Organic Matter

When determining the lime requitement for Carolina Bays or soils with organic matter content greater than 10%, the target pH value should be between 5.0 and 5.5. Most field crops in the southern U.S. are grown on soils with less than 2% organi c matter but if you suspect that a soil is unusually high in organic matter, you may want to have it tested by the Ag Service lab to see if the organic matter content is above 10%.

Many times organic gardeners will send soil samples to the Ag Service Lab and request the test for percent organic matter. Probably, many of these gardeners have been adding organic matter to their soil for several years and want the soil tested for o rganic matter content to serve as a report card. Unfortunately, the soil test for organic matter used by the Ag Service Lab is not able to determine the high levels of organic matter found in soils that have been amended with large quantities of compost or animal waste.

The soil test for organic matter is mostly used by farmers who are about to add herbicides to the soil. The soil organic matter ties up herbicides when they are applied to the soil. Subsequently, the more organic matter that there is in the soil, the more herbicide the farmer will have to apply to compensate for the tie-up. The label on the herbicide container will have a table showing how much extra herbicide is required to compensate for a specified range of soil organic matter. As mentioned earl ier, most soils in the southern U.S. are less than 2% organic matter so the herbicide label should be checked to see if an organic matter test is even necessary.