Most crop production experts recommend a soil test before planting corn. That’s not enough for Ed Winkle.

The Martinsville, OH, grower and no-till disciple takes nitrogen (N) and other nutrient management practices to the max – and depends on a leaf-tissue test to determine the fertilizer prescription he’ll use before planting.

Even with higher corn prices, input costs can still nix big profit potential. But by making sure mid-season N applications are first needed, then on target, growers can hopefully boost yields without blowing the fertilizer budget, says Gyles Randall, University of Minnesota soil scientist emeritus.

“It depends on where you farm and whether you plant corn after soybeans or corn after corn,” says Randall. “There are a lot of differences in soils. Some areas (like the eastern Corn Belt) need more N than we do. One needs to use the diagnostic application available for each particular situation.”

The end-of-season cornstalk test can help get a jump on knowing your N needs for the following year’s crop. But Randall says it likely won’t provide accurate data for in-season tests. “There’s just too much going on within the plant to determine how much N is needed,” he says.

Winkle grows corn, soybeans, wheat and barley. “For corn, I typically make mid-season applications on the later ‘racehorse’ hybrids,” says Winkle, who pushes for 190-200 bu./acre. “For the early workhorse hybrids, we usually receive the N we need from applications at planting.”

His region has clay loam (heavier soils) that can prevent nutrients from moving freely through the root system. “I have 40 years of soil history,” he says, “and it can still be a stab in the dark. I feel comfortable with the nutrient levels that work for me and use the tissue test to get an accurate indication where I stand at preplant and mid-season.”

The mid-season leaf tissue test involves taking samples from the highest leaf near the plant’s production areas in mid-June. Cost is about $20-25/sample. “I take at least one sample per acre and send it off to Midwest Laboratories in Omaha, NE,” he says. “They melt it down into ash and examine it. Based on 100 years of records, they can tell me what the nutrient level is for N, P (phosphorus), K (potassium) or 17-18 other nutrients in all.”

Winkle plants 30-in. rows with plant populations of 28,000-32,000 plants for later hybrids and 36,000-40,000 for early ones. The early season plants usually receive their entire N application at planting, based off tissue samples from the previous year and late-year soil samples. “We plant these hybrids on poorer soil, so we plant thicker,” says Winkle. “They like the N up front and normally go with a 28% N liquid-fertilizer application.”

For the later hybrids, he normally applies mid-season 28% N. “On the later racehorse hybrids, I’ll often go with one-third of the N at planting, one-third when herbicide is put down and one-third with a sidedress,” he says. “I’ll also use a half-at-planting and half-at-sidedress program.”

Randall says that in some years when heavy rainfall occurs, a mid-season N application works well, provided there was a sufficient preplant application. And when the climate is more forgiving, preplants work well.

He says that with corn following soybeans, mid-season applications “are a little more problematic because we have a difficult time assessing the need for N. When we try to analyze the plant, which is getting a lot of N from the soil, it doesn’t allow us to really diagnose what’s going on. Later on, the plant may show N problems. But when it gets to the first of July, it’s often too late for mid-season applications under non-irrigated conditions.

“If it’s corn after corn, then in-season diagnostics can be helpful,” Randall says. “We’ve found that 60 lbs. preplant and 80-100 lbs. in-season can work. We just need enough N up front to get us to mid-season.”

Soil types are important. Randall says plant-diagnostic systems, like GreenSeeker or Crop Circle, can be beneficial. “If a farmer is faced with soils ranging from well drained to very well drained, in-season applications will have a much better way of paying for themselves,” he says.

Peter Thomison, Ohio State University soil scientist, says that from the eight-leaf stage through tasseling, N uptake is 4-8 lbs./day. “For most corn hybrids, N uptake is complete shortly after pollination,” he says.

“So, most of the N should be applied prior to the 10-leaf stage, with any supplemental applications complete by or shortly after tasseling. If corn has gotten too tall to sidedress by mid- to late June, it has probably not been severely stressed,” Thomison says.

Winkle uses a 12-row toolbar configuration to apply N. “I like the full toolbar, with a disk opener and a drag chain to put a little soil over it to keep all the N we can,” he says. “That can help prevent the need for an N stabilizer.”

Ammonia or N solutions knifed in are usually preferred, especially in high-residue fields, says Thomison. “Granular urea can also be applied over the top in clean-tilled situations, but those applications can be risky if rainfall does not come shortly after application,” he says.

“Urea stabilizers should be considered in high-residue situations. Granular urea broadcast will cause some foliar burn when granules fall into the whorl. While it may appear unsightly, little yield decrease normally occurs if the fertilizer is applied before the 10-leaf stage,” he says.

Winkle concludes that N applications aren’t an exact science. “I am flexible to any point of N and will pay more when I need it, like any other farmer would,” he says. “My goal is to plant when I think the soil and weather is right, not by the calendar.”

 

N calculators are valuable tools

With the price of nitrogen (N) as volatile as corn prices, knowing your N input costs is more than essential. Online N calculators and budget estimators on university websites can help budget N inputs and application rates.

“I look at them closely,” says Ed Winkle, Martinsville, OH, grower who locked in fertilizer at prices two-thirds of what they were in early March. At that time, UAN 28% was priced at 65¢/lb., about the same as UAN 32%, according to some Corn Belt cooperatives. Along with those jaw-dropping prices, anhydrous ammonia (82% N), was about 45¢/lb., while urea 45% was around 55¢/lb.

Winkle pushes for 190-200 bu., so savings for applications of about 200 lbs. N/acre add up quickly at 20¢/lb. And if half the N applied in midseason can boost yields 10 bu./acre, that’s an added $60/acre for corn priced at $6/bu.

Using the Ohio State University crop production budget Excel spreadsheet, applying 200 lbs. of 28% N to generate a 200-bu. yield would produce an N cost of about $137/acre at the 65¢ cost. Drop that price to 40¢ and the cost drops to about $90/acre.

Iowa State University’s popular N calculator (http://extension.agron.iastate.edu/soilfertility/nrate.aspx) enables users to gauge their N cost over much of the Corn Belt.

In early March, the Ohio site using a $7/bu. price for continuous corn showed these readings for using UAN 28% N: a maximum return to N (MRTN) rate of 200 lbs. N/acre (about 700 lbs./acre applied); a profitable N rate range of 189-212 lbs.; a $467/acre net return to N at MRTN; a 99% of maximum yield at MRTN; and an overall N cost for the MRTN rate of $130/acre.

That compared to about $130/acre for 625 lbs. of UAN 32% applied, $114 for 460 lbs. of urea 45 and $98/acre for 266 lbs. of anhydrous.