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How to Calculate the Organic Content of Soil
How to Calculate the Organic Content of Soil. Maintaining a healthy percentage of organic materials in the soil is a critical component of any garden. The University of Minnesota Extension states soil utilizes organic materials for a variety of uses, including providing plants with nutrients, aiding in irrigation, lowering evaporation rates,...
Maintaining a healthy percentage of organic materials in the soil is a critical component of any garden. The University of Minnesota Extension states soil utilizes organic materials for a variety of uses, including providing plants with nutrients, aiding in irrigation, lowering evaporation rates, increasing the nutrient-holding capacity of the soil and providing food for worms, bacteria and other soil organisms. Most soil tests found at garden supply stores or conducted by cooperative extensions inform gardeners of the organic content percentage in their soil, but the organic content of soil can also be calculated at home.
Things You'll Need
Hand spade
Oven-proof container
Oven
Scale with resolution of 0.1 grams
Covered evaporating dish or crucible
Metal stand
Propane torch
Dig a soil sample from the lawn or garden. Four or five samples taken at a depth of 6 inches should provide accurate soil readings. Thoroughly mix the samples and deposit the soil in an oven-safe container.
Dry the sample in the oven. The New Mexico State University Weather Center recommends baking the soil at 105 degrees Fahrenheit until dry.
Weigh the evaporating dish or crucible and its lid. Record the measurement. Weigh out 10 grams of dried soil and add to the crucible. Cover the crucible and weigh the crucible, soil and lid together.
Place the container on a metal stand. Tilt the lid at a slight angle to allow gasses to escape. The metal stand should be placed on a non-flammable surface.
Heat the crucible with a propane torch. Extreme caution should be used when operating a propane torch. Avoid touching both the crucible and the metal stand, which will quickly become hot. Continue heating the crucible until fumes completely stop exiting the space between the crucible lip and the lid. The fumes are the organic content in the soil burning off.
Allow the crucible, soil and stand to cool completely. Do not attempt to handle while still hot.
Weigh the covered soil sample. Subtract the weight of the crucible and lid from the total, leaving you with the weight of the heated soil sample. Subtract the weight of the heated sample from the original soil sample weight of 10 grams. Each 0.1 gram of weight removed from the sample represents 1 percent of organic content in the soil. If the original sample weighed 10 grams, and the heated sample weighed 9.3 grams, 0.7 grams -- or 7 percent -- of organic content was burned off. This means the soil contains 7 percent organic materials.
Tips & Warnings
The Michigan State University Extension says organic materials should compose 7 to 10 percent of soil.
