Crop Fertility Tips

There's nothing simple about figuring out crop fertility for 2022. Examining what worked and what didn't this year, and pairing that with soil and in-season tissue testing is a good place to start.

Sulfur, potassium and phosphorus were among the top nutrients that some corn and soybeans ran short on in 2021, according to agronomists and soil fertility specialists. The nutrient deficiencies that reduced yields primarily occurred in drought-stricken areas.

In regions that received ample rain, split-applying nitrogen using a stabilizer was a boon for corn yields.

Jason Clark, South Dakota State University (SDSU) Extension soil fertility specialist, recommends farmers analyze how their 2021 nutrient plans worked and their fertilizer needs when making crop-nutrient decisions for 2022.

"Start with your soil-test values," he says. "That's what is going to help you know what to do and how to spend your money."

Sulfur:

WinField United Agronomist Tyler Steinkamp says sulfur (S) deficiency was fairly common in corn fields in 2021 and in the company's answer plots that experienced drought stress.

Sulfur shortages mostly occurred in fields that only relied on elemental sulfur or gypsum applications, as needed. Both nutrients require adequate moisture to be converted into the soluble form of sulfate to be taken up by plants. Sulfur is necessary to help corn carry out photosynthesis and efficiently use nitrogen, among other things.

"Elemental sulfur or gypsum work great, but I wouldn't rely on either for all my needs. Neither are very water soluble," Steinkamp says. "In a dry year, if elemental sulfur or gypsum are the only source of sulfur you have, plant uptake can be limited."

On average, he contends S deficiencies reduced corn yields by 10 to 12 bushels per acre (bpa) based on company yield checks.

If S is needed in 2022, Steinkamp advises farmers to apply multiple types based on need to reduce the chance of deficiencies in corn, especially if rainfall is scarce. Most of the Western Corn Belt is suffering from drought or abnormally dry conditions. DTN Ag Meteorologist John Baranick doesn't expect dry conditions to subside in the Western Corn Belt heading into spring.

The weather phenomena La Niña -- below-normal Pacific Ocean temperatures near the equator -- returned for the second year in a row in late October. That typically brings erratic periods of warm and cold weather in the winter, but not necessarily more precipitation west of the Mississippi River.

"I don't see a whole lot of change in the drought picture through the winter in the Corn Belt west of the Mississippi," Baranick says.

Applying elemental sulfur or gypsum, and a more water-soluble form of S in-season, such as ammonium sulfate or ammonium thiosulfate, can mitigate risk, Steinkamp says. He recommends a 10-to-1 ratio of nitrogen to S for high-yielding corn.

Sulfur needs of crops have steadily increased in recent years because of reduced atmospheric deposition of the nutrient, increased crop removal rates and adoption of no-till, according to Purdue University. Every 20 bushels of corn remove 1 pound of S from the soil. For more on S, visit www.agry.purdue.edu/ext/corn/news/timeless/sulfurdeficiency.pdf.

"Our group of farmers have pretty consistently put on sulfur, whether it's in the fall, spring or in-season," says Matt Hardy, agronomy division manager for North Iowa Cooperative, based in Thornton, Iowa.

He says sulfur prices climbed about 30 to 40% in 2021 compared to the previous year. Hardy says SO4 pelletized gypsum is an exception. It has only increased about 6% in price since 2020, but availability is scarce.

Many fertilizers, such as potash and anhydrous ammonia, have doubled or more during the past year, according to the DTN Fertilizer Index.

Potassium:

Drought stress exacerbated potassium (K) deficiencies in corn and soybeans, which were on the edge or below acceptable levels in many fields. Clark says the lack of K was the most talked about nutrient that limited yields in South Dakota in 2021.

For corn, Steinkamp says low K reduced yields by up to 50 to 60 bpa and caused "severe" reductions for soybeans in 2021.

"When we have a dry year, the clay particles collapse around potassium, and it gets stuck," Steinkamp adds. "The way to fix that is bump up the rate of application in the fall."

For high-yield corn and soybeans, K levels should be 200-plus parts per million (ppm) per acre, he suggests. It takes roughly 10 pounds of K (17 pounds of potash) to increase soil-test levels by 1 ppm. Potassium removal rates for 220-bpa corn and 70-bpa soybeans are 59 and 91 pounds, respectively, per acre, he adds.

Phosphorus:

Phosphorus (P) levels in ppm need to be in the upper 20s to low 30s for high-yielding corn and soybeans, Steinkamp recommends. Soybeans and corn remove 0.8 and 0.4 pounds, respectively, of P per bushel.

It takes about 20 pounds of P to increase the soil test by 1 ppm. Steinkamp says keeping nutrient levels at optimum rates is important, but high fertilizer prices could be a barrier.

"What we need to do to truly push yield is to fill as many holes in the crop nutrition program as possible," he explains. "With nutrition, you don't always know if a particular nutrient will result in higher yields, because another nutrient may be low. Building all soil nutrient levels is key.

"I would apply removal rates plus build a little," Steinkamp continues. "Hopefully, fertilizer prices will start coming down to build rates back up."

Nitrogen:

Drought wasn't an issue in 2021 for much of the Eastern Corn Belt. Tim Laatsch, director of agronomy in North America for Koch Agronomic Services and a farmer near Effingham, Illinois, says his region experienced one of the wettest Julys on record that carried over into early August.

Laatsch contends his decision to split-apply 200 pounds of UAN32 for corn with a nitrification inhibitor to minimize leaching was fortunate given the wet conditions. He applied about half preplant as a weed and feed and half injected in-season at the V3 growth stage. In some fields, the nitrogen split favored in-season application.

"The risk-mitigation strategy paid off for me big-time," Laatsch says, noting corn yields exceeded 250 bpa. "I mitigated the risk of drought affecting nutrient uptake later in the season because I got the nitrogen to the root system early. But, I hedged against a wetter season with a nitrification inhibitor that reduced nitrogen losses to make sure it was available to the crop during grain fill and the reproductive stages."

Baranick says another year of ample precipitation could be in the cards for the Eastern Corn Belt because of La Nina. Knowing that drought could return to southern Illinois, as well, Laatsch plans to employ a similar nitrogen strategy in 2022 to reduce risk.

For corn growers who only apply fall or preplant anhydrous ammonia, Laatsch says adding a nitrification inhibitor is advisable. Koch replicated field trials show an 11-bpa yield response versus nitrogen applied without a nitrification inhibitor.

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-- Follow the latest from Matthew Wilde, Crops Editor, by visiting the Production Blogs at dtnpf.com or following him on Twitter @progressivwilde

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