The old rule of thumb about seeding 1.5 bushels of wheat per acre just doesn’t apply anymore, says a researcher with North Dakota State University.
Variety, seeding date and even latitude make a difference, Grant Mehring told the Manitoba Agronomists Conference in Winnipeg last December. He described his extensive, three-year research trials on seeding rates for several HRSW varieties planted in 23 different environments.
“Seeding rate can be far off with bushels per acre because that’s just a volume. You can have a lot of different seeds per volume or per bushel when the kernel weights are different,” Mehring said.
His research showed that using a common North Dakota seeding rate of 1.5 bu./acre of two varieties with very different kernel weights — 15 grams per 500 kernels for one and 20 grams per 500 kernels for the other — could result in a difference of up to 400,000 seeds per acre.
“People ask, ‘is it really that critical in spring wheat because it tillers nicely and will likely catch up,’” said Mehring. “That’s probably true but if your intention was to plant a seeding rate without using seeds per kilogram — the kernel weight — you are far from that. It’s important to take into account kernel weight and also germination.”
In Mehring’s trials he also counted how many seeds on average across 10,000 wheat plots over three years didn’t germinate, and saw an average of 10 per cent to 15 per cent stand loss.
“It would be good to take a 10 per cent to 20 per cent expected stand loss into consideration when you are planting spring wheat,” Mehring said. “That is what agronomists recommend in North Dakota and it is what helps growers get the plant population they want.”
Tillering is important
Environment is also going to take away some of the seeds a producer plants, added Mehring, which is why planting as early as possible in the spring is crucial to get plants established.
“As you delay planting date you need to increase seeding rates,” said Mehring, whose research showed significantly less tillering in plants that were planted a month to five weeks later than the optimum early planting date.
“Environment is a major factor in tiller production and yield, so it’s also important to choose the HRSW cultivars that are most broadly adapted to your growing region.”
Mehring’s research has clearly shown that varieties have very different tillering capacities.
“Tillering is what impacts your spikes per acre, and your spikes per acre is what gives you yield at the end,” he said. “It’s important to get the stems-per-acre numbers up to the level you need to get the yield you want but it doesn’t do any good necessarily to increase seeding rate because in our trials, when averaged over many different environments and years, overall that didn’t increase stems per acre or yield.”
Know your varieties
Increasing seeding rates can also increase the risk of lodging especially in high-lodging potential cultivars, along with other factors such as environmental conditions, taller variety height, and N fertilization.
“If you are planting a high-lodging cultivar — a cultivar that yields great and has lower straw strength — you are probably not going to want to push the seeding rate at all, because if the environment is right it’s going to lodge and there will be a harvest and yield impact,” Mehring said.
“Some varieties will tiller so well that the seeding rate doesn’t necessarily make a difference and that’s something you need to know,” he said. “If you have some agronomic information that says a variety has a higher tillering capacity, that may be one you consider scaling back a bit on the seeding rate.”
Mehring’s biggest message to producers and agronomists was to gather as much information as possible about different HRSW varieties to be able to make the best seeding rate choices for each situation.
“You should use all of the information that you know about a variety,” he said. “It’s not just the yield and the protein of the variety that matters. It’s the height of the variety, the lodging potential, the tillering capacity, relative maturity, whether you’re planting earlier or later — all of these intricate factors will be important to take into consideration when you choose a seeding rate.”
Mehring is working on using predictive tools such as known genetics, as well as phenological characteristics including tillering, plant height and photoperiod sensitivity to predict optimum seeding rates for different HRSW cultivars.