Determination of Organic Matter in Soil

Purpose:

This test is performed to determine the organic content of soils. The organic content is the ratio, expressed as a percentage, of the mass of organic matter in a given mass of soil to the mass of the dry soil solids.

Standard Reference:

ASTM D 2974 – Standard Test Methods for Moisture, Ash, and Organic Matter of Peat and Organic Soils

Significance:

Organic matter influences many of the physical, chemical and biological properties of soils. Some of the properties influenced by organic matter include soil structure, soil compressibility and shear strength. In addition, it also affects the water holding capacity, nutrient contributions, biological activity, and water and air infiltration rates.

Equipment:

• Muffle furnace,
• Balance,
• Porcelain dish,
• Spatula,
• Tongs

Test Procedure:

(1) Determine and record the mass of an empty, clean, and dry porcelain dish (M_P).

(2) Place a part of or the entire oven-dried test specimen from the moisture content experiment in the porcelain dish and determine and record the mass of the dish and soil specimen (M_PDS).

(3) Place the dish in a muffle furnace. Gradually increase the temperature in the furnace to 440⁰C. Leave the specimen in the furnace overnight.

(4) Remove carefully the porcelain dish using the tongs (the dish is very hot), and allow it to cool to room temperature. Determine and record the mass of the dish containing the ash (burned soil) (M_PA).

(5) Empty the dish and clean it.

Data Analysis:

(1) Determine the mass of the dry soil.

M_D=M_PDS-M_P

(2) Determine the mass of the ashed (burned) soil.

M_A=M_PA-M_P

(3) Determine the mass of organic matter

M_O = M_D – M_A

(4) Determine the organic matter (content).

OM = (M_O/M_D)*100

Article written by

Prof. Krishna Reddy, UIC