How to Estimate Nitrogen from Cover Crops

 At Prairie Creek Seed, we know the value of continually learning and sharing information. The following methodology comes from Associate Professor Julie Grossman and her team of grad students at the University of Minnesota Department of Horticulture Science. We love the way this process was put together and look forward to seeing what estimates you can all get from your cover crops!

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1.  Sample your biomass

          1.  Create a square to measure a known area

          2.  Take off the above ground growth in that area a few times throughout the field.

          3.  Dry the sample until it is crunchy and weigh it

2. Convert to biomass lbs per acre

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3. Calculate how much nitrogen is in that material using this table: 

  

Cover Crop

Examples

%N

Legumes

Hairy Vetch, Clovers, Peas

4% at flowering

3% as seeds are maturing

Non-Legume Grasses

Cereal Rye, Oats, Sudangrass

3% at flowering

2% as seeds are maturing

Non-Legume Broadleaves

Buckwheat, Radish, Turnip

Similar or less than grasses

 

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4. Estimate how much will be available in 1 year. We retain 50% of available N when residue is incorporated and 40% when unincorporated.

Incorporated

Unincorporated

Lbs N  0.50 = Lbs available in 1 Year

Lbs N  0.40 = Lbs available in 1 Year

        You can also skip the last three steps and get an estimate using our Nitrogen Calculator Tool. All you need there is your dry sample weight and area measured! Do keep in mind that these are estimates and many factors go into to N fixation and release including variety, weather, nitrogen applications, and geographical location.