How TKW (Thousand Kernel Weight) Can Affect Your Seeding Rate
One 60 pound bushel of wheat can produce about 42 pounds of flour. With this flour, you could make approximately 60 loaves of bread or enough pasta to eat a single serving every day for just shy of a year (not that you’d want to). I don’t think I could eat just a single serving of pasta but just like serving sizes, not every bushel is the same.
Many of us had the misfortune of experiencing the dry conditions of the 2021 growing season and as a result, we have seen a decrease in seed size among all crops that we have processed so far this year. We measure the TKW (Thousand Kernel Weight) for all of our cereals and peas as well as the seed size (seeds/lb) of soybeans to help us determine seeding rates. Due to the lack of moisture, the crops couldn’t fill out nearly as much as they have in the past and we have seen a decrease in the TKW of wheat, oats, and peas range from 13-22% compared to crops processed in 2020.
It’s still common to hear that wheat is seeded at 2 bu/ac or peas are seeded at 3 bu/ac but depending on the TKW you may actually be over or under seeding if you base your rate purely on a bushel quantity. As we are seeing smaller seed this year as a whole, seeding based on a bushel quantity alone could lead to a higher-than-normal plant stand and increased competition in the field. Using wheat as an example and targeting 32 live plants per square foot, if you had a TKW of 30.0g you would be seeding at approximately 104 lbs/ac. If you were to seed at 2 bu/ac (120 lb/ac) you could end up with 36-38 live plants per acre.
Another important aspect to look at, especially coming off a dry year like 2021 is the germination rates of your seed. Dry conditions leading up to, and during harvest of soybeans and peas can lead to challenges in maintaining high germination rates so it is important to be aware of the germination percentage of the seed lots you are picking up and how that might affect your seeding rate to achieve your desired plant population. To achieve a desired live plant population of 8 pea plants per square foot, you would need to seed an additional 30 lbs/ac if your lot had a germ of 85% compared to a lot with 99% germ (TKW and Mortality being equal).
We encourage any and all questions on the TKW and germination rates of the seed lots that you are picking up and together, we can come up with the best seeding rate for your operation based on your target plant population. Spring is getting closer every day and I look forward to seeing you as you come through the yard for seed pick-ups.
-Thomas Cuddy