Validation of a Farmer-Friendly Soil Organic Matter Calculator.

A procedure to quantify Soil Organic Matter changes was developed by Lucas, at Michigan State University (MSU) at the request of USDA NRCS Michigan.  Lucas developed a model for Estimating Soil Organic Matter (SOM) changes based upon Plant Residue Equivalents (PRE).  Grigar developed an excel spreadsheet in 2009 (the Lucas Model 313.xml).  The Ohio State University Extension (OSUE) developed the OSUE SOM calculator from the Lucas Model 313.xml spreadsheet. (Shedekar, et. al., 2013) to help farmers evaluate the effects of various management scenarios on the dynamics of SOM in the long term.  The OSUE SOM Calculator consists of a user friendly interface to select alternative management practices to predict SOM change based on current SOM level, crop rotation, crop yields, conservation tillage, drainage, manure application type and rate, cover cropping, and residue removal rates per year.  From these inputs, the calculator uses first order decay functions as primary basis for calculating annual changes in SOM.  The OSUE SOM calculator is also capable of predicting active and passive fractions of SOM, total active nitrogen, overall soil quality generated from residue removal, percent change in SOM and corresponding amount of soil carbon sequestered or lost.  This study was conducted with an objective to validate the OSUE SOM calculator for Marlette fine sandy loam soil.

A field-scale corn erosion productivity study was conducted from 1985-2004 on research plots at the Michigan State University (MSU) Research Farm E. Lansing, Michigan to evaluate long term effects of erosion and mulch treatments on continuous corn yield and soil properties.  The major soil type was Marlette fine sandy loam, (Fine-loamy, mixed, Oxyaquic Glossudalfs) on 2%-6% slope.   A Spring Moldboard Plow disk tillage system was used with uniform management (nutrients, harvesting, etc.).  The plots were comprised of three erosion phases and two mulch treatments.  Soil organic matter, crop yield and corn residue yield were recorded from 1985-2004. The Lucas Model 313.xml and the OSUE SOM calculator were tested for predictability for each plot.  The OSUE SOM calculator was further validated for the Marlette soils using a simple split sample approach.  Preliminary statistical analysis showed that the OSUE SOM calculator based on the Lucas Model 313.xml spreadsheet performed well in predicting SOM dynamics on slight, moderate and severely eroded Marlette soils over the 20 year study.