Estimate tons of manure per acre from a nutrient need, lab manure nutrient content, and first-year availability percentage.
Use this when you have a manure analysis (lb nutrient per ton) and a crop need in lb/acre, and you want a first-pass application rate in tons/acre before talking to Extension or a certified planner.
Typical for solid or composted manure bookkeeping. Liquid slurry often uses gallons/acre — convert mass carefully or use a slurry-specific tool.
Available nutrient per ton is content times availability fraction. Rate is need divided by that available nutrient.
tons_ac = need_lb_ac ÷ (content_lb_ton × availability% ÷ 100)
field_tons = tons_ac × acres
Need 120 lb N/acre, manure 10 lb N/ton, 50% first-year available, 20 acres:
Available = 10 × 0.50 = 5 lb/ton → rate = 120 ÷ 5 = 24 tons/acre → field = 480 tons.
Assumptions: uniform manure, single nutrient focus, availability % from lab or Extension table for your manure type and timing.
Limits: ignores phosphorus index caps, setbacks, incorporation timing, and multi-year residual N. Over-applying to meet N can overload P.
Responsibility: follow nutrient management plans and local regulations.
Use your manure lab report or Cooperative Extension tables for manure type (beef, dairy, poultry) and whether it is incorporated promptly.
This page is tons/acre. For liquid, convert gallons to tons with density, or use gal/acre tools with nutrient lb/1000 gal.
Yes. Run the same math with P2O5 need and manure P content; take the more restrictive rate.