Manure Application Rate Calculator
The manure application rate calculator tells you how many tons of manure to spread on each acre to meet a crop's nutrient need, so you fertilise to the agronomic target rather than guessing. The method is the standard nutrient-balance relationship used in every nutrient management plan: the application rate equals the nutrient needed per acre divided by the plant-available nutrient content of the manure. Because only part of the nitrogen, phosphorus or potassium in manure is available to the crop in the first season, you size the rate on the available nutrient reported by a manure analysis, not the total. Spreading to this rate supplies enough nutrient for a realistic yield goal while avoiding the over-application that runs off into waterways and wastes a valuable resource. Enter your own target nutrient per acre and the nutrient content of your manure to plan a spreading rate, compare manures of different strengths, or check a contractor's recommendation against your own numbers. Every figure here is computed deterministically from the formula shown in full below, with a worked example that reconciles exactly to the calculator so you can follow each step and trust the result rather than guessing at a spreading rate.
The application rate equals the nutrient needed divided by the manure's nutrient content: rate = nutrient need / nutrient content. To supply 150 lb of nitrogen per acre from manure carrying 10 lb of available nitrogen per ton, spread 15.00 tons/acre. Richer manure lowers the rate.
Manure application rate formula
Rate (tons/acre) = N / C
N = nutrient needed per acre, in pounds
C = available nutrient per ton of manure, in pounds
The nutrient need comes from a yield goal and soil test. The nutrient content comes from a manure analysis and should be the plant-available amount. Dividing need by content gives the tons of manure to spread on each acre.
Worked example
A crop needs 150 pounds of nitrogen per acre. The manure analysis reports 10 pounds of available nitrogen per ton.
- Nutrient needed = 150 lb/acre
- Available nutrient = 10 lb/ton
- Rate = 150 / 10 = 15 tons/acre
The application rate is 15.00 tons per acre. These are the calculator's default inputs, so the result above matches the widget exactly.
Rate at different manure strengths
Tons per acre to supply 150 pounds of nitrogen at a range of manure contents.
| Need (lb/acre) | Content (lb/ton) | Rate (tons/acre) |
|---|---|---|
| 150 | 5 | 30.00 |
| 150 | 10 | 15.00 |
| 150 | 15 | 10.00 |
| 150 | 20 | 7.50 |
Land, water and resource data: US Geological Survey (USGS).
Manure application rate calculator: frequently asked questions
What is a manure application rate?
A manure application rate is how much manure to spread on each acre to supply a target amount of a nutrient, usually nitrogen, phosphorus or potassium. It is found by dividing the crop's nutrient need per acre by the nutrient content of the manure. Matching the rate to crop need avoids both under-fertilising and over-applying, which can run off into water.
How do I calculate the application rate?
Divide the nutrient needed per acre by the nutrient content of the manure. If a crop needs 150 pounds of nitrogen per acre and the manure supplies 10 pounds of available nitrogen per ton, the rate is 15 tons per acre. Make sure the need and the content use the same nutrient and the same units of weight.
Should I use total or available nutrient?
Use the plant-available nutrient, not the total nutrient in the manure. Only part of the nitrogen in manure is available to the crop in the first season; the rest is tied up in organic matter and released slowly. A laboratory manure analysis reports both total and estimated available nutrient. Sizing the rate on available nutrient prevents over-application.
Why match the rate to crop need?
Applying more nutrient than the crop can use is wasteful and risks loss to leaching and runoff, which degrades water quality. Applying too little limits yield. A nutrient management plan sets the target nutrient per acre from a realistic yield goal and soil test, and the application rate converts that target into tons of manure per acre.
Does this account for multiple nutrients?
No. This calculator sizes the rate to a single target nutrient. Manure supplies nitrogen, phosphorus and potassium in fixed proportions, so a rate set to meet nitrogen need may over- or under-supply phosphorus and potassium. Many plans size manure to the most limiting nutrient and make up any shortfall with a supplemental fertiliser.
Official sources
- Land, water and natural resource data: US Geological Survey (USGS). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.