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            AGRONOMY NOTES NO. 182
    Some time ago, I got a call from Stan Bruce with the Federal Crop Insurance Program
asking about test weights for some of the less commonly planted crops in Montana. Stan's
question started me digging and before long I came up with some useful information that
I thought would be worth sharing with readers of Agronomy Notes.

If you want to check out a web site, which was the source of most of the following
information, go to:


   Also, attached to this web site is a seeding rate calculator, which can be used to
determine the amount of seed to plant to get the desired population (more on that later).

   To start with, it would be a good idea to clarify a few of the terms used in this note.
According to the authors of the web page, "Crops should be seeded with the expected
plant population in mind, which means the 1,000 kernel weight must be known." And,
the authors suggest that seeding rates and plant populations are something that should be
customized to each farm, field, and location.

   "The 1,000 kernel weight is a measurement of the weight in grams of one thousand
seeds of a grain sample. It varies from one variety to another and from one crop type to
another. In fact the 1,000 kernel rate of a single variety will vary from year to year and
from field to field. By using the 1,000 kernel rate, a producer can account for these
variations when determining the ideal seeding rate and calibrating seed drills. Using the
actual 1,000 kernel weight of the seed you plant may save you money, especially with
large seeded crops."

   "Seed quality is important when using the 1,000 kernel weight. Plump, large seed
produces the most vigorous plants. Poor seed produces weak plants. Use seed that has
had foreign material and small, shrunken or misshapen kernels removed. To properly
calculate seeding rates and calibrate seed drills, germination tests should be done on all
seed lots. An estimate is also needed of seedling mortality, that is all those seeds that
germinate but fail to develop into a plant. The reasons for plant death include disease,
insects, rocks and drought. A common value used for mortality is 3%."

   Here's something else I did not know: "Seeding the same amount of seed (bu/ac) each
year won't mean you always get the same plant population. Barley seed, for instance, can
vary 25 per cent in size and weight, both of which can dramatically affect the final plant
population. Differently shaped seeds flow at different rates in the drill. Because of this,
you should use the actual thousand kernel weight of your own seed when calculating seed
rates and calibrating seed drills."
   Seeding rate is an important factor when considering all the decisions that need to be
made at planting time. For instance, a high seeding rate can result in: higher crop yields,
better weed competition, earlier maturity, fewer tillers, smaller seed size, and shorter
plant height.

   Calculating Seeding Rates: To calculate the seeding rate in pounds per acre you need
the following information:
     Desired plant density in plants per square foot
     Germination rate (%)
     Emergence mortality (%)
     Row spacing in inches
     1000 kernel weight in grams

   It is a good idea to make sure you have a value for the 1000 kernel weight (in grams).
Otherwise, you will need to count out 1,000 seeds and weigh them (grams). The postal
service has good scales. Remember that 1 ounce equals 28.3 grams. So, if you weigh
1000 kernels in ounces, multiply by 28.3 to get grams of seed per 1000 kernels.

   The germination rate is specified on the seed tag when you purchase your seed. You
will need to correct for emergence mortality, which should not be more than a few
percent. With the above values, you can use the calculator to get the desired seeding rate.
For now, if you are looking for some suggested seeding rates, here is a summary of the
information contained in this web page:

                        Commonly Accepted Cereal Seeding Rates
                        Desired Plant Population       1,000 Kernel Seeds per lb
                       Per sq inch     Per sq foot Weight (grams)        Average
 Wheat (hard red)          250             24           30-40         11,000-15,000
  Wheat (soft              210             24           30-40             14,200
     Barley              210-250           20-24              30-45          10,000-15,000
      Oats                 250              24                30-45          10,000-15,000
      Rye                  250              24                30-35          13,000-15,000
    Triticale              310              30                34-35          10,000-13,000
  Corn (sweet)             5.0              0.5                380               1,200
     Grain                 6.1              0.6                380               1,200
     Silage                7.6              0.7                380               1,200

                                     Special Crop Seeding Rates
                          Desired Plant Population         1,000 Kernel Seeds per lb
                         Per sq inch     Per sq foot    Weight (grams)      Average
         Pea                 75               7            125-300        1,500-3,600
         Bean                25              2.4           200-350        1,300-2,300
         Fababean            45              4.3           350-425        1,000-1,300
         Lentil           105-147          10-14              30-80          5,600-15,000
         Soybean             50              5               100-200          2,300-4,500
         Buckwheat          150             14                  30               15,100
         Safflower           50             4.8                 35               12,600
         Confection         4.5             0.4                175                2,600
         Oil                6.0             0.6                126                3,600

Now, back to this seeding rate calculator. I decided I would make an attempt at using the
calculator. For instance, for winter wheat:

            Plants/ft 2                    15           15              15           15
          Germination                     95%          95%             95%          95%
       Seedling mortality                  3%           3%              3%           3%
          Rowspacing                       7"           7"             11"          11"
    1000 kernel weight grams               30           40              30           40
   Grams of seed per 100 feet of           27           37              43           58
       Seedling rate, lb/ac                47           63             47            63

    Calibrating seeding equipment (an easy method): The following procedure involves
pre weighing the amount of seed needed per 100 feet of row. You will need a clear plastic
measuring cup or tube (any narrow container will do, even an empty pop bottle with the
top cut off). Use the calculator to calculate the weight of seed needed per 100 feet of row.
Weigh the required amount of seed and pour it into your calibration tube. Mark the tube
for future reference in the field. Hang a bag or collection container on one run of the seed
drill and drive 100 feet. Pour the seed from the collection bag into the calibration tube to
see if the correct amount is coming through. Adjust the drill setting and repeat the
procedure if necessary. Catching the seed from more than one drill run will increase
overall accuracy.

   One more simple conversion: Collect the seed that would be planted in 100 feet of row
by placing a bag over one of the openers. Weigh the seed. The actual seeding rate can
then be calculated as follows:

   Seeding rate = grams of seed/100 feet of row x 12/row spacing. For example, if the
grams of seed per 100 feet of row is 39 and the row spacing is 7 inches, then the seeding
rate is equal to 39 grams x 12/7 = 66.8 lbs/acre

Categories: Seeding Rate, Wheat Agronomics
Date: 1999

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