What Is Controlled Drainage And Subirrigation?

Published online: May 03, 2023 Articles Soils Matter, Get The Scoop
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One of the most important jobs for a grower is managing water. Some areas of the United States have plenty of rainfall throughout the growing season. Others do not. And still others have too much water at some times of the year and not enough water at others. All of these different farm fields need different water management systems.

Navdeep Singh and Gabriel T. LaHue, who work in the Department of Crop and Soil Sciences at Washington State University, focus on solutions for growers whose fields experience dry periods during the growing season. They already have drain tiles installed under the field – which were put in for wet seasons. This is important because limited soil moisture can reduce crop yield, especially if water is limited during key plant growth stages. The team is working on systems that can respond to varying rainfall patterns during the growing season:

  • removing excess water from field;
  • conserving existing soil moisture; and,
  • pumping supplemental water into the field to raise water table.

This controlled drainage system can store water under the root zone – which allows plants to get the oxygen they need, while simultaneously conserving water for when an area experiences a dry period during the growing season. Think of it like a large rain barrel – under the farmland.

Growers need to install a “water level control structure” at the outlet of the tile drains. This structure has adjustable riser boards that can be used to control how much water drains from the farm. For instance, during early spring and in the fall, the riser boards can be removed from the system. The roots can get oxygen – and it helps the fields dry enough to allow farm equipment to be used for planting. During the growing season, riser boards can be raised to reduce drainage and store more water in the soil for crop use.

These systems can both drain excess water – and store it underground when needed. They need to be managed throughout the year depending on the distribution of rainfall within the growing season.

Controlled drainage can be expanded upon to include subirrigation. Irrigation water from external water sources (e.g., surface water or groundwater wells) is pumped into the system. It can then flow back through the drain tiles into the field. This raises the water table to meet the crop water requirements.

Farm fields that best fit with this model are:

  • flat fields with poor natural drainage
  • fields with the presence of restrictive layer beneath the crop root zone,
  • fields that have relatively rapid lateral flow of water in the subsoil,
  • and adequate external water supply.

How well these systems work will depend on soil texture and the amount of rainfall during the growing season. Farms with medium-textured soils (loam, silt loam, etc.) and regions that receive less rainfall during the growing season will benefit the most. Efficient management of these controlled drainage systems is important to harness their many potential benefits.

Answered by Navdeep Singh and Gabriel T. LaHue, Department of Crop and Soil Sciences, Washington State University