Worksheet for Calculating Biosolids Application Rates in Agriculture

Dan Sullivan and Craig Cogger
Oregon State University and Washington State University-Puyallup

Overview

This bulletin will walk you through the calculations that yield the biosolids agronomic rate. This rate is based on biosolids quality (determined by analytical results), site and crop nitrogen requirements, and regulatory limits for trace element application. In almost all cases, nitrogen controls the biosolids application rate. By calculating the agronomic rate, managers can match the plant-available N supplied by biosolids to crop N needs.

The calculations consist of 6 steps:

1. Collect information on the site and crop, including crop N requirement.
2. Estimate the plant-available N needed from the biosolids application.
3. Collect biosolids nutrient data.
4. Estimate plant-available N per dry ton of biosolids.
5. Calculate the agronomic biosolids application rate on a dry ton basis.
6. Convert the application rate to an "as is" basis.

This bulletin consists of:

• A worksheet with instructions for completing the application rate calculations.
• The same calculations in equation form for those who prefer using equations.
• Tables for calculating trace element loading.

To learn more about the use and management of biosolids as a fertilizer, refer to Fertilizing with Biosolids, PNW publication 508, which is the companion to this bulletin.

The agronomic rate calculation presented here is based only on nitrogen. We recommend monitoring of soil test phosphorus levels at biosolids application sites. See these OSU Extension publications (available at http://eesc.orst.edu/) for assistance with agronomic soil tests for phosphorus:

• Soil Test Interpretation Guide (EC 1478)
• A List of Analytical Laboratories Serving Oregon (EM 8677)
• Fertilizing with Biosolids (PNW 508)

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Worksheet for Calculating Biosolids Application Rates in Agriculture, PNW 511-W
by Dan Sullivan and Craig Cogger
(Oregon State University and Washington State University-Puyallup)
March 1, 2000