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Ignoring Manure, Legume Nitrogen Credits Will Be Expensive The Year

Nitrogen prices are skyrocketing and 2001 corn prices will probably be no better than last year”s — not a great situation for corn growers. One easy way to save money on nitrogen this year is to take full credit for the nitrogen that”s already in your fields, according to Larry Bundy, a soil scientist at the UW-Madison”s College of Agricultural and Life Sciences.

In a recent analysis of Wisconsin corn-growing trials, Bundy found that taking credits for the nitrogen content of manure applications and legume crops grown in the previous three years was consistently more profitable than ignoring the credits.

Bundy analyzed data from nitrogen response trials at more than 100 sites with a variety of cropping histories. The trials were conducted on a wide range of soil types at research stations and private farms throughout southern and central Wisconsin. He used results from each trial to analyze the economics of full crediting versus no crediting of manure/legume nitrogen.

He found that, compared with ignoring nitrogen credits, adjusting for organic nitrogen inputs increased gross returns $8/acre to $17/acre for the entire database, and up to $30/acre under the most favorable production conditions. Lower corn prices and/or higher nitrogen prices make crediting even more lucrative, Bundy says.

Basing manure nitrogen credits on a manure analysis is best, Bundy says. Book values are averages, and your farm”s values may differ somewhat from the average. But crediting from either analysis results or book values is going to pay off, he says. To see book values for crediting manure and legume nitrogen in Adobe Acrobat format, go here or get publication A3340, Corn Fertilization, at your county UW Extension office.

The pre-sidedress soil nitrate test, or PSNT, will give you a more accurate picture of your soil”s nitrogen status. (The state soils labs at Madison and Marshfield and several certified private soil-testing labs in Wisconsin can run the test.)

In the first year after a forage legume or manure application, returns were higher where credits were based on book values, compared with PSNT results. Using PSNT values provided better returns on soils with one- to three-year histories of manure/legume additions, Bundy found. Returns from fully crediting N from organic sources using either book values or the PSNT increase with lower corn prices and/or higher nitrogen prices, he adds.

Besides saving money, proper nitrogen crediting can help reduce nitrogen losses to the environment, Bundy notes. Too much nitrogen on fields can lead to high nitrate levels in local groundwater, and researchers believe that agricultural nitrogen runoff into the Mississippi River is largely responsible for the hypoxic “dead zone” in the Gulf of Mexico. The zone, more than 5,000 square miles of water, contains too little oxygen to support fish, shrimp and other aquatic life.

In short, ignoring nitrogen credits doesn”t pay. “The frequently stated reason for inadequate nitrogen crediting is that farmers fear economic loss due to nitrogen deficiencies if recommended optimum nitrogen rates are used,” Bundy says. “However, the data from these trials show that it was profitable to make those adjustments and take those credits.”

Some growers who have credited manure nitrogen and reduced their rates of commercial nitrogen have noticed pale-colored emerging corn that appears nitrogen-deficient. A cool spring will slow the release of manure nitrogen. Corn plants may appear yellow at first, but nitrogen release will increase as temperatures rise, and the growing corn will respond to the flush of nitrogen, Bundy says.