Will drainage stress my crop in dry years?
Tile drainage does not remove “plant available” water from the soil; it merely removes “gravitational” water that would drain naturally if unimpeded by confining layers in the soil. The greatest benefits of tile drainage typically are realized in wet years, but because drainage promotes deep root development, crops often will have better access to soil moisture in dry years. During extremely dry growing seasons, a tile-drained field certainly might have less available water at some point during the growing season than an undrained field.
Whether such an effect would offset the early season positive effects of drainage is unknown, and highly site- and year-specific. In general, where poorly drained soils exist, crop yields will be more uniform from year to year with tile drainage.
Drainage control structures (also known as controlled drainage or drainage water management) can be installed to provide the potential for limiting the release of drainage water into the ditch and conserve more soil water in the root zone. Similarly, the pump in a lift station can be turned off when drier growing conditions become a concern.
Can I install a tile drainage system myself or have a neighbor do it to reduce costs?
Do-it-yourself (DIY) tiling is certainly an option that is being considered by many farmers/ landowners. With good equipment, good design and the necessary commitment of time and resources, DIY tiling may be a sound option and may save on installation costs. However, like any other field operation, an investment in specialized equipment and knowledge is required for DIY tiling.
Tiling typically requires at least a four-person crew, a tile plow, electronic controls (global positioning system and plow control), a backhoe, tile cart, and several large and medium-sized tractors.
Pipe depth and grade, pipe size and field layout are all extremely important in design and will determine the quality of performance of your system. Above all, making sure the tile system is designed and installed properly is important so it will perform well for many years.
When do I need to use a “sock” drain envelope or fine/narrow-slot tile?
The need for an envelope (sock), or narrower slots, on the drainage pipe depends on the soil texture in the region of the tile depth in the field. Generally, poorly graded fine sands and coarse silts require the use of sock envelopes.
In general, clay, silty clay, sandy clay, silty clay loam, silts and loams do not require envelopes due to their natural cohesiveness. The Natural Resources Conservation Services (NRCS) Web Soil Survey website (http://websoilsurvey.nrcs.usda.gov/) can be used to determine the soil texture in the region of the tile depth.
If you have doubts or questions, then a soil sieve or particle size analysis should be done. This is a relatively easy mechanical procedure that can be performed by a commercial soil-testing lab or the soil-testing lab at NDSU. The analysis will determine the sand, silt and clay fractions of the soil, and the range of soil particle sizes.
No sock is needed if the clay fraction is greater than 30 percent. A sock may be needed if the medium to very coarse sand fraction (0.5 to 2 millimeter particle size) accounts for more than 20 percent of the total.
What is “controlled” drainage or “drainage water management”?
Controlled, or managed, drainage systems incorporate structures that allow the producer/manager to raise the outlet elevation at strategic locations in the drainage system to control the release of drainage water and potentially maintain a shallower water table.
Controlled drainage systems offer the potential to conserve soil water in the root zone and reduce drainage flows and the loss of dissolved nutrients (nitrogen and phosphorus) from the field. If the timing of rainfall is favorable, controlled drainage creates the potential to store water for drier periods during the growing season.
One or more special control structures, or the pumped outlet itself, may be used to control the drainage system. Control structures utilize stop-logs or baffles to set the desired water table elevation at the location of the structure; a pumped outlet may be turned off to create the same effect.
Considering the option of drainage water management in the initial design of the drainage system is important so that the layout of the system accommodates the goal of drainage management to the fullest extent and maximizes the effectiveness of the practice.
Typically, fields with average field grade from 0 to 0.5 percent are best suited for the practice, but other factors such as field slope uniformity and access to control structure locations are important, too. A field that is nearly flat may require only one control structure (or a pumped outlet) to implement the practice, whereas a field with more grade may require several control structures.
The benefit of drainage water management is that producers have one more tool to manage production risks. Under certain conditions, water retained with the control structures may increase crop yield.
Can I irrigate through the tile drainage system, or “subirrigate”?
“Subirrigation” is the practice of providing water to the root zone through a drainage water management system. If a source of irrigation water is available and the drainage system is designed appropriately, water can be introduced into control structures, special inlets or the sump of a pumped outlet to raise the water table and make water available to the crop.
To make this practice work, a sufficient source of water is needed to supply the water needs of the crop, usually during July and August. As with drainage water management, for this practice to be effective, the subirrigation system must be designed before installation of the tile. A system designed for subirrigation generally will require closer drain spacing than a system designed only for conventional drainage.
Are any water quality issues associated with tile drainage?
The water quality impacts of tile drainage are positive and negative. In general, when compared with surface drainage only, phosphorus and sediment losses via surface runoff are lower from tile-drained fields, while losses of nitrate-nitrogen and other dissolved constituents in the root zone are greater. The extent of the increase or decrease of these constituents also depends on farm management practices, and the magnitudes of the losses are highly variable from year to year.
What is the relationship between tile drainage and downstream flow and flooding?
Tile drainage impacts on downstream flow and flooding have been the subject of much debate for more than a century. The influence of tile drainage on stream flow involves complex processes that depend on many factors. Therefore, generalizations such as tile drainage “causes” flooding or tile drainage “prevents” flooding oversimplify the issue.
(Built by the North Dakota State University 2021)
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