Pilot states: IA · IL · MN · WI · NEMarketplace for seed, equipment & inputs — not just organicOrganic-first tools, because almost no one else builds themTrial data: 18 land-grant universitiesNext release: seed browse · June 2026Backed by Soil Health ExchangeAlways free for farmers · vendors pay 5% on completed salesNo listing fee · no RFP-response fee · no ads · everPilot states: IA · IL · MN · WI · NEMarketplace for seed, equipment & inputs — not just organicOrganic-first tools, because almost no one else builds themTrial data: 18 land-grant universitiesNext release: seed browse · June 2026Backed by Soil Health ExchangeAlways free for farmers · vendors pay 5% on completed salesNo listing fee · no RFP-response fee · no ads · ever
Tool · Nitrogen · updated with a field-credit synthesis

Cover-Crop Nitrogen Credit Calculator.

Static tables blur together three different things: total N in the residue, potential first-season mineralization, and the fertilizer-rate change you can actually act on. This version keeps those pieces separate: residue N, immobilization risk, cover-crop credit or debit, and the adjusted N plan for the following crop.

Suggested fertilizer adjustment

-74lb N / acre

120 lb/ac planned → 46 lb/ac suggested

Cover crop credit is about 74 lb N/ac. Your current plan can drop from 120 to roughly 46 lb/ac; verify with PSNT or an in-season sidedress check.

Moderate

Cover-crop credit/debit

+74 lb/ac

range 48 to 100 lb/ac

▸Reference band for this species and placement: 35 to 90 lb N/ac. The model caps the upper end and only allows negative debits where the band supports them.

▸This tool credits aboveground shoots only. Root N is treated as zero first-season fertilizer replacement unless measured separately.

▸Planned fertilizer N does not change residue mineralization. It is used only to show the adjusted rate after the cover-crop credit or debit.

▸Biomass and tissue N are estimated, so treat the range as more important than the single point estimate.

What I’d do in the field

Practical next steps

Moderate
Fertilizer plan

Use 46 lb/ac as the planning rate, or stay in the 20 to 72 lb/ac range if you want to be conservative.

Before buying N

Measure biomass and tissue N if this recommendation changes a real purchase. Defaults are good for planning, not for a final nutrient budget.

Best fit

Legume-heavy stands are most useful when the following crop needs N soon after termination. Keep the stand growing into bud or early bloom when field timing allows.

Net N release window · 18 weeks post-termination

Net N Gross PAN Tie-up Planting
wk 0wk 4wk 8wk 12wk 16wk 18+740lb N / ac
Gross first-season PAN71
Estimated plant-available N released from aboveground residue before timing limits or immobilization debit.
Immobilization debit0
Temporary N tie-up risk from high-C:N or low-N residue. This is why mature grasses can be a debit before corn.
Estimated residue C:N13:1
Blends the species stage proxy with tissue N using the screening relationship C:N ≈ 40 / N% when residue carbon is near 40% of dry matter.
Aboveground shoot N143
This is the residue N pool in the shoots, not the same thing as a next-crop fertilizer credit.
Reference band35 to 90
Extension-style first-season range for this species group and placement. Use the low side when inputs are estimated.
Adjusted N plan46
Your planned rate after applying the cover-crop credit or debit. Confirm with PSNT, crop sensors, or a sidedress check.
Field sampling tip. Clip a known area before termination, weigh fresh biomass, dry a subsample to estimate dry matter, and send a tissue sample for total N when the credit will affect a real fertilizer purchase. Defaults are only planning placeholders.
Model basis. The credit follows a practical Extension-style structure: shoot N pool × residue quality × placement × weather × crop-demand timing, minus an immobilization term for high-C:N residue. It is a planning tool, not a substitute for PSNT, sidedress sensing, or a certified nutrient management plan.
Methodology

How this calculator works.

Shoot N is not the same as fertilizer credit. The calculator starts with aboveground biomass × tissue N to estimate the residue N pool, then converts only part of that into first-season plant-available N. Roots are treated conservatively at zero unless separately measured, because first-year root PAN is too uncertain to credit aggressively.
Residue quality drives the conversion. Tissue N and C:N are screened together using the field shortcut C:N ≈ 40 / N%. High-quality legumes can release a large share of shoot N in year one; mature grasses often immobilize soil N instead.
Placement and synchrony matter. Incorporated residue gets the highest first-season multiplier. Surface mulch, roller-crimping, and planting green all push the tool toward the lower half of published credit ranges because release is slower and more timing-sensitive.
The next crop still decides the usable credit. Credits stay largest before corn and other high-N-demand crops, shrink when demand is delayed, and go to zero before soybean or other legume cash crops. Your planned fertilizer rate is used only after the credit is calculated, so the tool can show a suggested adjusted N plan.
What it does not model. Wisconsin-style manure-credit rules for rye after manure. Multi-year soil-N carryover. Full organic compliance planning. Direct allelopathy penalties. Local height-to-biomass calibrations. Use PSNT or sidedress checks in-season, especially when grasses or brassicas put the estimate near zero.