Inside Drainage Water Management
Managing water resources is demanding more attention from farmers. The most commonly publicized concerns are related to supply and demand for irrigation water. But drainage water probably impacts even more farmers and acreage.
Drainage of excess water has been a key factor in U.S. crop production for over 100 years. Much of the tall-grass prairie of the Central and Eastern Corn Belt was unusable swamp land before surface ditches and subsurface tile drainage lines were installed. Millions of acres of our most productive cropland could not be farmed without the use of tile drainage systems to remove excess rainwater. Large areas that were partially drained 50 to 100 years ago are getting new systems installed to more effectively and more rapidly remove excess water.
Where drainage tile was previously installed to drain only the low spots, new grid systems are being installed to uniformly drain entire fields. Parallel lateral lines are being spaced closer together for quicker, more efficient drainage. Older full-field grids were typically installed with laterals spaced 100 to 120 feet apart. New systems commonly have laterals spaced 50 to 60 feet apart, or less.
Unfortunately, these systems work 24/7 — and continue to remove water even when the danger of crop loss is past.
Drainage Water Management (DWM) provides tools and practices to help farmers make more efficient use of their water resources two ways: By allowing drainage to facilitate field activities or protect the crop from excess water; And allowing the water level in the soil to be raised to support the growing crop.
Control structures (see above) installed in the drain lines at the edge of the field are used to adjust the water level in the field up or down as desired, preserving the water resources available to the crop and reducing the loss of nutrients that are also removed with the tile drainage. These nutrients are lost from benefitting the crop, and also pose a potential threat to water quality in the streams, rivers and other water bodies downstream. Nitrate loss can be reduced by 45% or more using DMW systems. Yet only about 1,000 DWM structures have been installed on U.S. farms up to now.
DWM control structures can be adjusted to freely drain water from the field in the spring to allow for field work. The gates, or stop-logs, are then closed after planting to hold back water loss. During the growing season, the water level is adjusted downward to support deeper root penetration as roots move down the soil profile. In the fall, the gates are again removed for harvest and other fall field work. They can then be closed to hold water during the winter months.
Of course, heavy rainfall at any time may result in the need to release water to prevent flooding. The DWM stop-logs can be adjusted as needed. It usually takes only a few hours to lower the field’s water level with a properly designed system. Each DWM structure can usually control the water level for 20 to 30 acres.
Newer technology allows the control structure gates to be operated electronically and powered by solar cells, with radio or internet control. The operator can monitor the system and adjust water levels from a computer or cell phone. If farmers work cooperatively, it may soon be possible to network these systems to manage water levels throughout a watershed. Operating DWM systems might someday become a service provided by Certified Crop Advisers for their clients.
Before installing a new tile drainage system, or upgrading an existing one, landowners should examine the feasibility of incorporating DWM components into the new design. Often systems for DWM need to be laid out with lateral lines parallel to the field contours, and mains running down the slope. New technology permits DWM systems to even be used on sloping fields, with a step control unit (WaterGate) inserted into the main line for each 12 to 18 inches change in elevation. If a new drainage system is put in place without considering DWM, it may not be possible to retrofit it for DWM to be added later, and the opportunity to manage drainage will be lost for decades to come.
Usually DWM can be incorporated into a new drainage system for about a 10% increase in overall investment in the system. A typical installation of a DWM control structure costs about $1,200. It may be possible to get cost sharing assistance through NRCS EQIP program for up to 75%, bringing the out-of-pocket cost to $400 or about $20/acre. Amortizing that cost over 20 years, the real cost of a DWM system can be less than $1 per acre per year. The potential savings in better water and nutrient management can be many times that amount. Benefits include potential yield increases, especially in dry years, and potential substantial reduction of nitrate losses from the field.
As pressures to increase crop production to meet the world’s growing demand for food, feed, fiber, and fuel, water management will be under increasing pressure. For many farmers, efficient water management will mean implementation of drainage water management. As new systems are installed and older ones upgraded, consideration of DWM possibilities should definitely be a part of the plan.