When developing your manure nutrient management plan, getting a good sample and receiving your manure test results is only the first step. After you get your test results, you need to ensure that the units (pounds, gallons, etc.) in the report match the units that are used in your plan. When they do not match, how can you make the conversions?
Note: Phosphorus is used in these examples, but the calculations are the same for all nutrients.
Converting Dry Matter to “As-Is”
There are two formulas for converting manure analyses results from % dry-weight (% dwt) or ppm to “as-is” results. One is used when your analysis is expressed in lb/ton and the other is for lb/1000 gal.
| lb/ton as sampled = (% Solids/100) x (% Analysis dwt/1001) x 2000 lb/ton |
| lb/1000 gal = (% Solids/100) x (% Analysis dwt/1001) x (density2 lb/gal x 1000) |
1For results in ppm replace 100 with 1,000,000
2To do this the density of the manure must be known. Liquid manure density can vary from 8-9 lb/gal, but will typically have a density around 8.3 to 8.5 lb/gal. Manure density can be easily estimated with a 5 gallon bucket and a set of scales. See estimating manure density.
Examples
A. Manure Analysis: 10.5% solids, 1.4% P dwt
(10.5% solids/100) x (1.4% P/100) x 2000 = 2.9 lb P/ton
B. Manure Analysis: 10.5% solids, 14,000 ppm P dwt, Manure density 8.3 lb/gal
(10.5% solids/100) x (14,000 ppm P/1,000,000) x (8.3 lb/gal x 1000 gal) = 12.2 lb P/1000 gal
Converting Manure Analysis Results From Elemental to Oxide
Standard Conversion Factors: P x 2.3 = P2O5; K x 1.2 = K2O
Examples
A. Manure Analysis: 2.9 lb P/ton
2.9 lb P/ton x 2.3 = 6.7 lb P2O5/ton
B. Manure Analysis: 12.2 lb P/1000 gal
12.2 lb P/1000 gal x 2.3 = 28.1 lb P2O5/1000 gal
Converting Manure Analysis Results from Liquid to Solid Or Solid to Liquid
To do this the density of the manure must be known. Liquid manure density usually varies from 8-9 lb/gal. Manure density can be easily estimated with a 5 gallon bucket and a set of scales. Liquid manures typically have a density around 8.3 to 8.5 lb/gal. Estimating Manure Density.
lb/ton = lb/1000 gal ÷ (density lb/gal x 1000) x 2000 lb/ton
OR
lb/1000gal = lb/ton x (density lb/gal x 1000) ÷ 2000
Examples
A. Manure Analysis: 28.1 lb P2O5 /1000 gal , Manure density estimated at 8.3 lb/gal
28.1 lb P2O5 /1000 gal ÷ (8.3 lb/gal x 1000) x 2000 = 6.7 lb P2O5 /ton
B. Manure Analysis: 6.7 lb P2O5 /ton , Manure density estimated at 8.3 lb/gal
6.7 lb P2O5 /ton x (8.3 lb/gal x 1000) ÷ 2000 = 28.1 lb P2O5 /1000 gal
Related Manure Testing Web Pages
- Overview of Manure Testing
- Step 1. Manure Sampling
- Step 2. Manure Test Results
- Step 3. Total and Available Nutrients
- Common Manure Test Results Conversions (you are here)
- Step 4. Manure Test Record Keeping
Authors: Doug Beegle, Pennsylvania State University and John Peters, University of Wisconsin