Manure Application Calculator: How Much Manure to Spread
Manure is a great soil feeder, but it varies enormously in strength, and only part of its nitrogen becomes available in the first year. Spreading by eye can easily mean too little to matter or so much that it leaches.
Runs in your browser. Nothing you enter is stored.
What this calculator does
Choose a manure, enter the nitrogen your crops need and your area. The calculator gives the weight and volume to spread, the even layer it makes and the wheelbarrow loads.
How to use the manure application calculator
- Enter the area of the bed or plot.
- Choose a manure type to load typical nitrogen and density, or enter values from an analysis.
- Set the available nitrogen your crop needs.
- Enter your wheelbarrow size.
- Spread aged or composted manure and fork it in a few weeks before planting.
How the calculation works
N needed = crop rate × area manure = N needed ÷ (N content × first-season availability) volume = manure weight ÷ bulk density loads = ceil(volume ÷ wheelbarrow size)
Only a share of manure nitrogen is released in the first season; the rest feeds the soil over later years.
Worked example
A 20 m² plot needing 10 g/m² of available nitrogen takes about 133 kg of aged cow manure (0.5% N, 30% available): 0.22 m³, about three 80 L wheelbarrow loads, roughly a 1.1 cm layer.
Assumptions and limitations
- Manure analysis varies with animal, bedding, age and storage.
- Never use fresh manure on growing food crops; aged or composted manure is safer.
- Repeated heavy manuring can build up phosphorus. Test soil every few years.
Frequently asked questions
How much manure should I put on my garden?
A layer of about 2–5 cm (1–2 in) of aged manure is typical for vegetable beds, but strength varies. Use the nitrogen your crops need as the guide.
Which manure is strongest?
Poultry manure is far richer in nitrogen than cow or horse manure, so you need much less of it.
Can I use fresh manure?
Fresh manure can burn plants and may carry pathogens. Compost it or let it age for at least six months before using it on food crops.
When should I spread manure?
In autumn on empty beds, or a few weeks before planting in spring if it is well rotted.