October 10, 2023

Don’t Forget Your Nitrogen Credit

Chris Augustin – Director, Dickinson Research Extension Center 701-456-1103 Chris.augustin@ndsu.edu

As your planning next year’s fertility paired with soil sampling don’t forget your nitrogen credit. A nitrogen credit accounts for the active carbon/nitrogen pool in your soil. This active pool is made up of plant residues, proteins, worm casts, and other soil organic matter that will convert or rather mineralize organic nitrogen during the subsequent growing season into readily plant available nitrate. We call this a nitrogen credit as a nitrogen soil test tests for nitrate. The soil nitrate test doesn’t account for the organic nitrogen pool. So depending on the previous crop or tillage system, we estimate that a certain amount of nitrate will be mineralized and we can reduce nitrogen fertilizer inputs. NDSU recommends a 40 lbs nitrogen/ac credit for legume crops like soybean, field pea, lentil, and edible beans. Forages like alfalfa and sweet clover are a little different and depend on the plant density and growing seasons post termination. There are nitrogen credits for sugar beets which is dependent on top color. The long-term no-till nitrogen credit is dependent on the crop, but ranges from 20 to 50 lbs nitrate/ac. For more info on the nitrogen credit amounts refer to North Dakota Fertilizer Recommendation Table and Equation. https://www.ndsu.edu/fileadmin/soils.del/pdfs/North_Dakota_Fertilizer_Recommendation_Tables_and_Equations_SF882.pdf The nitrogen credit doesn’t come from the rhizobia that fix nitrogen. Rather, the environment following the legumes or no-till environments make an excellent habitat for the Nitrosomas and Nitrobacter bacteria that mineralize the organic nitrogen pools and render plant available nitrate. The legumes leave little residue which increase soil oxygen exchange and allows the soil to warm a bit faster. These factors lead to an increase in soil biological activity. Additionally, the no-till soil is much more biologically active than a conventional tilled system which encourages more nitrogen mineralization. I’ve had studies across the state over a variety of climatic conditions. When analyzing the data, I can key out that nitrogen credit. Still, the number one way to manage nitrogen inputs is to soil test. Pair with agronomic fertilizer recommendations and nitrogen credits when applicable can help you maximize your inputs.

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