Glossary of Terms in Soil Science

R layer
Underlying consolidated bedrock. See also horizon (soil).
rainfall interception
See precipitation interception.
rawhumus
See mor.
reaction (soil)
The degree of acidity or alkalinity of a soil, usually expressed as a pH value. Descriptive terms commonly associated with certain ranges in pH are: - extremely acid, <4.5 - very strongly acid, 4.5-5.0 - strongly acid, 5.1-5.5 - moderately acid, 5.6-6.0 - slightly acid, 6.1-6.5 - neutral, 6.6-7.3 - slightly alkaline, 7.4-7.8 - moderately alkaline, 7.9-8.4 - strongly alkaline, 8.5-9.0 - very strongly alkaline, >9.0
regolith
The unconsolidated mantle of weathered rock and soil material overlying solid rock.
Regosol
The only great group in the Regosolic order. The soils in the group have insufficient horizon development to meet the requirements of the other orders.
Regosolic
An order of soils having no horizon development or development of the A and B horizons insufficient to meet the requirements of the other orders. See also: Regosolic Soil Classification.
relief
Elevations or inequalities of a land surface, considered collectively. Land having no unevenness or differences of elevation is called level; gentle relief is called undulating, strong relief, rolling, and very strong relief, hilly. See also microrelief.
rendzina
A group of soils having brown to black surface horizons, which have developed on parent material that contains more than 40% calcium carbonate equivalent. Not used in Canadian taxonomy.
residual material
Unconsolidated and partly weathered mineral materials formed by the disintegration of consolidated rock in place.
residual shrinkage
The decrease in volume after the proportionality between water loss and volume change ceases.
residual soil
Soil formed from, or resting on, consolidated rock of the same kind as that from which it was formed and in the same location.
retentivity profile (soil)
A graph showing the retaining capacity of a soil as a function of depth. The retaining capacity may be for water, for water at any given tension, for cations, or for any other substances held by soils.
reversion
Changing of essential plant nutrient elements from soluble to less soluble forms by interaction with or reactions in the soil. Reversion is usually restricted to the conversion of monocalcium phosphate to the less soluble dicalcium phosphate.
reworked
Descriptive of material modified after its preliminary deposition, commonly by water or wind.
rhizobia
Small heterotrophic bacteria of the genus Rhizobium capable of forming symbiotic noduies on the roots of leguminous plants. In the nodules the bacteria fix atmospheric nitrogen that is used by the plants. The bacteria receive their energy from the plants.
rhizoid
In the lower plants, one of the unicellular or multicellular rootlike filaments that serve for attachment and absorption.
rhizoplane
The external surface of roots and of the soil particles and debris adhering to them.
rhizosphere
The soil surrounding and directly influenced by plant roots.
rill
A narrow, very shallow, intermittent water course having steep sides. It presents no obstacle to tilling.
rill erosion
An erosion process in which many small channels a few centimetres deep are formed; it occurs mainly on recently cultivated soils. See also rill.
rill erosion
See erosion (2.).
riverwash
Barren, usually coarse-textured, alluvial soil in and along waterways, exposed at low water levels and subject to shifting during flood periods. A miscellaneous land type.
roche moutonnée
A rounded hummock (boss) of rock smoothed and striated by glacial action and often showing evidence of plucking on the lee side.
rock drumlin
An elongated hill having a veneer of glacial drift over a rock core.
rockland
An area of which usually 25% to 90% is occupied by rock outcrops and most of the remainder by shallow soils. A miscellaneous land type.
rough broken land
An area having steep slopes and many intermittent drainage channels, but usually covered with vegetation. See also miscellaneous land type.
runoff
The portion of the total precipitation on an area that flows away through stream channels. Surface runoff does not enter the soil. Groundwater runoff or seepage flow from groundwater enters the soil before reaching the stream.
Date modified: