Organic Matter

Organic matter is defined as a grouping of carbon containing compounds which have originated from living beings and deposited on or within the earth’s structural components. Soil organic matter includes the remains of all plant and animal bodies which have fallen on the earth’s surface or purposely applied by man in the form of organically synthesized pesticides. A fertile soil should contain from 2 8 percent organic matter, most soils contain less than 2%. In acid, leached soils, which are often sandy, substantial portions of the organic matter is in the form of plant debris and fulvic acids (FAs). In neutral and alkaline soils a large percentage of the organic matter is present in the form of humic acids (HAs) and humin.

When organic matter is burned, there remains a residual ash. The residual ash is composed of the minerals, trace elements required by plants and animals during their normal growth processes. Thus organic matter contains mineral elements required by plants.

An accurate measurement of the organic matter content of the soil would be helpful in monitoring soil fertility. Currently the best extractant for removing organic matter from a soil is 0.5 normal sodium hydroxide (NaOH) (working under N2). The second best extractant is sodium pyrophosphate decahydrate (Na4P2O7 10H2O (pH 9.8)). Neither one of these extractants is able to remove all of the organic matter from a soil sample. Obviously since these chemicals are the best extracts known it is impossible to determine the exact amount of organic matter present within a soil. In realty soil organic matter is not a measurable soil component The organic matter content of a soil sample, reported on soil tests, is only an estimate. The organic carbon content of a soil can be measured and would be a much more valuable indication of the potential humic chemistry of a soil. The soils carbon content would be a desirable part of a soil test report

Recommended Posts