Last year’s wet weather resulted in a lot of lost nitrogen, which resulted in corn yields being less than their potential.

Nitrogen losses were considerably greater with fall applied N vs spring applied. In a test plot in Linn County in 2008, corn that received 135 lb/A of N (without a nitrification inhibitor) yielded 65 bu/A more with a spring application of anhydrous ammonia vs. the fall application. A nitrification inhibitor applied with the fall applied anhydrous resulted in a yield increase of 20 bu/A, but still yielded 45 bu/A less than the spring applied anhydrous. The nitrification inhibitor had no affect on corn yield when applied with the anhydrous in the spring. This year much more nitrogen will be spring applied because of the late fall and high fall nitrogen prices, which should hopefully reduce nitrogen losses even if we have another wet spring. Although much nitrogen has already been applied, some are still making decisions about nitrogen applications this spring.

With the sky high N prices, it is tempting to cut back on nitrogen rates. Optimum nitrogen rates do decline as nitrogen prices increase, but of course corn prices have also increased. The corn nitrogen rate calculator can help producers see how corn and N prices affect optimum N rates. The calculator at uses research results from over 250 trials across Iowa in determining optimum N rates. According to the calculator, with $850/T anhydrous and $4 corn, an average recommendation for corn on soybean ground is 116 lb/A, compared to 123 lb/A with $350/T anhydrous and $2 corn.

Some producers are planning to apply urea this year for the first time because of lower urea prices compared to anhydrous. All nitrogen sources can be equally effective when correctly applied, but there are some special considerations when using urea for the first time. Urea can be lost through volatilization when it is left on the surface, so is best incorporated if a rain doesn’t due the incorporation within a few days. Losses are greatest when it is applied to wet soils with warm temperatures, especially on high pH soils. Another complaint I sometimes hear with urea is about spread pattern problems. Uneven spread patterns with P & K may not show up dramatically in the appearance of the corn, but uneven spread with nitrogen can lead to streaks in the corn and some yield losses. Doing some extra calibration with the spreader can pay off.

SOURCE: ISU’s Jim Fawcett