Nitrogen credits: what the last crop and the manure already gave your corn
I pulled the credit tables out of UW Extension A2809 so you can type in a field history and get the pounds of N to take off the corn rate. Every number below is from that book, with its edition and date next to it. Nothing here is a guess of mine.
Pick a field history and, if you spread manure, the manure. The answer fills in here.
How to use the answer
Take the corn nitrogen rate for your soil and last crop, then subtract this total. The corn rate table in A2809 (Table 6.1) says to subtract these credits where corn follows a forage legume, a legume vegetable or a green manure crop, or where manure has been spread. For soybean before corn there is nothing to subtract, because the corn rate for that row was worked out from corn after soybean. Use first-year available N from manure, not the total N in the load.
Where a green manure range is given, the calculator shows both ends and counts the one A2809 names for your seeding date. For vetch over 12 inches A2809 names no end, so it counts the low end and says so. Where A2809 prints no number for your case, the calculator says so instead of filling one in.
The tables behind it
| Stand, first year | Loam over 8 in | Loam under 8 in | Sand over 8 in | Sand under 8 in |
|---|---|---|---|---|
| Alfalfa, good (over 4 plants/ft²) | 190 | 150 | 140 | 100 |
| Alfalfa, fair (1.5 to 4 plants/ft²) | 160 | 120 | 110 | 70 |
| Alfalfa, poor (under 1.5 plants/ft²) | 130 | 90 | 80 | 40 |
| Vetch | 160 | 90 | 110 | 40 |
Table 9.4, lb N per acre to subtract from the corn rate, first year, by regrowth height at plow-down or kill. Red clover and birdsfoot trefoil: 80% of the alfalfa figure for a like stand. Second year after a good or fair stand: 50 lb on medium and fine soils, none on sands. UW Extension A2809 (Laboski and Peters), edition R-11-2012, the copy UW posted in March 2026 (read Oct 16, 2026).
| Green manure | Under 6 in of growth | Over 6 in of growth |
|---|---|---|
| Alfalfa | 40 | 60 to 100 |
| Red clover | 40 | 50 to 80 |
| Sweet clover | 40 | 80 to 120 |
| Vetch | 40 | 40 to 90 |
Table 9.5, lb N per acre. For the top of a range, use spring seedings plowed down the next spring; for the bottom, fall seedings. Vetch with more than 12 in of top growth before tillage: 110 to 160 lb. UW Extension A2809 (Laboski and Peters), edition R-11-2012, the copy UW posted in March 2026 (read Oct 16, 2026).
| Previous crop | Medium and fine soils | Sandy soils |
|---|---|---|
| Soybean | 20 | 0 |
| Pea, snap bean, lima bean or dry bean | 20 | 0 |
Table 9.6, lb N per acre to credit to the crop after, but never for corn or wheat after soybean: the corn-after-soybean rows in the corn rate table already count it. UW Extension A2809 (Laboski and Peters), edition R-11-2012, the copy UW posted in March 2026 (read Oct 16, 2026).
| Manure | Over 72 h or not worked in | 1 to 72 h | Under 1 h or injected |
|---|---|---|---|
| Beef, liquid | 30% | 40% | 50% |
| Beef, solid | 25% | 30% | 35% |
| Dairy, liquid or slurry | 30% | 40% | 50% |
| Dairy, semi-solid or solid | 25% | 30% | 35% |
| Goat | 25% | 30% | 35% |
| Horse | 25% | 30% | 35% |
| Poultry | 50% | 55% | 60% |
| Sheep | 25% | 30% | 35% |
| Swine | 40% | 50% | 65% |
| Veal calf | 30% | 40% | 50% |
Table 9.1, percent of the total N available the year it is applied, by time to incorporation. Second year: 10% of the total for every kind. Third year: 5%. Phosphate and potash: 80% the first year, no later credit. UW Extension A2809 (Laboski and Peters), edition R-11-2012, the copy UW posted in March 2026 (read Oct 16, 2026).
