When soils have a high water table (poorly drained or somewhat poorly
drained soils) 
removal of the
excess water is necessary to promote adequate root growth. This will be
beneficial for both cropland and forest land in terms of increasing production
as well as some other benefits such as easier logging and site preparation. In
agricultural land, lowering the water table by subsurface drainage also allows
soils to warm more rapidly in the spring, because it takes less energy to heat
dry soils than wet soils.
Many of the soils of southern Minnesota require tile
drainage to increase crop production. Tile drains are
installed below the water table. The trench is
opened by a machine, the tile is installed, and the ditch is back-filled with
soil. The tile has small openings that will allow water to enter the tile when
the soil is saturated. Tile drains remove only the water that is wetter than
(or the potential is greater than) -0.33 bars (that is, the gravitational
water). Water that moves into the tile lines will contain the soluble nutrients
(especially nitrogen) or pesticides that are in the soil. During the spring of
the year these tile lines will be very active in delivering water to drainage
ditches.
The ditches will deliver the water to local streams and rivers and eventually the Minnesota or Mississippi River.
The installation of tile drainage in Minnesota has removed many of the natural wetlands. To see the impact on a small watershed (Seven Mile Creek Watershed of he Minnesota River) go to this link=Seven Mile Creek
Tile drains are also used around basements
to remove the free water that can accumulate near walls. If this is not done,
water could move from the soil into the basement or you have a
wet basement
Container soils have special requirements when it comes to the soil water.
The taller the pot, the taller the column of water and the lower the soil water
potential that can be reached. Very small pots have a very short column of
water, and whenever a small quantity of water is added, they are very close to
saturation or have a high water potential, and therefore, have low oxygen
levels.
The opposite of too much water is not enough water. Probably more agricultural areas in the U.S.A. have this problem than those that have too much. The use of irrigation to provide supplemental water to agricultural systems has been practiced for centuries. Irrigation works existed in 3500 B.C. in Mesopotamia. Go to Mesopotamia for more information. Information about the societies decline as the soils became salty from irrigation is found at collapse of Mesopotamia. Today, irrigation is a way of life for agriculture in the arid west and is also needed on some of the sandy soils in Minnesota. The type of irrigation system selected will be dependent on soil and landscape positions.
Click on the "type of irrigation" to see an example.
Flood and Furrow Irrigation-Flood in Az.- Diagram
Furrow irrigation is used in the Salinas Valley of California for vegetables.
This irrigation system requires a medium-textured soil to allow water to travel
down to the furrow and not seep in at the entry end. Slope requirements are 1
to 2%. Flood irrigation, which is similar except the whole field is flooded,
also requires similar conditions. On sandy soils, this system would not work
because of too-rapid infiltration.
Sprinkler Irrigation
Sprinkler irrigation is where water is sprayed from overhead. This system is
more tolerant of variable soil textures since the rate of application can be
more adequately controlled. Also, slopes can be more varied and up to 15%.
Sprinkler systems that move over the landscape can also be used. In Nebraska
and western Iowa, pivot irrigation systems cover as much as 640 acres. The
system moves around a central pivot, giving a large circular pattern of
irrigated agriculture when seen from the air, or they can move laterally across
the field as seen here.
Subirrigation Field -Diagram
Where the water table is close to the surface and can be controlled by ditches
or pumping, subirrigation can be used. This is frequently used on organic soils
where the water table is raised to moisten the soil and then lowered again
after the soil is at field capacity. Celery is growing in this field of peat.
Drip Irrigation -Diagram-Comparisons
Drip irrigation was first developed in Israel to conserve irrigation water,
while at the same time avoiding erosion from irrigation. Water is continually
added to the soil-one drop at a time. This keeps the soil at, or just below,
field capacity, but only in the immediate area of the root zone of the crop.
This system has been used extensively on vineyards and orchards in California,
especially on very steep areas. This method saves labor, but has a high cost of
installation.
Irrigation - More Information.
Water is supplied to the farmer in the west by various
irrigation canals, such as the California Aqueduct, the Arizona Project, and
others. The cost of this water, when all factors are considered, has been
greatly subsidized by the general public. If agencies charged farmers the
actual cost of the water, they would not be able to afford it at today's
agricultural commodity prices. 
During times of drought (In general, drought is defined as an extended period–a season, a year, or several years–of deficient rainfall relative to the statistical multi-year average for a region), adequate water supplies may not be available for agriculture as was the case in California in 1976-77. A new study reports that northern Great Plains droughts have recurred at roughly 160-year intervals. (Jim Clark-Duke Un.) Another study from Iowa suggest that drought is on an18 year cycle in the upper midwest due to the lunar cycle (Louis Thompson, Iowa St. Un.). Nebraska is currently in a drought.Lake-McConaughy-August2-2006
In Minnesota irrigation water is either from surface lakes or ground water via wells. Minnesota's irrigated crop acreage continues on the upswing (Jerry Wright, University of Minnesota). Most of the new acreage was irrigated with center pivots. The most recent figures, from the year 2000, show 432,888 acres irrigated in Minnesota in the summer of 2000. The irrigated acreage for 2000 was registered under 4,150 DNR irrigation permits.
Soil Water Chapter 5
Soil Water Chapters
© Terence H. Cooper & Regents of the University of Minnesota, 2007. The University of Minnesota is an equal opportunity educator and employer.
