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Northern Research Station
One Gifford Pinchot Drive
Madison, WI 53726
(608) 231-9318
(608) 231-9544 TTY/TDD

Soil Quality



Acidity, active The activity of hydrogen ion in the aqueous phase of a soil expressed as a pH value.

Acidity, residual Soil acidity that is neutralized by lime or a buffered salt solution to raise the pH to a specified value (usually 7.0 or 8.0) but which cannot be replaced by an unbuffered salt solution. It can be calculated by subtraction of salt replaceable acidity from total acidity.

Acidity (exchangeable) The aluminum and hydrogen that can be replaced from an acid soil by an unbuffered salt solution such as KCl or NaCl

Adsorption The attraction of ions or compounds to the surface of a solid

Air-filled porosity The fraction of the bulk volume of soil that is filled with air at any given time or under a given condition, such as a specified soil-water content or soil-water metric potential.

Anion A negatively charged ion (e.g., PO4-, NO3-)

Bulk density The mass of dry soil per unit bulk volume. The value is expressed as grams per cubic centimeter (g cm-3)

Carbon cycle The sequence of transformations whereby carbon dioxide is converted to organic forms by photosynthesis or chemosynthesis, recycled through the biosphere (with partial incorporation into sediments), and ultimately returned to its original state through respiration or combustion.

C:N ratio The ratio of the mass of organic carbon to the mass of organic nitrogen in soil, organic material, plants, or microbial cells.

Cation A positively charged ion (e.g., Na+, Ca++)

Cation Exchange
Capacity (CEC) The sum of exchangeable bases plus total soil acidity at a specific pH values,usually 7.0 or 8.0. Expressed in centimoles of charge per kilogram of exchanger (cmolc kg-1).

Clay (i) A soil separate consisting of particles <0.002 mm in equivalent diameter. (ii) A textural class. (iii) A naturally occurring material composed primarily of fine-grained minerals, which is generally plastic at appropriate water contents and will harden when dried or fired.

Effective Cation
Exchange Capacity
(ECEC) When acidity is expressed as salt extractable acidity, the cation exchange capacity is called the effective cation exchange capacity (ECEC) because this is considered to be the CEC of the exchanger at the native pH value. Expressed in centimoles of charge per kilogram of exchanger (cmolc kg-1).

Erosion The wearing away of the land surface by rain or irrigation water, wind, ice, or other natural or anthropogenic agents that abrade, detach and remove geologic parent material or soil from one point on the earth's surface and deposit it elsewhere

Nutrient A plant nutrient that is held by the adsorption complex of the soil and is easily exchanged with the anion or cation of neutral salt solutions.

Litter The surface layer of the forest floor which is not in an advanced stage of decomposition, usually consisting of freshly fallen leaves, needles, twigs, stems, bark, and fruits.

Mineral Soil A soil consisting predominantly of products derived from the weathering of rocks (e.g., sands, silts, and clays).

Nutrient Elements or compounds essential as raw materials for organism growth and development.

O horizon A layer of organic material having undergone little or no decomposition (fibric material). On the forest floor this layer consists of freshly fallen leaves, needles, twigs, stems, bark, and fruits.

Organic soil For the purposes of FIA, an organic soil is defined as any soil in which the organic horizon is greater than 8 inches (20 cm) in thickness. These soils are prevalent in wetland areas such as bogs and marshes and may be frequently encountered in certain regions of the country (e.g., Maine, northern Minnesota, coastal regions)

pH The pH of a solution in equilibrium with soil. It is determined by means of an electrode or other indicator at a specified soil-solution ratio in a specified solution, usually distilled water, 0.01 M CaCl2, or 1 M KCl.

Plant nutrient An element which is absorbed by plants and is necessary for completion of the normal life cycle. These include C, H, O, N, P, K, Ca, Mg, S, Cu, Fe, Zn, Mn, B, Cl, Ni, and Mo.

Porosity The volume of pores in a soil sample (nonsolid volume) divided by the bulk volume of the sample

Restrictive layer In FIA, defined as any soil condition that increases soil density to the extent that it may limit root growth. This limitation may be physical (hard rock) or chemical (acid layer) or both.

Sampling frame In FIA, a frame used to collect forest floor samples from a known area. A bicycle tire 12 inches in diameter has been selected as the national standard.

Soil profile A vertical section of the soil through all its horizons and extending into the C horizon.

Water content The water lost from the soil upon drying to constant mass at 105 ° C; expressed either as the mass of water per unit mass of dry soil or as the volume of water per unit bulk volume of soil.



Last Modified: 02/06/2007