


For more information on Sub Irrigation, contact our Lead Conservation Planner.
Email Andy Mackrill; andy@ecoexch.com