| Manure (units shown) | Total N | First-year N, over 72 h | 1-72 h | Under 1 h |
|---|---|---|---|---|
| Beef (solid) lb per ton | 13 | 3 | 4 | 5 |
| Dairy: semi-solid (11.1–20.0% DM) lb per ton | 8 | 2 | 2 | 3 |
| Dairy: solid (> 20.0% DM) lb per ton | 9 | 2 | 3 | 3 |
| Goat (solid) lb per ton | 13 | 3 | 4 | 5 |
| Horse lb per ton | 10 | 2 | 3 | 4 |
| Poultry: chicken lb per ton | 49 | 24 | 27 | 29 |
| Poultry: duck lb per ton | 12 | 6 | 7 | 7 |
| Poultry: turkey lb per ton | 51 | 26 | 28 | 31 |
| Sheep lb per ton | 19 | 5 | 6 | 7 |
| Swine (solid) lb per ton | 18 | 7 | 9 | 12 |
| Beef (liquid) lb per 1,000 gal | 16 | 5 | 6 | 8 |
| Dairy: liquid (< 4.0% DM) lb per 1,000 gal | 14 | 4 | 6 | 7 |
| Dairy: slurry (4.1–11.0% DM) lb per 1,000 gal | 24 | 7 | 10 | 12 |
| Goat (liquid) lb per 1,000 gal | 17 | 4 | 5 | 6 |
| Poultry (liquid) lb per 1,000 gal | 12 | 6 | 7 | 7 |
| Swine: finish (indoor pit) lb per 1,000 gal | 43 | 17 | 22 | 28 |
| Swine: finish (outdoor pit) lb per 1,000 gal | 18 | 7 | 9 | 12 |
| Swine: (farrow-nursery, indoor pit) lb per 1,000 gal | 21 | 8 | 10 | 14 |
| Veal calf lb per 1,000 gal | 9 | 3 | 4 | 4 |
Tables 9.2 and 9.3: total N in typical Wisconsin manure (tested 1998 to 2012) and the pounds of that N available the first year, by time to incorporation. Book values are averages; a manure test of your own beats them. UW Extension A2809 (Laboski and Peters), edition R-11-2012, the copy UW posted in March 2026 (read Oct 16, 2026).
Which edition this is
These are the credit tables as they stand in A2809 edition R-11-2012 (copyright 2012), the copy UW posted on its Crops and Soils site in March 2026, which I read on Oct 16, 2026. UW says it updated its nitrogen, phosphorus and potassium recommendations for corn and soybeans in 2026 and is moving A2809 online (UW Crops and Soils, Updates to A2809, read Oct 18, 2026). UW's online Nitrogen Crediting chapter, which I read on Nov 13, 2026, says "Coming soon!" under Manure, Legumes and Soil Nitrate Tests, so there is no newer credit table to compare these against yet. When UW posts one and it differs, this page changes and says so. Nutrient management plans in Wisconsin were still written against the 2012 document when I last read UW on it.
Questions
How much nitrogen does alfalfa give the corn after it?
UW Extension A2809 Table 9.4 gives a good alfalfa stand, with more than 8 inches of regrowth on a medium or fine soil, a first-year credit of 190 lb N per acre. A fair stand is 160 and a poor stand 130. With under 8 inches of regrowth it is 150, 120 and 90. On sands the credits are 140, 110 and 80 over 8 inches and 100, 70 and 40 under. The credit comes off the corn rate. Second year, after a good or fair stand, it is 50 lb on medium and fine soils and none on sands. This is the 2012 edition, as UW posted it in March 2026.
Do I take a nitrogen credit for soybeans before corn?
No. A2809 says not to take a soybean credit when corn or wheat follows, because the corn rate table already counts the effect of soybean. Soybean and bean credits of 20 lb N per acre apply only to other crops, and not on sands (Table 9.6).
How much of the nitrogen in manure counts the first year?
It depends on the animal and on how soon the manure is worked in. For solid dairy manure it is 25% of the total N if it sits on top or stays 72 hours or more, 30% if worked in within 1 to 72 hours, 35% if worked in within the hour or injected. Liquid dairy is 30, 40 and 50%. Poultry is 50, 55 and 60%, and swine 40, 50 and 65%. Second year is 10% of the total and third year 5%. (A2809 Table 9.1, 2012 edition.)
What does the A2809 worked example come to?
It spreads 15 tons per acre of solid dairy manure this year without working it in, and 20 tons last year the same way. This year 9 lb of N a ton times 25% times 15 tons is 34 lb. Last year 9 lb times 10% times 20 tons is 18 lb. Together 52 lb of N per acre to subtract. The calculator above gives the same answer for the same inputs.
Is this the new A2809?
No. These are the credit tables in the 2012 edition (R-11-2012), which is the copy UW posted in March 2026. UW has said it updated its N, P and K recommendations for corn and soybeans in 2026 and moved A2809 online. The UW online Nitrogen Crediting chapter said "Coming soon!" for manure and legumes when I read it on Nov 13, 2026, so these are the only published credit tables I could check. If UW posts new ones and they differ, this page changes.
Related
Credits are agronomic estimates for a typical field. A pre-sidedress nitrate test can confirm a legume credit, and a manure test beats a book value. Something here that looks wrong: tell me.