Feeding wheat’s hidden hunger

For years, farmers have adopted a pretty standard approach to fertilizer use. They set a yield goal and apply enough nutrients to achieve that goal, based on recommendations from land-grant universities. That approach is dated, said Cat Salois, director of research and technology at the McGregor Company. 

Salois said many recommendations were developed 30 to 40 years ago. In that time, wheat yields in Washington have improved 75 percent; Idaho wheat yields have doubled. 

“I’m not convinced those standards are in a way calibrated to the yields and advances in breeding technology we’ve seen in the last 30 or 40 years,” she said. “Another way to think about this is, what are we trying to manage? Are we trying to push yields or achieve an ROI maximum?” 

Timing is key. From the growth stage Feekes 2 to Feekes 6, the crop demands 30 percent of that total nitrogen. From Feekes 6 to Feekes 10, the crop needs 45 percent of its total nitrogen—or 4.8 pounds of nitrogen each and every day during the peak demand curve. Plants kind of stink at retrospectively picking up nutrients,” she said. “If we miss the target, we can’t magically pick up optimum timing, we can’t pick up 14 pounds toward the end of the demand curve.” 

Kip Cullers, the Missouri soybean grower who once held the world record for soybean production per acre, used to say, “if high yields are your target, the plant can never have a bad day,” Salois said. What he’s getting at is how can we hit those demand curves to frontload that nitrogen application and will it still be there when the demand curve needs it. 

Growers are good at applying nitrogen. However, McGregor research based on more than 180 locations shows that other nutrients, properly applied at the right time, can greatly impact optimum wheat yield. These include the following: 

  • Boron—Wheat is generally considered not highly responsive to boron. However, there is a synergistic effect when timed appropriately—at flag leaf, with a strobilurin fungicide and nitrogen. Salois said 0.10 pounds of an uncomplex boron product, containing organic acid can boost wheat yield 5 bushels per acre. 
  • Potassium—From stem elongation to through flag leaf emergence, wheat uses 7 pounds of potassium each day. Meeting those crop needs boosts yield and protein. And while soils typically are high in potassium, research shows potassium is highly variable from acre to acre. Applying potassium thiosulfate at about Feekes week 5, or just before stem elongation, boosted yields 6 to 8 bushels per acre. 
  • Phosphorus—A 3-year rotation featuring 100 bushel per acre winter wheat, 40 bushel per acre spring wheat and 2,000 pounds of chickpeas per acre removes a total of 75 pounds phosphorus. As an immobile nutrient needed throughout the season, Salois advised phosphorus needs to be “layered” on, with about 40 percent applied with the seed, with the rest of it broadcast or shanked in. 
  • Zinc—70 percent of the wheat plant’s zinc update occurs in the first third of the plant’s ecological life. A well-chelated zinc source, applied in-furrow at planting, boosted yield 3.5 bushels per acre yield advantage. “The problem here in the Pacific Northwest is that not all of us are equipped with in-furrow fertility kits like we have in the Midwest,” she said. “Hitting that early season nutrient demand becomes a problem.” 

Bill Spiegel can be reached at [email protected]