Talk to almost any agronomist, and a lot of farmers, and they will tell you that they calculate seeding rates using 1,000-kernel weights (TKW) and target plant populations. They don’t use some arbitrary and antiquated volume measure. Why aren’t all farmers using this strategy?
“The root of the reason, I believe, is there’s not enough research,” says Steve Larocque, owner of Beyond Agronomy in central Alberta. Sarah Foster, president and senior seed analyst at 20/20 Seed Labs also believes that relatively few farmers calculate seeding rate using this method. “When I poll a room during a presentation and ask, very few are really aware of this practice, and I try to raise awareness at every talk I do. It’s just starting to become a conversation.”
The ultimate goal of calculating a seeding rate from TKW is to put enough seeds into the ground to give a targeted plant population. Germination and vigour also need to be known and are used in the calculation, as is a seed mortality estimate and row spacing.
Thousand kernel weight
TKW is the weight in grams of 1,000 kernels of seed. TKW can vary between crops and classes of cereals, and it will vary within the same variety depending on the field it was grown, the environmental conditions experienced in a particular season and year over year. “Even a small difference in TKW will make a big difference in seeding rate, depending on the crop,” explains Foster. “And getting the TKW from the lab is a quick and easy test to have done.”
TKW will vary between crops, obviously, but also between classes in the same crop, between varieties in a class and even within a variety depending on where and when it was grown.
2013 data from 20/20 Seed Labs shows that canola TKW will range anywhere from 1.04 grams to 6.07 grams. In Saskatchewan, 20/20’s data has wheat TKWs ranging from 33.66 to 48.46 grams. In southern Alberta the TKW range for wheat is 26.59 to 50.84, but take a look at a single class like durum in southern Alberta this year, the TKW ranges from 41.04 grams to 48.86 grams.
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And within varieties there is variability. Tracy Court of Court Seeds at Plumas, Manitoba shared their farm data. In 2012, Canada Western Red Spring wheat varieties Carberry and Glenn had TKWs of 35.0 and 30.2 grams respectively, and in 2013 those same TKWs were 37.7 and 34.0 grams respectively. “This year we are seeing large seed size and very big 1,000 kernel weights across all crop types and varieties,” says Court. “Producers will definitely need to seed a little heavier this spring.”
After TKW is determined, the next most important variable to know is the target plant population you are aiming for. This will vary by crop, by region and even by the intended end-use, but there are usually general guidelines that work from. Dan Owen is the agronomy manager at Hudye Soil Services who operate in Norquay, Kamsack and Sturgis, Saskatchewan. “We seed everything using TKW and I encourage all my customers to seed that way as well,” says Owen. “For our own cereal research plots, I target about 36 plants per square foot versus a lot of guys who target only 26-30 plants per square foot.” Owen prefers the higher plant populations because he sees less tillering, a bigger main head which increases yield, even maturity and a thicker crop canopy with improved weed suppression.
“We are pushing crops aggressively for yield here, so we are also pushing plant populations. I preach more main heads equals more yield, and management strategies to support that higher yield also need to be in place.” At some point, if plant populations are too high lodging and increased disease incidence will become issues.
Seed germination testing is critically important to the calculation. An allowance must also be made for seedling mortality which can occur for any number of reasons including disease, insect damage, fertilizer burn in the seed row, being seeded too deep, etc.
Seeding rate calculators are available on all three provincial government websites with complete instructions on their use. The Alberta calculator, in particular, is very use-friendly. Just pick a crop from a pull-down menu, plug in the numbers for TKW, germination, etc., and a seeding rate in pounds per acre is automatically calculated for you.
“Using bushels per acre to determine seeding rate can leave you with a thin plant stand, excess tillering, delayed maturity and a reduction in yield,” says Larocque. “On the flip side, you could be seeding heavier than you need to and increase the changes of lodging from heavy plant populations and really just wasting money on seed that doesn’t need to be planted.”