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KHEM Farms’ harvest outside Rosalia.
Photo by Erin Lundt

FARMER'S TOOLBOX

Wheat College precursor focuses on yield

March 2021
By Trista Crossley


Peter “Wheat Pete” Johnson made the first of two planned appearances in Eastern Washington last month to talk about the building blocks of yield potential. His “visit” was part of the Agricultural Marketing and Management’s 2021 schedule

Johnson is the resident agronomist with Real Agriculture, where he hosts a weekly podcast, “Wheat Pete’s Word.” He is also a regular on “Agronomy Monday” on Real Ag radio, Sirius Satellite Radio 147, and he owns a small farm in Ontario, Canada.

Although the January visit was virtual, Johnson will be the featured speaker at this year’s Wheat College, currently scheduled as an in-person event on June 15 in Ritzville, Wash. Johnson called the January session a “precursor” to Wheat College.

“Some of what we are going to talk about today will be a little bit back to the basics, because that’s what the building blocks of yield really are,” he said. “You give four or five growers the same weather, the same soil, the same inputs, and 27 percent of the final yield comes down to the grower and their ability to time things right and know how to do things differently. To me, that’s what makes the building blocks of yield so interesting.”

Johnson defined cereal yield components as the number of heads per square foot; the number of spikelets or head size; the number of grains per spikelet; and the weight of each grain. In the January session, he focused on the following factors that help determine the number of heads per square foot.

Genetics. According to Johnson, picking the right genetics is worth at least a 20 percent difference in yield.

Seeding starts with the combine. Specifically, growers need to spread harvest residue as evenly as possible to help ensure a uniform crop.

“It (residue) affects soil temperature, soil moisture, drill performance, early crop growth and potash. Most of the potash is in the straw rather than the grain,” he said, adding that a potash deficiency can develop in areas that don’t get enough residue.

Seeding date. The earlier you seed, the higher yield you get. Johnson explained every day a farmer delays planting means a corresponding decrease in yield. He said wheat plants need 180 growing degree days (GDD) from emergence to producing one leaf and one tiller. For wheat planted in mid-September, that means it will generally take six days to get to that point. For wheat planted in mid-October, it will generally take 18 days to get to the same point.

“For yield, the risk of seeding too early is far less than the risk of seeding too late. You’ve got to play with it,” he said.

Seeding rate. This goes hand in hand with seeding date and how well the plants have established themselves.

“You are never going to be a high yield wheat grower if you aren’t looking at actual population,” Johnson said. “Seeding rate comes back to tillering. When you plant early, you’ll get more tillers per plant. We have to do a better job of accounting for those tillers because it makes such a big difference in our head count.”

According to studies, early-seeded wheat tends to get taller, so Johnson recommended that if growers move up their planting date, they need to consider reducing their seeding rate, otherwise, “you’ll have all sorts of lodging problems.”

Stand. “We want about 60 viable stems per square foot. If you can get in that range, you are probably in good shape for high yields,” Johnson said. For dryland growers in low rainfall areas, they may need to back that number off to about 40 stems.

Planting depth. Johnson advised growers to make sure they are planting their wheat at least an inch deep, so the crown forms at three quarters of an inch from the surface.

“The reason the crown forms at three quarters of an inch is the coleoptile, when it sees light, that’s when it initiates the formation of the crown,” he explained. “There’s no point in seeding deeper, especially if you seed early, unless you need to go to moisture. All you do by seeding deeper is delay emergence. That means you don’t have as many growing degree days to make tillers.”

However, getting to moisture trumps that advice.

Johnson also advised spending some time with the planter to try to increase the planting uniformity in both seed depth and distance. He pointed to a new study that showed a 10 percent yield increase when the stand is uniform.

“If seeds aren’t planted at the same depth, how do we expect uniformity?” he asked.

Row width. Yield tends to come down when wheat is planted in wide rows.

“It’s all about light interception,” Johnson said. “When light hits bare dirt, you are losing yield. Full stop. When you intercept it with a leaf, you are making yield.”

In dry climates with wider rows, he advised looking for a variety with a pendulum leaf that can arch out and intercept the light. In narrow row situations, look for a variety that is more upright so it won’t shade neighboring plants.

Weed control. Johnson said he is a huge believer in fall weed control. A dense canopy also helps with weed control.

Crop rotation. “If you grow wheat on wheat, you just gave up an average of 17 percent on yield,” he said.

Phosphorus. Wheat is a huge phosphorus user, and if growers don’t replace what is being taken off, it doesn’t matter what else they do.

They won’t achieve a high yield. “Invest in the soil, because if you invest in the soil in terms of maintaining a medium level of fertility, the interest from that investment will pay you back for years and years to come,” he said.

Johnson closed out his presentation by answering questions from growers. More than 90 people attended the session.