ISSUE 14   August 21, 2008

SUB-SURFACE DRAINAGE

Although the 2008 growing season has been generally dry in the western part of ND, there was excess rainfall in the Red River Valley in June and notably large amounts of rain in the second week of August. Saturated conditions early in the season usually have a negative impact on crop production. Now at the end of the season, excess moisture can set back the harvest of cool season crops. Delayed harvesting may result in reduced crop quality. Although many agricultural producers have developed field ditch systems to remove the surface water quickly, managing excess moisture in the soil profile is still a relatively new farm management practice.

Tile drainage installation (sub-surface drainage) has increased 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, better crop prices, and high input costs. In many years producers have been unable to plant crops in a timely fashion, in the spring, due to the wet conditions. Delayed planting of cool season crops reduces the yield potential. Tile drainage allows soils to warm-up and dry out faster in the spring. Spring field operations on tiled fields will most likely be possible at an earlier date than fields without tile drainage.

Increased rainfall also has caused salinity to become a problem due to rising water tables. Tile drainage can potentially control and reduce salinity in wet soils. Salt is removed when water moves through the soil profile. This process of land reclamation may take a few years and depends on the amount of rainfall and leeching of the salts out of the soil profile via the tile. Some impacts of tile drainage with respect to water quality are positive and some negative. In general, phosphorus and soil particle losses from tile drained fields decrease, while losses of nitrate-nitrogen and other dissolved constituents (salts) increase.

In the Red River Valley many of the fields do not have much fall. 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 of tile. A typical tile drainage system provides an outlet where water 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. Pumps add to the initial investment and there is a cost to operate and maintain the lift station.

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. In general, where poorly drained soils exist, crop yields will be more uniform from year to year with tile drainage. The newest technology incorporates a control structure in the tile line which provides the opportunity to manage the water table in the field and therefore even further reduce the production risk. With a control structure there is the opportunity to let some water out in the spring to provide the ideal planting conditions. During the summer the control structure could be set to retain water for crop production or let water flow out of the tile in case of excess moisture conditions.

A research field has just been established on one of the NDSU research farms (NW 22) to collect data on the crop response to tile drainage of major ND agricultural crops.

tile plough
Tile plough installing tile on a NDSU research site.

Hans Kandel
Extension Agronomist Broadleaf Crops
hans.kandel@ndsu.edu

 

INFLUENCE OF RAIN ON GRAIN READY TO HARVEST

In parts of the state we recently had significant rainfall on mature grain that was nearly ready to harvest, some of it was even laying in the swathe. A frequently asked question this past week was how will this rain impact test weight? Test weight is a measure of density or the weight of grain in a given volume. Test weight, therefore, measures the weight of the kernel and how well the kernels "pack" into a standard cup when filled using a standard process. The weight of the kernel will not be affected by rainfall unless, of course, it remains wet enough for germination to begin. Wetting can effect how well the kernel packs. A dry kernel that imbibes water will swell. When the kernel dries down, it will have a slightly different shape (it begins to wrinkle) than before it imbibed water. This altered shape will not pack as well as the original, sound kernel, so test weight tends to decline after a wetting event. The good news is that a single wetting event usually has a limited impact on test weight. However, if grain is subject to repeated cycles of wetting and drying then test weight can decline dramatically. Research conducted with soft wheat in the eastern US found that test weight declined about 1.2 lbs/bu for every wetting and drying cycle. For more on this study follow this link:

http://www.ext.vt.edu/news/periodicals/cses/2006-06/wheattestweight.html.

Perhaps of greater concern is the impact on the grain of prolonged wetting on pre-harvest sprouting and falling numbers. Sprouting can render the grain unusable in the milling and brewing (in the case of barley) industry and as a seed source. Most hard red spring wheat varieties are dormant for a period after maturing and resist pre-harvest sprouting (PHS), even when appropriate environmental conditions exist. White wheat tends to be very susceptible to pre-harvest sprouting. There are, however, differences in varietal response in pre-harvest sprouting within the red wheat class. The University of Minnesota regularly screens new varieties for their propensity for pre-harvest sprouting. This information can be found at:

http://www.maes.umn.edu/08varietaltrials/redspringwheat.pdf.

If no visible sprouting is observed in the harvested grain that has been wetted before harvest, I would recommend that you still conduct a falling numbers test on grain intended for use as seed. Low falling numbers indicate that the seed lot had begun the germination process. Seed lots will low falling numbers, even though they may have good germination, have been found to have low seedling vigor and should be avoided as a seed source.

 

PLANTING WINTER WHEAT IN 2008

In the parts of the state that were not ravaged by drought, winter wheat yields were good again this season. If you are planning on planting winter wheat this fall, the following are a few suggestions:

  • Planting date: The optimum planting date for the northern half of the state is September 1-15 and for the southern half September 15-30. The last date that winter wheat can be planted will depend on the weather. The seed must germinate in the fall so that the crop will be vernalized in the spring. A larger plant will over winter better than a seedling or a sprouted seed.
  • Planting depth: Adequate moisture for establishing winter wheat is often a concern as the soil profile is usually depleted of moisture in the fall. If there is little or no moisture in the soils surface, planting shallow (1 to 1.5 inches deep) and waiting for rain is recommended.
  • Seeding rates: Generally a seeding rate of 900,000 to 1 million viable seed per acre is adequate. Higher seeding rates may be appropriate if planting late or when planting into poor seedbeds.
  • Plant in to crop residue: The best winter survival is achieved when winter wheat is no-till planted into standing crop residues that are able to catch and retain snow. Planting winter wheat into a low residue crop such as soybean increases the risk of winter kill, so only the most winter hardy varieties should be grown (see data on winter survival in 2005/06 in the following table and at www.ag.ndsu.nodak.edu/aginfo/smgrains/WWsurvial.htm.
  • Variety selection: In addition to agronomic characteristics such as plant height, yield, and disease and lodging resistance, also carefully consider the winter hardiness of a variety. In many years there is a direct correlation between winter survival and yield. Yield data from the 2008 season are being posted on the Small Grains Page http://www.ag.ndsu.edu/smgrains/. Data from previous years’ trials are available at http://www.ag.ndsu.edu/variety/index.htm.  Sources of certified winter wheat seed are ND State Seed Department or at the Small Grains Page.
  • Joel Ransom
    Extension Agronomist for Cereal Crops
    joel.ransom@ndsu.edu


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