‘N’-formation, please: Answering the tough fertilizer questions this spring


COLUMBUS – How much corn to plant this spring is going to be a tough decision for Ohio and Indiana farmers facing either shortages or extremely high prices for nitrogen fertilizers, a key input.

Nitrogen fertilizer prices have more than doubled since last year because of huge natural gas price increases. Worse yet, nitrogen isn’t available at all in many areas of the Midwest.

The situation portends a huge shift from corn to soybean acres, which could push up corn prices and lower bean prices.

But there’s no need to panic and automatically switch corn acreage to soybeans, says Ohio State University agricultural economist Allen Lines and Purdue University Extension agronomist Sylvie Brouder.

A farmer can position himself to take advantage of expected increases in corn prices if he can still get respectable yields with reduced nitrogen applications, Lines said.

An important factor is knowing where the soil’s fertility needs are in relation to the hypothetical yield response curve for nitrogen, Lines said. The curve flattens out when corn yield response no longer increases with additional nitrogen applications.

Farmers may be able to get by with less nitrogen and not hurt yields. Or they may be able to cut down on nitrogen – and yield – and still remain within respectable profit margins, Lines said.

“As a general rule, most farmers are used to putting nitrogen on to maximize the yield of corn,” Lines said. “Can we bring down the amount of nitrogen without damaging the corn yield?”

Lines offers this sequence of general scenarios to consider when making planting intentions for this spring:

* If a farmer has a full supply of nitrogen: “There’s probably little reason to switch from corn to soybeans,” Lines said. “There is a potential here for corn prices to rise from where they are, and you can take advantage of that.”

* If a farmer can get a full supply of nitrogen, but at a high price: Consider putting on less nitrogen fertilizer because additional yields are going to cost plenty in terms of the expense.

“If you have a full supply of nitrogen at a high cost, consider reducing nitrogen by 10 percent to 15 percent. That will probably put you in a more profitable position.”

* A farmer has, or can get, only 80 percent of the normal supply of nitrogen for the farm: Reduce nitrogen applications over all corn acres to 80 percent, but still plant your intended corn acreage.

* A farmer can get only 50 percent to 75 percent of normal nitrogen supply: Apply nitrogen at an 80 percent rate, and plant remaining fields in soybeans.

* A farmer has no nitrogen fertilizer: The only choice is to plant soybeans or an alternative crop. However, be sure to lock in a government marketing loan rate to protect profitability.

Purdue’s Brouder said cutting back a few pounds on the amount of nitrogen applied per acre should mean minimal yield losses. “Given the way corn responds to fertilizer nitrogen and that recommended rates are conservative, cutting back nitrogen rates by 10 percent from the recommended rate is unlikely to hurt yields by more than a few bushels per acre,” Brouder said.

Brouder’s “N prescription” includes evaluating a field’s yield goal; taking an nitrogen credit and adjusting the rate per acre; reducing nitrogen rates when sidedressing; using a pre-sidedress nitrate test on organic soils or soils that have a history of manure or other organic material application; understanding the key behavior differences among nitrogen fertilizers; and resisting the impulse to “top-off” rates with extra nitrogen.

In evaluating yield goal, consider setting a goal equal to the field’s five-year corn yield average, Brouder said.

In addition to productivity potential, Purdue recommendations use an nitrogen credit system to account for other sources of nitrogen available from previous crops or applied wastes that will reduce the amount of fertilizer nitrogen needed, she said.

Brouder recommends nitrogen credits for common previous crops of 30 pounds per acre for soybeans or an annual legume cover crop, 40 pounds per acre for grass sod or pasture and up to 140 pounds per acre for an established forage legume.

If you switch sources. While corn plants don’t care where the nitrogen comes from, there are big differences among fertilizers in how they act in soil, Brouder said.

“If you are accustomed to using anhydrous ammonia and find that anhydrous supply restrictions will force you to substitute a different fertilizer source for some of your applications, you should carefully check all calculations to make sure you are applying the right fertilizer rate to achieve your target total nitrogen application,” she said.

Another question to ask is whether a farmer can afford to break a field out of its regular crop rotation, Lines said.

Planting a continuous crop of soybeans could risk disease problems or an insect build-up that could be more costly in the long run, he said.

Nationally, farmers have already indicated that a massive shift to soybeans could be in the offing, Lines said. Farmers planted 2 million fewer acres of winter wheat, for the lowest acreage in 30 years.


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