Frequently asked questions about Tile in ND

1. Frequently Asked Questions about
Subsurface (Tile) Drainage
Gary Sands, University of Minnesota Extension Engineer, Tom Scherer, NDSU Extension Engineer, and Hans Kandel,
NDSU Extension Agronomist
1. Why is there an increased interest in tile drainage?
Tile drainage installation has been accelerated in North Dakota in the last decade. The recent
adoption of this technology in the region is mainly due to increased rainfall since 1993, and
prompted by higher land values and better crop prices. In the spring many farmers have been
unable to plant the crops in a timely fashion due to the wet conditions. The increased rainfall also
caused salinity to become a problem due to rising water tables. Salinity in the Red River Valley
alone encompasses over 1.5 million acres and accounts for about $50 to $90 million in lost
revenue. Tile drainage is a promising management practice to control and reduce salinity in wet
soils.
2. Are my soils too tight (clayey) to tile drain?
Tile drainage has been practiced on may soil textures. Sandier soils can be drained with deeper,
widely spaced tile, but tend to need sock filters around the pipe to prevent soil particles from entering
the tile. Soils with a higher clay content can also be drained but require tile to be placed shallower
and closer together. A typical design for a Fargo clay might be a depth of 3 feet with a spacing of
40 feet, whereas tile spacing for a Ulen fine sandy loam would be around 100 feet. Soils where
shrinking/swelling clays or peat predominate, or sodic soils may need special consideration with
regard to tile drainage.
3. Aren't my fields too flat to drain? How would I provide an adequate outlet for a tile
drainage system?
Level fields can be drained as long as minimum grades of 0.05 to 0.1% are maintained for tile laterals. A tile
at 0.1% grade has 1 foot of fall per thousand feet. On level ground this means that the tile depth
would vary by 1 foot over 1000 ft. A typical drainage system provides an outlet where tile can
drain freely (by gravity) into a surface ditch. Where topography does not allow for a gravity outlet,
pumped outlets are used, provided a surface waterway exists to discharge the drainage water. A
pumped outlet or "lift station" provides the lift required to get the drainage water from the
elevation of the tile, to the ground surface and into the receiving waterway. Pumped outlets add to
the initial investment and operation/maintenance costs of the drainage system, but have proven to
be economically feasible in many situations. A pumped outlet station includes sump, pump, and
discharge pipe. Important design features include size and shape of sump and capacity of the pump.
4. What negative effects on farming am I experiencing now due to inadequate drainage?
Often, the major source of “damage” from inadequate drainage relates to timeliness of field
operations. Inadequate drainage can delay spring field operations from days to a week or more.
Occasional wet spots also interrupt field traffic patterns and cause field operations to be less
uniform. Machinery traffic on soils that are too wet will cause increased soil compaction. Delays in
planting mean a shorter growing season for the crop. Once the crop is planted, inadequate drainage
can cause stunted and shallow root growth, and sometimes, complete crop failure due to excess-
water stress (lack of oxygen in root zone). Planting delay, soil compaction, and excess-water stress,
combined, can translate into significant crop yield impacts. The magnitude of the yield impact for a
growing season depends on crop and variety, soils, and the season’s rainfall pattern.

2. 5. What do the economics look like for tile drainage, for the crops that I produce?
The economics of tile drainage systems depend on crop yield response, initial capital investment
for the materials and installation of the system, and any annual operation and maintenance costs
(like electricity for pumped outlets) involved. While crop yield response to drainage can be
assessed directly, the impacts of inadequate drainage on soil quality (structure, microbial activity,
etc.) are more difficult to measure and assign economic value. Most field crops show a positive
response to drainage, often with the best response from a combination of surface and tile drainage.
The level of yield increase for a given year depends greatly on how poorly drained the soil was prior to
drainage, and seasonal rainfall. Typical yield increases might be 10-30 bu/ac for corn and 5-10
bu/ac for soybeans. Wheat has been shown to yield only 58% of potential yield and sugarbeets 71% of
potential yield when the watertable is 15”-20” below the surface for long periods of time, on a clay
loam soil. Besides the increase in yield there are also reductions in operating expenses on the farm.
6. How will tile drainage affect my overall farming operation?
Tile drainage will cause soils to warm-up and dry out faster in the spring. Fields with intermittent wet
spots will dry out more uniformly. Spring field operations on tiled fields will most likely be
possible at an earlier date than fields without tile drainage. Timely spraying of crops can be expected.
7. Drainage may be great in wet years, but won't I stress my crop in dry years?
Tile drainage does not remove plant available water from the soil. Clearly, the greatest benefits of
tile drainage are realized in wet years--but because drainage promotes deep root development,
crops will have better access to soil moisture in dry years. During extremely dry years it is
conceivable that a tile-drained field might have less available water at some point during the
growing season than an undrained field. Whether or not this would offset the early-season positive
effects of drainage is unknown. In general, where poorly drained soils exist, crop yields will be more
uniform from year to year with tile drainage. Water table control structures can be used on fairly level
fields, which provides the producer the option to close the outlet and conserve water when needed. A
pump unit could be switched off when there is a concern about dryer growing conditions.
8. Are there water quality issues associated with tile drainage?
The impacts of tile drainage are a mixed bag with respect to water quality some positive and some
negative. In general, phosphorus and sediment losses from tile drained field decrease, while losses
of nitrate-nitrogen and other dissolved constituents may increase. The extent of the increase or
decrease also depends on farm management practices.
9. What will tile drainage do to downstream flow and flooding?
Surface drainage increases peak surface runoff flow rates. Tile drainage typically reduces both
volume and peak of surface runoff from agricultural fields. Studies show that the overall volume of
water lost (surface runoff and tile flow combined) from a tile drained field may increase slightly (5-
15%), compared to fields with surface drainage only. Flooding is generally dependent on peak
surface runoff rate. Tile drainage tends to decrease peak runoff rates, this suggests that tile drainage
should not increase (and may decrease) the incidence of flooding. Flooding in general, is a
watershed-scale phenomenon, and the effects of tile drainage at this scale are not as well understood
as the field scale.
10. Could I install a tile drainage system myself, or have a neighbor do it, to cut cost?
Self-installation should be carefully considered. One of the most important benefits of using a tile
installer is experience and familiarity with design procedures and standards of tile drainage
systems. Depth, grade, pipe size, and field layout are all extremely important in design and will
determine the quality of performance of your system. Tile not properly installed may not work as
anticipated.