Calculating the Amount of Seed to Plant

By Jim Bauder
MSU Extension Soil and Water Quality Specialist

For some answers, turned to a web site developed by the Alberta, Canada office of Agriculture, Food and Rural Development (http://www.agric.gov.ab.ca/).

Seeding rates and plant populations should be customized to each farm, field and location, according to the site's authors. In addition, crops should be seeded with the expected plant population in mind, which means the 1,000-kernel weight must be known.

The 1,000-kernel weight is the weight in grams of 1,000 seeds of a grain sample. It varies from one variety to another and from one crop to another. In fact, the 1,000-kernel rate of a single variety will vary from year to year and from field to field. Using the 1,000-kernel weight allows a producer to account for these variations when determining seeding rate and calibrating seed drills. It might even 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. You should use seed that has had foreign material and shrunken or misshapen kernels removed. To calculate seeding rates and calibrate seed drills, germination tests should be done on all seed lots. A seeding mortality estimate is also needed. A common value for seedling mortality -- seeds that germinate but don't develop -- is 3 percent.

Seeding the same amount of seed each year won't mean you always get the same plant population. Barley seed, for instance, can vary 25 percent in size and weight, 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 1,000-kernel weight of your own seed when calculating seed rates and calibrating seed drills.

Seeding rate:

Seeding rate is an important factor when considering all the decisions that need to be made at planting time. A high seeding rate, for instance, can result in: higher crop yields, better weed competition, earlier maturity, fewer tillers, smaller seed size and shorter plant height.

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's a good idea to have a value for the 1000-kernel weight. Otherwise, you'll need to count out 1,000 seeds and weigh them. The Postal Service has good scales. Remember that 1 ounce equals 28.3 grams. So, if you weigh 1,000 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 seeding rate calculator on the web site to get the desired seeding rate. I used the calculator to determine these rates for winter wheat:

plants/ft2  15 15 15 15
germination 95% 95%  95% 95%
seedling mortality  3% 3% 3%  3%
row-spacing  7" 7" 11"  11"
1000-kernel weight (grams) 30 40 30 40
grams of seed per 100 feet of travel 27 37 43  58
seeding rate, lb/ac 47 63 47 63

For now, if you are looking for some suggested seeding rates, here is a summary of the information contained in this web page:

Common Cereal Seeding Rates

Desired plant population     per sq. m      per sq.ft      1,000 kernel seeds per lb     weight (grams)  (avg.)
           
Wheat - hard red 250 24   30 - 40 11,000-15,000
Wheat - soft white 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
Corn -grain 6.1 0.6   380 1,200
Corn- silage 7.6 0.7   380 1,200

Special Crop Seeding Rate

Desired plant population   per sq. m     per sq. ft  1,000 kernel seeds per lb.      weight (grams)     (avg.)
           
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
Sunflower Confection 4.5 0.4   175 2,600
Sunflower Oil 6.0 0.6   126 3,600

Calibrating seeding equipment:

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). 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.

And, 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 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 are 39 and the row spacing is 7 inches, then the seeding rate is equal to:

39 grams x 12/7 = 66.8 lbs/acre