Manure Nitrogen & See It Release Over Years
Mineralises farmyard manure
Manure releases its nitrogen slowly over several seasons, not all at once — enter the manure N applied and each year's mineralization percent to get the plant-available N in year 1, 2, 3 and the three-year total.
Enter your manure application
Next: credit 70 kg N/ha against this season's fertilizer need, then carry 24 and 10 kg/ha forward as residual credits in years 2 and 3.
Mineralization percentages depend on manure type, C:N ratio, application method and soil temperature/moisture; these are planning estimates, not a soil-test substitute.
Manure mineralization — key facts
- Year N available
- applied N × that year's %
- 3-year total
- year 1 + year 2 + year 3
- Year 1 (FYM)
- ≈ 20–35% of total N
- Year 1 (poultry)
- ≈ 50–60% of total N
- Later years
- small single-digit %
- Driven by
- warm, moist, aerated soil
- Use as
- a credit against fertilizer N
- Privacy
- Runs in your browser; nothing uploaded
Manure nitrogen is a slow drip, not a single dose
Most of the nitrogen in manure is organic and locked up until soil microbes break it down. That release is fast in the first season, then tails off as only stable humus remains, giving a declining curve over three or more years. Treat all of it as available at once and you under-fertilize the first crop while wasting the carry-over; ignore the residual and you over-apply nitrogen on a field with a long manure history. Counting each year's release fixes both.
This tool turns the manure nitrogen you applied into the plant-available N in years one, two and three and the total. Use each year's figure as a direct credit against your crop's nitrogen requirement, then buy only the fertilizer that makes up the balance. Pair it with the Fertilizer Acidification Lime and Starter Fertilizer Safety tools to round out your nutrient plan.
Credit every season
Count year 1, 2 and 3 release against fertilizer.
Stop over-applying
Value the residual nitrogen a manure history supplies.
Compare manures
See fast poultry N versus slow rotted FYM.
Budget accurately
Turn total manure N into available kilograms.
Frequently Asked Questions
How does this calculator estimate available nitrogen?+
It multiplies the manure nitrogen you applied by each year's mineralization percent. Year 1 available N = applied N × year-1 percent, and the same for years 2 and 3 using their lower percentages; the three-year total is the sum. So 100 kg of manure N at 40% / 15% / 7% releases 40, 15 and 7 kg of plant-available N across three seasons — 62 kg in total.
Why doesn't all the manure nitrogen become available at once?+
Most manure nitrogen is locked in organic compounds that soil microbes must break down (mineralise) before plants can use it. That decomposition happens gradually, fastest in the first season when the easy material breaks down and slower afterward as only the stable humus remains. The result is a declining release curve over several years rather than a single hit.
What are typical mineralization percentages?+
They vary with the manure. Fresh poultry manure may release 50–60% of its N in year one; well-rotted farmyard manure or compost often only 20–35%, with single-digit percentages in years two and three. Slurries that are mostly ammonium can be higher still in year one. Use the figures your manure analysis or local guidance suggests for the type you spread.
What is the residual or carry-over credit?+
It is the nitrogen still mineralising in the second and third seasons after application — years two and three in this tool. If you apply manure regularly, these carry-over credits overlap and add up, so a field with a long manure history supplies more background nitrogen than its single most recent application suggests. Counting the residual avoids over-applying fertilizer.
How do I use this to cut fertilizer?+
The available nitrogen the tool reports is a direct credit against your crop's nitrogen requirement. Subtract year-one available N from the recommended N rate and apply only the balance as fertilizer; in following years subtract the residual credits too. This is how manure replaces purchased nitrogen — the calculator turns the slow release into kilograms you can deduct.
Does weather and soil affect the release?+
Strongly. Mineralization is a microbial process, so it speeds up in warm, moist, well-aerated soils and slows in cold or waterlogged conditions. A hot growing season can pull more nitrogen forward; a cold spring delays it. The percentages here are season-average estimates — adjust them up in warm climates and down in cool ones for a closer match.
Is this the same as the total nitrogen in the manure?+
No. The total nitrogen is everything in the manure; the available nitrogen is only the fraction that mineralises and reaches the crop each year. Always start from the manure N applied — ideally from a manure analysis — and let the mineralization percentages convert it into the plant-available share. The rest stays as slow-building soil organic nitrogen.
Are the figures precise?+
They are solid planning figures from your inputs and chosen release rates. Real mineralization shifts with manure type, storage, application method and the weather, so treat the result as a working nitrogen budget. Confirm with soil nitrate tests or crop response where you can, and refine the percentages over a few seasons of using the same manure source.