Morris J. Bitzer and James H. Herbek Grain Crops Extension Specialists

Planting precision is one of the most critical steps in producing a successful wheat crop. Proper planting procedures include time of planting (Oct. 10-30), depth of planting (1-1.5") and seeding rate (35 seeds\ft2). The objective is to establish a crop that will have 30-35 plants\ft2 that are well developed (1.5 tillers/plant) by winter dormancy. To accomplish this objective, this article will discuss (1)how to determine the proper seeding rate and (2)how to calibrate your drill to deliver the proper seeding rate.

Seeding Rate and Seed Size

Proper stand establishment requires that seeding rate be determined in terms of number of seeds per unit area (per square foot or linear row foot) rather than pounds or bushels per acre. Seed size will vary among varieties and even among seed lots of the same variety. Seed size or the number of seeds per pound can vary from 10,000 seeds per pound to 20,000 seeds per pound.
1. The linear length of row needed to drill
       35 seeds/ft2 is calculated by dividing 144
       square inches in a ft2 by the drill row
       width For example:  Using a drill with 7  
       inch row width, dividing 144 by 7 = 20.6  
       inches of row length for 35 seeds at 90%
       or greater germination.  The following
       chart can be used as a guide to  determine
       the optimum seeding rate based on a
       germination of 90% or higher.
                     Length of row     Seeds/row foot needed*
   Row width            needed for 1 ft2    35 seeds   30 seeds
        (inches)      (inches)              per ft2    per ft2
           4            36.0                     12          10
           6            24.0                     18          15
           7            20.6                     20          17
           8            18.0                     23          20
          10            14.4                     29          25   
* In fields where yields are not expected to be
         quite as high, establishing from 25-30 plants/ft2
         will require only 30 seeds/ft2.  If planting time
         is delayed, increase seeding rates by 2-3
         seeds/ft2 (1-2 seeds/row foot) for every two
         week delay beyond the optimum planting date.
2. The following chart can be used to calculate pounds per acre needed if the seed size is known.
     Seeds per      Seeds/square foot*.
               pound             35       30    

                                      Lbs/acre   .
              10,000            150       131
              12,000            127       109
              14,000            109        93
              16,000             95        82
              18,000             85        73
              20,000             76        65       .
*Based on 90% or greater germination
If the number of seed per pound is not
      stated on the seed tag, you can determine
      as follows:
 l.  Weigh a 20 gram representative
2. Count the number of seeds in the sample. (Do this at least 3 times.)
3. Multiply the number of seeds counted by a factor of 22.68. This equals seed per pound.

Calibrating The Drill

If your variety has 12,000 seeds per pound, then seeding at 127 lbs/acre in a 7 inch row width will place 35 seeds/ft2 in the ground. However, because seeding rate charts on drills are not precisely accurate and because size and shape of seed can affect seed delivery, it is still best to calibrate the drill based on seeds delivered per unit area.
Hook the tractor to the grain drill so the drill's drive gears can be engaged and jacked-up more safely. Jack-up the drive wheel just so it clears the ground. Turn the wheel several revolutions to be sure all working parts are turning freely. Check all spouts to be sure they are not partially blocked.
   l.  Determine the mumber of revolutions
         the drive wheel must turn to travel 50
a. Measure the distance around the drive wheel. Example = 60"
Inches traveled in 50 feet = 50 ft x 12 inches/foot = 600 inch distance.
Number of tire revolutions per 50 feet = 600 inch travel distance divided by 60 inches per tire revolution = 10 turns of the tire per 50 feet.
     2.  Determine the number of seeds needed
         for distance you will travel to calibrate
         for a 7 inch row width..
         a. 50 feet of row x 20 seeds/foot of row
            = 1000 seeds.

     3.  Count out 1000 seeds of the seed lot to
         be planted and put the seed in a
         graduated tube such as a rain gauge of
         other guage or other clear tube and mark
         the level of 1000 seeds in the tube.

     4.  Set the drill on a rate expected to be
         close and turn the wheel the number of
         revolutions needed for 50 feet while
         catching the seed from one row.  Pour
         the seed caught in the  pre-calibrated
         tube for 1000 seeds and check the level.
         Repeat for each of the rows caught.

     5.  Change settings and repeat until the
         appropriate number of seeds is obtained
         (level marked on tube).

Adjusting Wheat Seeding Rates For Germination

   1.  If germination is below 90%, then
         wheat seeding rates should be adjusted.
2. Calculate seeding rate adjustments for germination by dividing the desired seeding rate (seeds/ft2) or (lbs/acre) by the percent germination.
Examples: a. 35 seeds/ft2 divided by 85% germination = 41.2 seeds/ft2. b. 127 lbs/acre divided by 85% germination = 149.5 lbs/acre.

A seeding rate of 149.5 lbs/acre will be needed to produce 30 to 35 plants/ft2 based on 85% germination.