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Should you cut nitrogen on corn?

Nitrogen fertilizer prices are higher this year, but soil scientist Peter Scharf urges farmers to think twice — and push a pencil — before making drastic changes in their corn planting plans for spring.

With the prospect of higher production costs, some farmers plan to reduce their nitrogen application on corn. Others are thinking of switching from corn to soybeans. Neither action may be wise, economically, says the University of Missouri Extension specialist.

“Nitrogen costs are likely to run $10 to $30 per acre higher this year for the same rate as last year,” Scharf said. “This may reduce the profits in corn production.

“However, if enough acres are switched, corn will be in short supply and prices will rise. Beans, if more acres are planted, will be in surplus and prices will continue to drop.

“Grain prices are at least as important as nitrogen prices, in making the decision to switch acreage from corn to soybeans” Scharf said.

“When corn is planted, figure costs and returns, before cutting nitrogen fertilizer rates. Even with a doubling of nitrogen prices that we've seen, corn yield is so responsive to nitrogen that cutting back rates by more than 10 to 20 pounds per acre is probably not justified.”

The first step, before applying nitrogen, is to know how much is needed to make a crop. Soil tests can reveal the level of fertility in the soil.

Scharf, and fellow MU soil scientist John Lory, monitored 44 cornfields across Missouri for three years. In 30 fields with no major organic source of nitrogen from manure or alfalfa, they found the optimum nitrogen rates ranged from zero to 300 pounds of nitrogen per acre.

“The needed nitrogen was fairly evenly spread over that range,” he added. “There is a lot of variability out there in terms of how much is needed on each field.”

Scharf and Lory found that optimum returns to nitrogen, when 30 experiments were combined, peaked at about 140 pounds when corn was $2 per bushel and nitrogen was 20 cents a pound.

When nitrogen costs double to 40 cents per pound, the return per acre to nitrogen went down $20 and the optimum application rate dropped to120 pounds per acre.

The calculation of when additional nitrogen costs outweigh the income from additional yield depends upon the prices of both nitrogen and corn.

The advantage of switching from corn to soybeans, is that beans are legumes and fix free nitrogen from the air.

The higher costs for nitrogen have come from a shortage of natural gas. A colder-than-usual winter and scaled-back production by fertilizer plants has crimped supplies.

Scharf said that other nitrogen-needy grain crops, such as wheat and milo, should be cut back no more than 10 to 20 pounds per acre. They both respond well to fertilizer.

The MU Food and Agricultural Policy Research Institute (FAPRI) has projected season average prices for this coming marketing year at $2.05 per bushel for corn and $4.53 for soybeans.

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