ISA Arborist Chapter 3: Soil Science

Actinomycete

Group of soil bacteria resembling fungi. Actinomycetes play a role in the decomposition of organic matter and the release of mineral elements.

Aggregate

Close cluster or mix of small particles of soil and or organic matter of varying sizes that bond together ;sand ,gravel,small rocks.

Anion

Ion that carries a negative charge. Contrast with cation.

Buffering capacity

Ability of a soil to maintain(I.e.,to resist change)in its pH.

Bulk density

Mass of soil per unit volume. Often used as a measure of compaction.

Capillary water

Water held in the capillary pores of the soil;much of this water can move in any direction and is readily available to plant roots.

Cation

Positively charged ion. In soils, the most abundant cations are calcium (Ca), magnesium (Ma),potassium (K),sodium(Na),and aluminum(AI). Contrast with anion.

Cation exchange capacity(CEC)

Ability of a soil to absorb and hold cations. Affected by soil pH. Measures soil fertility,clay composition,and engineering characteristics.

Clay

Soil particles with a typical grain size less 0.004mm. Soil predominantly composed of such particles. Contrast with sand and silt.

Exudates

Substance or solution that oozes out of a injured plant cells or is secreted through membrane pores.

Field capacity

Maximum soil moister content following the drainage of water due to the force of gravity . Compare to available water ,gravitational water and permanent wilting point.

Gravitational water

Water that drains from the larger soil Macropores due to the force of gravity.

Horizon

Layer of soil within the soil profile

Humus

Dark colored,stable form of organic matter that remains after most of the plant and animal residues have decomposed.

Ion

Atom or a group of atoms with a positive or negative charge.

Leach

Tendency for elements or compounds to wash into the soil.

Loam

Soil texture classification based on a certain ratio of sand,silt and clay. Considered ideal for plant growth.

Macropore

Relatively large space between soil particles that is usually air filled and allows for water movement and root penetration.

Micropore

Space between soil particles that is relatively small and likely to be water filled.

Mineralization

Process in which an organic substance is converted to or trapped in inorganic substance.

Mycorrhizae

Symbiotic association between certain fungi and the roots of plants.

Nematode

Microscopic roundworm. Many are beneficial organisms,but some feed on plant tissues and may cause disease or damage.

Nutrient cycling

Movement of mineral elements (nutrients) within an ecosystem as organic matter decomposes,releasing bound nutrients back to plants.

Organic layering

Layer of organic matter at the soil surface.

Parent material

Soil bedrock or base material from which a soil profile develops.

Permanent wilting point

Point at which a plant cannot pull any more water from the soil and suffers permanent damage.

PH

Unit of measure that describes the alkalinity or acidity of a solution. Negative log of the hydrogen ion concentration . Measured on a scale from 0 to 14. Greater than 7 is alkaline, less than 7 is acid,and 7 is neutral (pure water).

Rhizosphere

Soil area immediately adjacent to,and affected by,plant roots. Typically has a high level of microbial activity.

Saline soil

Soil with a high consent ration of soluble salts. Can cause poor plant growth.

Sand

Soil particles with a size between 0.06 and 2.0 mm in diameter.

Silt

Soil particles with a grain size between 0.004 and0.062mm . Coarser than clay particles but finer than sand.

Sodic soil

Soil with relatively low levels of soluble salts and a concentration of sodium high enough to adversely affect soil structure (symptoms include water logging,erosion ,soil surface crusting,and poor plant growth). Soils>12SAR(sodium absorption rate).

Soil compaction

Compression of the soil,often the result of vehicle or heavy equipment traffic,that breaks down soil aggregates and reduces soil volume and total pore space,especially microspore space.

Soil food web

Complex network of interconnected food chains in an ecosystem;in this case,in the soil.

Soil profile

Vertical section through the soil and all of the soil horizons.

Soil structure

Arrangement of soil particles into aggregates

Soil texture

Relative fineness or coarseness of a soil due to particle size (sand,silt,and clay).

Structural cells

Modular system consisting of units of soil and integrated support structures that serve as both a foundation for paved surfaces and a hospitable environment for tree root growth.

Structural soil

Pavement substrate that can be compacted to meet engineering specification yet remains penetrable by tree roots in the urban environment. Composed of angular crushed stone,clay loam,and hydrogel mixed in a weight ratio of 100:20:0.03. Developed at the Urban Horticulture institute,Cornell university,Ithaca ,NY.

Suspended sidewalk

Sidewalk that is reinforced and supported with piers or other structures so that it does not rely on compacted sub grade or soil for support.

Symbiotic

Association of two different types of living organisms that is often,but not always,beneficial to each.

Water-holding capacity

Ability of a soil to hold moisture.