Farmer-friendly tool for predicting soil organic matter

Most farmers in the Midwest have recognized the importance of soil health (including organic matter) in crop production. They would like to know how changes in their farming practice affect soil health and crop yield.

Recently, biofuel products (cellulosic ethanol) have created a market for corn stover. This can be another source of income, but is there a “cost” in reduced soil health?

Crop residue and manure have been the main sources of soil organic matter (SOM) in agro-ecosystems. Removing corn stover or wheat straw could have the undesirable consequence of reducing soil quality. A good question is: how much crop residue can be removed without harming soil health?

The researchers at the Ohio State University’s South Centers have developed a simple SOM calculator that can help farmers answer that question. With minimal input requirements and step-by-step guidance, the calculator is designed to be “farmer-friendly.” It asks for basic information (e.g. crop rotation, tillage, soil type, SOM content from latest soil test report) as user inputs; and uses an exponential decay model to simulate decomposition of crop residue and native soil organic matter on an annual basis. The calculator can be used to validate SOM levels in the past as well as predict organic matter dynamics for up to 50 years.

The calculator is available in Microsoft Excel file format and includes a user-guide and a printable report. It consists of a user-friendly interface, with options to select crop rotation, yields, management practices (e.g. tillage, cover crops), amendments (e.g. manure and compost), and residue removal rates per year. An erosion routine allows users to estimate SOM loss by erosion. In addition to agronomic crop rotation, rotational cover crops can also be added at desired frequency. Users can specify crop residue removal rates (percent of total or pounds/acre); and get an estimate of the revenue generated from residue removal, percent change in SOM and corresponding amount of soil carbon sequestered or lost.

A “test scenario” module allows users to evaluate different options (e.g. adding cover crops, manure, changing to continuous no-till) and visualize, in seconds, their effects on the SOM and nutrient levels. The printable report also includes a graphical illustration of changes in the SOM content over time.

The SOM calculator has been successfully tested using data from long-term research trials in Michigan and Illinois. Although, it was developed for Michigan conditions, the SOM calculator will be applicable to Ohio with minor modifications.  You can learn more at the Conservation Tillage Conference, March 4, at Ada.

This work was the result of cooperation among the Corn Marketing Program of Michigan, the Soil, Water and Bioenergy program at the Ohio State University’s South Centers at Piketon, and the Dept. of Food, Agricultural and Biological Engineering at Columbus.


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  1. If you are interested in trying the calculator, you may request for a trial version from Visit the SOM calculator webpage and fill out a Non-member Request form.

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