Cover Crop Nitrogen Credit Calculator

Quantify the nitrogen fixation value from legume cover crops. Enter your species, biomass, and termination timing to calculate your real dollar credit toward next year's N budget.

Cover Crop Species

Biomass (dry matter)3,000 lb/acre

1,000 lb (sparse)8,000 lb (dense)

At 3,000 lb/acre, Hairy Vetch fixes ~105.0 lbs N/acre total (3.5% N concentration)

Inoculant Used?

Yes — adds 30% bonus to N fixation efficiency

Inoculant bonus: 15.8 additional lbs N/acre available to next crop

Termination Timing

Anhydrous Ammonia Price$861/ton

$700/ton$1,100/ton

Cost per lb N: $0.53/lb ($861/ton ÷ 2,000 lb ÷ 0.82 N content)

Acres with Cover Crop

Available N Credit to Next Crop

68.3

lbs N/acre available after all adjustments

Dollar Value / Acre

$35.83

Total Farm Value

$17,916

500 acres

N Credit Calculation Breakdown

Total N Fixed

3,000 lb biomass × 3.5% N concentration

105.0 lbs/acre

Availability Factor

Only ~50% of fixed N is available to the next crop; remainder ties up in organic matter

50%

Timing Adjustment

4+ weeks before planting

100%

Inoculant Bonus

Rhizobia inoculant improves nodulation efficiency by ~30%

+30%

Available N Credit

105.0 × 50% × 100% × 130%

68.3 lbs/acre

N Value vs. Anhydrous Cost ($/acre)

N Credit Value$35.83/acre

68.3 lbs × $0.53/lb

Anhydrous to Replace It$35.83/acre

What you would pay to apply same N as anhydrous

Seed + establishment cost: typically $25–45/acre. At $35.83/acre in N credit, you are covering seed cost and capturing additional soil health benefits.

N availability estimate based on University of Wisconsin and Penn State Extension cover crop N credit guidelines. Actual results vary by soil type, organic matter, moisture, and termination method. Always tissue-test your cover crop for precise N concentration.

Maximizing Cover Crop N Credit

Termination Timing is Everything

Terminating 4+ weeks before planting allows full mineralization and decomposition. Late termination can tie up N or cause allelopathy issues — and cuts your available credit by 60%.

Inoculant Pays for Itself

A $3–5/acre inoculant investment adds a 30% bonus to N fixation. On a 3,000 lb biomass hairy vetch stand, that is 15+ additional available lbs N/acre — worth $10–15 in anhydrous savings.

Biomass is the Multiplier

Every additional 1,000 lb of dry matter biomass adds 15–38 lbs more fixed N depending on species. Focus on seeding rate, seeding date, and winter hardiness to maximize biomass at termination.