Shallow water tables can impact crop production, said Daniel Ostrem, South Dakota State university Extension water resource field specialist.
"The water level underground can greatly benefit the crop or hinder its growth depending on where it is located in respect to the plant's roots," Ostrem said.
Tile can help manage water tables to increase land productivity but needs to be carefully installed and managed to maximize production and minimize any adverse impacts it may create, Ostrem explained.
He added that before a tile system is installed, it is a good idea to survey the field in order to determine what kind of system will provide the greatest benefit while keeping in mind possible future changes or additions.
"It is helpful to view a drainage system as not just controlling occasional wet spots at the surface after heavy rain, but managing the whole water table within the field," Ostrem said.
There are three main systems that can be utilized to control the level of the water table. The three systems are explained below.
Conventional: This system is the most well-known and requires the least amount of maintenance. It is designed for lowering the water table only by free drainage from the field.
Controlled: This system, also known as drainage water management, it is a controlled design which allows the producer to manage the outlet for either drainage or to conserve additional water in the soil profile, but control is limited to current environmental conditions. While the producer can lower the water table when needed, he or she is only able to raise the water table if enough water is naturally entering into the field.
This additional management ability is obtained by the use of gates on the tile lines that either back up water into the tile or are opened to allow slow or free drainage to occur.
Subirrigation: This is a system very similar to a controlled design but with the ability to add water back into the tile to raise the water table.
Subirrigation requires the greatest cost, engineering, and maintenance. Irrigation should be managed to meet the needs of the crop while keeping in mind the risks involved with a high water table. The water table is managed at a level that provides for crop uptake to meet the water demand but not so high as to reduce aeration in the upper root zone and limit crop development.
Once the type of system to be installed is determined, then a layout can be chosen. Ostrem explained that there are two main types of layouts; targeted, sometimes called random; and parallel, or pattern, drainage.
In South Dakota targeted drainage is the most common layout because it minimizes the upfront costs by only placing tile in the lower areas where they will be most effective in removing water from the field.
A parallel layout is best utilized where the entire field is poorly drained. It creates a series of equally spaced lines that covers a larger area typically than a targeted layout. Parallel drainage has a greater cost with a greater length of lines installed but it also influences a greater area for improved production. A cost/benefit analysis is very important to determine your return on investment when choosing a design layout.
"A drainage or subirrigation system designed for water table management can have a large influence on many environmental factors," Ostrem said.
More information on the effects of tile can be found by visiting http://igrow.org/agronomy/corn/tile-drainage-imapct/.
This information is only a brief introduction into the broad design concepts of managing water tables. More information on starting a drainage design can be found at http://igrow.org/agronomy/corn/evaluating-tile-drainage-design/.