The 4 Rs of Topdressing Wheat

Scout your wheat crop to monitor for yellowing on the lower, oldest leaves. If it looks like the younger, newer leaves are stealing nitrogen, it’s time for a boost.

Maximize yield by mastering nitrogen timing, source, method and rate

c71a029c91e343899c185e542c7226a11Whether you’re preserving winter wheat yields or thinking ahead to your spring wheat crop, take into account nitrogen needs. Topdressing with nitrogen midseason can give your wheat the extra boost it needs for top-end yields.

The keys to nitrogen efficiency include the right timing, right source, right method and right rate.

“Consider topdressing this year because a lot of the region had fall rain and any nitrogen applied preplant [winter wheat] could have leeched and might not be enough to get through the season,” says Brian Arnall, Oklahoma State Extension precision nutrient management specialist. “If you’ve lost enough nitrogen you could get protein deductions and lose test weight at the end of the season.”

The optimal time to topdress winter wheat is right around the corner. It’s important to apply nitrogen before jointing. “After jointing, when you drive over wheat you kill the growing point,” Arnall explains. “Prior to the flag leaf any nitrogen applied goes into grain yield.”

The nitrogen source often plays a role in application method. Urea and liquid UAN are the two most common forms of nitrogen used for topdressing. “Both will get nitrogen to the roots with rain,” says Romulo Lollato, Kansas State Extension wheat and forages specialist. Urea is typically applied broadcast, and UAN can be tank mixed and applied with herbicide.

While UAN might be more appealing because it can potentially cut down trips across the field, it might not be as effective in no-till. Unless you change your application method, “when UAN hits residue it can be counted as a loss,” Arnall says. He advises using streamers to concentrate UAN down into the residue.

Right rate is more difficult to advise in general terms because it depends on several factors, such as yield potential, how much nitrogen was leeched, if the field is showing signs of deficiency, field history and year.

“Optimal nitrogen rate varies year to year,” Lollato explains. “For the past few years, it’s been 66 lb. per acre. But one year it might be 90 lb. and another year 30 lb.”

“Ideally you’ll know what the nutrient profile looked like at planting if you had a soil test. You can base your rate on that,” he adds. “At $10 per soil sample and 15 to 20 minutes dedicated to pulling, a good sample is worth it.”

On average, each bushel takes 2 lb. of available nitrogen, so you can estimate what you need to finish the season strong based on your yield goal.

If you didn’t get a soil sample, scout your fields for areas with nitrogen deficiencies. “Wheat can be more challenging to scout since the leaves are smaller,” Arnall says. “Look for yellowing or chlorosis on the lowest, oldest leaves where the young leaves rob nitrogen from the older leaves.”

Yellowing on the lower leaves from tip to inner leaf indicates a nitrogen deficiency. If you see yellowing on the top new leaves, it likely indicates a sulfur deficiency. When you find large spots, it might be time for a boost of nitrogen (or sulfur), or pull a soil sample for a more precise reading.

Nitrogen is an essential nutrient that can make or break yield. “Nitrogen increases tillering, influences head size—it’s like gas to a car, you need it,” Lollato says. “Cutting back on nitrogen cuts back on yield potential. We need to make sure we use the four Rs to maximize results.”