Soils - Part 3: Soil Organic Matter Glossary


Soil separates that are grouped into a unit. Aggregates influence bulk density, porosity and pore size.  Principal types of aggregates are platy, prismatic, columnar, blocky and granular.  An aggregate possesses solids and pore space.

carbon-nitrogen ratio

The ratio of the weight of carbon to the weight of nitrogen in a plant material, soil or organism. For example, C/N for sawdust is about 500/1. (Sawdust contains about 500 pounds of carbon for every one pound of nitrogen.)


As a soil separate, clay refers to mineral soil particles which are less than 0.02 millimeters in diameter. As a soil textural class, clay refers to soil material that is 40 percent or more clay, less than 45 percent sand, and less than 40 percent silt.


An organic material in soil which is a product of plant and animal remains that have decomposed and then synthesized into something new.


Element needed in large amounts for plant development; found naturally and in applied fertilizers.

parent material

Rock or minerals which are weathered to form smaller particles of a soil. Parent material is one of the five factors contributing to formation of a specific soil. In the Great Plains, much parent material is associated with ancient seas or glacier deposits.


A key element in the complex nucleic acid structure of plants which regulates protein synthesis; important in cell division and development of new tissues.  Next to nitrogen, the most limiting nutrient in Nebraska crop production; naturally found in sufficient amounts in many Nebraska soils.


An essential plant nutrient needed in large amounts.  Postassium is vital to plant nutrient absorption, respiration, transpiration and enzyme activity. The major portion of potassium is contained in minerals such as feldspar and mica, and clays such as montmorillonite, vermiculite and illite.


Individual rock or mineral fragments in a soil that range from 0.05 to 2.0 millimeters in diameter. Most sand grains consist of quartz, but they can be of any mineral composition.  Sand is also the textural class name of any soil that contains 85 percent or more sand and no more than 10 percent clay.


A soil inorganic separate in the range of 2 to 50 micrometers (or 0.002 to 0.05 mm.). Silt is smaller than sand but larger than clay.

soil structure

The arrangement of soil separates into units called soil aggregates.