Wheat is being harvested in the region. These fields will be without a crop during the fall. This would be an excellent time to work on water management for the coming season such as maintenance of field ditches. One of the newer management practices is to put tile (plastic pipes) below the surface of the field in order to increase sub-surface drainage. Again during the growing season of 2005 wet conditions prevented some fields from being planted on time. In other fields crop maintenance, like spraying herbicides and fungicides, has been a challenge (Figure 1). There are still many questions among producers about tile drainage. Some of the major concerns and answers are discussed below.

Tile Drainage won’t work on flat ground
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 (Figure 2). Pumped outlets add to the initial outlay 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.

The economics just aren’t there for commodity crops
The economics of tile drainage systems depend on crop yield response, initial capital outlay for the materials and installation of the system, and any annual operation and maintenance costs (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 the crop produced, 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 water table is 15”-20” below the surface for extended periods of time, on a clay loam soil. Drainage systems can return the cost of investment in as few as 3 to 10 years, when conditions are wet.

Tile drained soils warm up faster in spring
True! Research in Crookston and Brooks, MN shows that tile-drained soils do warm faster—in particular at 12” – 24” depths. The extent of soil warming depends on how much water is in the soil and the soil type. Other benefits of tile drainage include more uniform drying of the field, less soil compaction, less wear and tear on equipment and reduced fuel costs for field operations. Spring field operations on tiled fields may be advanced from several days to over a week compared to fields without tile drainage. How much earlier depends on the timing of spring rainfall. 

Tile drainage adversely affects water quality
While it is true that nitrate-nitrogen loss from tile-drained fields has been a problem in the upper Midwest for the corn-soybean rotation, it is probably incorrect to make a general statement like this for the Valley. Tile drainage can increase the loss of soluble constituents (e.g., nitrate, salts) but in reducing surface runoff, tile drainage can reduce the loss of other constituents such as sediment and phosphorus. Sediment and phosphorus losses cause problems for local receiving waters while nitrate-nitrogen losses pose a threat to coastal ecosystems and for downstream drinking water consumption. 

Tile drainage is increasing in NW MN and farmers who started tiling have continued to expand their tiled acres. It is recommended that producers interested in tile drainage discuss their options with a qualified contractor, experienced neighbor, engineer, or Extension, before making a decision. There are a number of resources available to address tile drainage questions and issues, and Extension conducts annual tile drainage workshops (scheduled for February 21 & 22, 2006 in Moorhead and March 7-9 in Mankato) 

U of M Tile drainage information on the Minnesota Wheat Growers website can be found at: 

http://www.smallgrains.org/drainage/home.html

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