April 1998
University of Minnesota Small Grains Specialist
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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
Watch your seeding depth this spring, because it's an important factor to good stand establishment.
If seeds are planted too deep, the young seedlings may not be able to reach the soil surface. During the process of germination, the young seedling uses the stored energy of the kernel to grow and reach the soil surface, so that the leaf tissue can start photosynthesis and the plant is no longer dependent on the energy reserves of the kernel. Seeding too deep increases emergence time and reduces the vigor of the young seedling. This in turn can lead to stand reduction and ultimately yield losses.
On the flip side, seeding too shallow increases the risk of moisture stress. Seeding depth should not exceed 1 ½ to 2 inches for small grains and especially with semidwarf wheat, proper depth control is more critical because of a shorter coleoptyle.
Table 1 illustrates the difference in coleoptyle lengths between some common wheat and barley varieties. Note that there is a fairly good correlation between plant height and coleoptyle length. The coleoptyle is a leaf-like structure, which protect the first true leaf as both grow towards the soil surface. Planting a variety with a shorter coleoptyle too deep will force the seed to form a subcrown internode to move the growing point towards the soil surface. This requires energy, delays emergence and further stressing the young seedling.
Getting proper seeding depth requires some attention to detail. Reducing operating speeds to less than four miles per hour increases depth control considerably on both press drills as well as air seeders. In any case make sure that the depth controls are adjusted properly, since seeding depth will vary from field to field simply because of soil type, seedbed preparation, and the available soil moisture.
Seeding Rates
In 1997 for the second year, I have conducted a seeding rate trial at the Northwest Experiment Station. I have shared some of the results at grower meetings this past winter, but have summarized a few of the findings for you here.
The initial stand is an important first step towards maximizing your yield potential. To obtain an optimum stand, we need to know:
1) number of seeds per pound of seed
2) percent germination
3) expected stand loss in the field
4) desired number of plants per acre
The first two points are seedlot specific and will need to be determined for every single seedlot you plan to use this spring. The expected stand loss is the number of seeds that will not become a healthy seedling despite the fact that the seed is viable. Stand loss is a function of the condition of the seedbed, the planting depth, soil temperature, etc.
In addition, as you increase the seeding rate, a number of seeds will not germinate despite the fact that they are viable. A number that is often used for stand loss is 10%. In the past two years, the average stand loss in the seeding rate trial was 20% for 1.25 million live plants per acre. This was in spite of a good seedbed and careful depth control. Obviously this means that total number of live seeds that need to be planted is not 1.38 million live seeds per acre but rather 1.5 million live seeds per acre. I obviously don't know what your historic stand losses have been. However I encourage you to calibrate your seeding rate properly and verify your stand by using a stand count as you scout for weeds.
The desired number of plants is what we are ultimately interested in. The 28 to 30 plants per square foot or 1.25 million plants per acre is an average number for hard red spring wheat, which is still very valid. This number is adjusted downwards to 1 million plants per acre in western North Dakota.
As you start to plant later than the optimum seeding date (which I hope we will not have to do this spring), you need to increase your seeding rate with 1% per day for each day after the optimum seeding date to compensate for the expected reduction in yield potential. n