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Corn+Soybean Digest

Avoid Wasting Fertilizer by Using Right Rates and Timing

Like most Corn Belt farmers in a 50-50 corn and soybean operation, Darrell Lewis and his son Brad from Hastings, IA, claim high input costs put more and more pressure on the bottom line. And they don't want their farm's corn-feeding fertilizer disappearing from fields before it's done its work.

With N costs tied to energy prices, price volatility means it could take a stimulus package to make a crop rotation work.

The Lewises, though, are making it mesh. With fall applications of P and K and spring N treatments on top of potential residual N levels, their corn was grown about as efficiently as possible in 2009. And it yielded like no other corn crop they'd seen.

“We farm about 850 acres each of dryland corn and soybeans,” says Brad. “We've been able to limit our inputs without hurting yields. Going from fall to spring N applications has helped. We haven't lost that N to leaching or runoff. And we feel that going from anhydrous ammonia to a liquid (urea ammonium nitrate) has improved our operational efficiency.”

The corn fertilization program begins after beans are harvested. “We put out an application of P and K,” says Brad. “We hire a ground-rig applicator to broadcast it over the top.

“We usually count on at least 40 units of N from a 40-bu. soybean yield,” Brad adds. “Then we come back in the spring with an application of about 140 lbs. of liquid (32% UAN product) injected with a liquid applicator rented from our local co-op.

“That plan helped us produce a 180+bu./acre corn crop for 2009 — phenomenal yields for us. We feel that by injecting the liquid N, we're able to get better use of the nutrients in the root system,” he says.

Fall applications of anhydrous ammonia worked in the past. But time constraints due to harvest and fighting wet weather became a problem. That and the ability to go with spring N enticed the Lewises to make the switch.

Timeliness is the key in getting all fertilizer applied. But it was something that many growers lacked last fall after the wet weather brought harvest to a crawl for many. “We were fortunate,” says Darrell. “We got our beans out in early November and corn in the bin by the middle of that month.”

The Corn Nitrogen Rate Calculator,, from Iowa State University (ISU), enables growers to gauge their corn N needs cost effectively. It helps determine the maximum return to N (MRTN), based on N prices for various fertilizer products and the price of corn.

John Sawyer, ISU agronomist and soil fertility specialist, says information can be calculated for Iowa, Indiana, Michigan, Minnesota and Ohio, three regions of Illinois and three regions based on soil types in Wisconsin.

Here is a simulated Iowa calculation for a corn following soybean rotation. With N priced at 50¢/lb., 32% UAN priced at $320/ton and corn at $4/bu., the MRTN rate is 118 lbs. of N/acre. The net return to N at that MRTN rate is about $154/acre, based on an application of 369 lbs. of 32% UAN.

ACCORDING TO THE Corn Nitrogen Rate Calculator, the same net return to N of $154 would be available for $820/ton anhydrous ammonia applied at a rate of 144 lbs./acre, $280/ton 28% UAN applied at a rate of 421 lbs./acre, $450/ton 45% urea applied at a rate of 262 lbs./acre and $210/ton 21% ammonium sulfate applied at a rate of 562 lbs./acre.

The Lewises use the calculator to help manage their application rates. “We use it as a rule of thumb, depending on soybean credits,” says Brad Lewis, so it gets down to the price of each source of N and making sure you get the most out of it.

When applicable, precision-guidance application systems can enhance fertilizer and other applications, says Tony Vyn, Purdue University agronomist.

“When we're talking about preplant-N application in the form of UAN in either no-till or strip-till systems, precision guidance allows producers to plant corn either directly on top of the fertilized bands of the soil or at a precise distance away to reduce the risk of corn or seedling injury when higher UAN rates are applied,” says Vyn.

He notes that when preplant UAN exceeds 50 lbs. actual N/acre, “it's safer to plant corn at least 4-5 in. to the side. This is another area where automatic guidance gives an advantage because it offers precisely parallel planting abilities.”

Sawyer says growers should consider the use of N inhibitors to reduce the chance of N losses. He points out that several corn N management options can assist in providing economical and environ-mental benefits to growers:

  • Be realistic in selecting N application rates.

  • Account for the crop rotation.

  • Plan for available N from manure applications.

  • Avoid fall application of N fertilizer, or wait until soil temperatures at 4 in. are at or below 50° F and cooling before injecting anhydrous ammonia.

  • Spring preplant, sidedress or preplant-sidedress split applications typically provide the least risk from loss and are preferable N application timings.

  • Sidedress or in-season application should include adequate N as a preplant or starter-N application to carry the crop until sidedressing; adjust the overall N rate for the preplant/starter N and from information gained through soil N testing or in-season corn monitoring.

  • Consider using N diagnostic tools like the LSNT and corn canopy N stress sensing to make adjustments in N rates and in monitoring of N management systems. And, account for all N applications.

Of course, soil samples should be taken to determine need for P, K or lime applications. In Iowa, samples should be taken from the surface down to 6 in. Other states can see recommendations are based on samples to 8 in.


Dry fertilizers can be offloaded directly onto the applicator in the field of application, according to the Iowa Department of Agriculture and Land Stewardship (IDALS). Bulk dry fertilizers must be stored in a totally enclosed building. Loading of fertilizer into the applicator or a tender truck must take place within the building.

Liquid fertilizer storage of volumes greater than 5,000 gal. must have secondary containment, according to IDALS. A container or a combination of containers with a volume of 5,000 gal. or less is exempt, IDALS says. Loading and unloading pads are required for those facilities with secondary containment.

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