Fertilizer per acre calculator
To apply 137 lb of nitrogen per acre with urea, which is 46-0-0, you spread 297.8 lb of product per acre — the same rate is 333.8 kg/ha. That nitrogen rate sits inside the 127 to 147 lb N/ac range Iowa State's MRTN calculator gives for corn following soybean, a recommendation rather than a legal ceiling: the United States has no federal per-acre nitrogen limit. Save a field above and the same answer arrives as total product, whole bags and what is left in the last one.
Your answer
Product to spread470.6 lb/ac
- N delivered
- 160 lb/ac
- P₂O₅ delivered
- 0 lb/ac
- K₂O delivered
- 0 lb/ac
- The same rate in kg/ha
- 527.5 kg/ha
Field job sheet
What this means for the field in front of you:
Limit check: Outside the recommended range 127–147 lb N/ac: this case applies 160 lb N/ac (Iowa State University Corn Nitrogen Rate Calculator (MRTN), corn following soybean — a recommendation, not law, Iowa, MRTN 137 lb N/ac at corn $6.50/bu and anhydrous ammonia $1,400/ton, checked 2026-09-22). A recommendation, not law.
How the answer is worked out
Fertiliser arithmetic is one division and two conversions, and getting it wrong is expensive in both directions — an under-applied field loses yield, an over-applied one loses the fertiliser and, where a ceiling applies, the compliance too.
- Product rate = nutrient rate ÷ the nutrient’s share of the product. Straight urea is 46 % N, so every pound of nitrogen needs 2.174 lb of product.
- What the pass actually delivers = product rate × each of the three percentages. A 15-15-15 blend spread at a nitrogen rate delivers the same weight of phosphate and potash whether you wanted them or not.
- The metric twin = 1 lb/ac is 1.1209 kg/ha, converted once at the end.
The rate unit is part of the answer
A rate written “160” means nothing on its own; the page carries lb/ac and kg/ha as first-class units and prints both, because a product label, an agronomist’s recommendation and a spreader manual do not always agree on which one they are using. The copy button gives the unrounded figure for a spreadsheet.
The limit check, and what silence means
Where the edition’s market has a sourced figure, the result is measured against it and the clause is named. This edition has no law to name, so it prints the state extension recommendation band instead and labels it as a recommendation. Either way the page shows the figure your case was measured against and where it comes from — never a table of limits or rates to copy from, because a number lifted out of its context is how a wrong rate travels.
And the other direction is worth saying plainly: no limit line is not an all-clear. State nutrient management rules, manure application restrictions, setbacks from water and permit conditions all exist under a federal silence.
A worked example
Every figure below is computed by the calculator above from this case — nothing here is typed in by hand:
- What do you know?
- The nutrient rate I want
- Type of fertiliser
- Mineral fertiliser
- Nutrient
- N
- Rate
- 137
- Rate unit
- lb/ac
- N in the product
- 46
- P₂O₅ in the product
- 0
- K₂O in the product
- 0
- Bag size
- 50
- Price per unit of product
- 0.38
Product to spread:297.8 lb/ac
- N delivered
- 137 lb/ac
- P₂O₅ delivered
- 0 lb/ac
- K₂O delivered
- 0 lb/ac
- The same rate in kg/ha
- 333.8 kg/ha
Limit check: Within the recommended range 127–147 lb N/ac: this case applies 137 lb N/ac (Iowa State University Corn Nitrogen Rate Calculator (MRTN), corn following soybean — a recommendation, not law, Iowa, MRTN 137 lb N/ac at corn $6.50/bu and anhydrous ammonia $1,400/ton, checked 2026-09-22). A recommendation, not law.
Worked by Agrimetra with the same engine the calculator above runs.
What this means in the United States
There is no federal per-acre nitrogen ceiling in the United States; nitrogen is managed through state programmes and land-grant extension recommendations instead, and several states require a written nutrient management plan rather than capping a rate. This page therefore prints a recommendation range, labelled as a recommendation, never as law.
Questions growers actually ask
- How does a bag analysis become a product rate?
- The three numbers on the bag are percentages of N, P₂O₅ and K₂O by weight. Divide the nutrient rate you want by that percentage and you have the product rate: 137 lb of N from a 46 % nitrogen fertiliser is 137 ÷ 0.46, which is 297.8 lb of urea per acre. The other two nutrients come along for the ride and are printed as what the same pass delivers.
- Why does the page ask whether the fertiliser is mineral or manure?
- Because the legal ceilings that exist — the EU Nitrates Directive limit of 170 kg N/ha in Germany, Poland and France — apply to nitrogen from manure, slurry and digestate, not to mineral nitrogen. Checking a urea rate against that ceiling would print a verdict the clause does not support, in either direction. In this edition the question changes nothing legally, because the United States has no federal limit at all.
- Is the 127 to 147 lb range a rule I have to follow?
- No. It is the Maximum Return to Nitrogen band from Iowa State's calculator for corn following soybean at one price pair, and the page says so on the result. It is an economic recommendation for Iowa, not law and not a guarantee for another state, another rotation or another price of nitrogen. Several states do require a written nutrient management plan instead of capping a rate — check your own state's programme.
- What if I know the product rate and want the nutrients?
- Switch the first question to "the product rate I plan to spread" and the calculation runs the other way: it prints the N, P₂O₅ and K₂O that rate delivers, which is how you check whether a blend someone has quoted you actually covers the crop.
Last updated:
Sources
- Iowa State University — Corn Nitrogen Rate Calculator (MRTN) (checked September 22, 2026)
- Iowa State University — Integrated Crop Management, nutrient management (checked September 22, 2026)