Soil Amendment Calculator
Calculate organic matter amendment rates to improve soil health. Includes manure, compost, biochar, and gypsum.
Results
Visualization
How It Works
Soil amendments improve physical, chemical, or biological properties of soil. Organic amendments (manure, compost) add nutrients and organic matter. Gypsum improves soil structure in high-sodium soils. Building organic matter by 1% requires roughly 25 tons of compost per acre.
The Formula
Nutrients Applied = Rate (tons/acre) × Nutrient Content (lbs/ton)
First-year N availability: manure 40-50%, compost 10-15%, poultry litter 60%
First-year N availability: manure 40-50%, compost 10-15%, poultry litter 60%
Variables
- Rate — Tons of amendment per acre (varies by type and nutrient goal)
- N availability — Only a fraction of organic N is plant-available in year one
- OM% — Percentage of organic matter in the amendment
Example
Dairy manure at 15 tons/acre: supplies 150 lbs N (60 available), 60 lbs P₂O₅, 120 lbs K₂O. Cost: $12/ton = $180/acre.
Tips
- Manure is a fertilizer — account for nutrients applied to avoid over-application.
- Phosphorus from manure builds up faster than nitrogen — watch soil P levels.
- Biochar is expensive but persists for centuries and improves water holding capacity.
- Apply manure based on P limits, not N needs, in environmentally sensitive areas.