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Thousand kernel weight

Still seeding “a bushel and a half” per acre? Try moving to 1,000 kernel 
weight calculation for more precise seeding rates

Every spring Prairie farmers wait to head to the field to begin spring seeding. The drill is ready to go, and the seed is loaded. The seeding equipment heading to the field has likely been updated from 20 years ago, but has the amount of seed needed calculation also been updated?

What’s in a bushel?

“We’ve seeded a bushel and a half an acre forever and ever,” says Greg Gerry, a farmer and agronomist. “What’s in a bushel and a half?”

If you walk into Gerry’s office at Precision Ag Services near Griffin, Saskatchewan, he will be happy to explain 1,000 kernel weight for calculating seeding rates, as he feels it is an efficient way to calculate bushels needed for seeding.

What is 1,000 kernel weight? 1,000 kernel weight is the weight in grams of 1,000 seeds. It will vary with seed size — this will cause variation in the number of plants produced by a pound or bushel of seed.

The desired plant population is the number of live plants growing per square foot in a seeded field. Desired plant populations have been determined during many years of trials and research. Desired plant population can be affected by crop type, growing conditions, region, and end use of the crop. Fields with lower plant populations may compensate by increasing branches or tillers, and growing larger heads or flowers producing larger sized kernels. Fields with higher plant populations may be more competitive with weeds, however, the size of kernels produced may be reduced.

Seed survival rate must also be taken into account when calculating seeding rates. Seed survival rate includes germination, 1,000 kernel weight, and mortality rate of seedlings that germinate, but do not survive to become plants.

Gerry reminds farmers buying seed to ask their dealers for the germination percentage and the 1,000 kernel weight. If a farmer is not purchasing seed from a dealer, she must test for germination and weigh 1,000 kernels for herself.

The mortality is more difficult to calculate. Each year is different, as is each field. Factors that influence mortality include disease, insects, seeding depth and weather conditions. Cereal crops typically range from five to 20 per cent mortality. Canola crops typically range from 30-60 per cent mortality.

Calculating seeding rates

Calculating seeding rates to achieve the desired plant population with the following steps:

1. Select a desired plant population. Information on desired plant populations for all varieties can be found at www.precisionag.com, or www.agric.gov.ab.ca (search for “seeding rates”).

2. Count out 1,000 seeds and weigh them in grams, or use the 1,000 kernel weight given by your seed dealer.

3. Estimate the seedling survival rate. (Germination minus seedling mortality)

4. Calculate the seeding rate in pounds for acre or kilograms per hectare.

“By not using 1,000 kernel weight to calculate seeding rates, guys are leaving money on the table,” says Gerry, “Seed only what you need to seed. The bushel and a half doesn’t cut it anymore.” †

The calculation:

To calculate the seeding rate using the 1,000 kernel weight use the following steps.

1. Multiply the desired plant population per square foot by the 1,000 kernel weight in grams.

2. Divide that by the seedling survival rate (in decimal form).

3. Divide by 10 to get pounds per acre.

An example:

Let’s use barley as an example:

1. Multiply desired plant population (30 plants per square foot) x the 1,000 kernel weight (31g) = 930

2. Divide by the seeding survival rate (0.91) = 1,022

3. Divide by 10 = 102 pounds per acre.

Using this calculation to seed 150 acres of barley, 15,300 pounds of seed would be required. For feed barley, at 48 bushels per pound, this would mean 319 bushels of seed.

To find seeding rate charts, and more information on 1,000 kernel weight, go to www.precisionag.com, or to Alberta Agriculture Food and Rural Development (at www.agric.gov.ab.ca, just type “1000” into the search box). †

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