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| It depends on the land's crop history and the corn variety. In 1989 I bought a farm and did a soil test and it came in with 1/4% organic matter. I planted alfalfa with an oats nurse crop for several years. Then I started a 6 year rotation with the farm broken into 6 patches so each year of the rotation sequence was present. Alfalfa with oats nurse crop for the first year, then two years of alfalfa production, then one year corn, one year soy beans, and one year corn. I sold lots of baled alfalfa and decent corn and bean crops without any added nitrogen other than 100 pounds of MAP each spring for the corn crops. 11 pounds of N from the MAP and dependent on the N from the alfalfa. There was an ISU extension bulletin or ISU research in the library that showed no effect on the corn crop from adding N after two years of good alfalfa production.
Sometime later I quit growing and harvesting alfalfa and went to whole farm rotation strictly soy beans and corn and went notill. In 2007 I shopped hard for a corn variety that was efficient on its use of nutrients and found a Crow's number. I forgot the number today, but I have posted about it on this forum many times in recent years. I had organic matter up to 8 to 12% and the previous year the bean crop was probably about 48 bushels per acre. I applied 60 pounds of N in 32% 2-1/4" off the rows with the planter while planting the corn, and side dressed by dribbling every other row with 40 pounds of N as 32% when the corn was 3 or 4 feet tall. Harvested 173.2 bushels of corn dried at the elevator from 111 pounds of applied nitrogen. 0.64 pounds of N per bushel. I have seen one claim of similar production with a cover crop. With the late side dressing my corn had bright green lower leaves in August while the neighboring fields based on fall applined NH3 had brown lower leaves. I did a late season stalk test and the N tested very low at 350 ppm. The stalks were marginal but survived until harvest.
The next year I raised beans then rented the place 50/50 crop share to a strip tiller. He applied 200 pounds of N before planting and it took him three years corn on corn to beat my 173.2. His best yield has been 207 since then.
The corn number from Crows hasn't been identified by the local Channel seed dealer as a Channel number.
Gerald J.
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Nitrogen requirement for corn
