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Glossary
Alkaline soil. A soil with a pH above 7, containing
more base than acid.
Allelopathic effect. The effect that some plants
have in suppressing the germination or growth of other plants. The
chemicals responsible for this effect are produced during the growth
of a plant or during the decomposition of its residues.
Acid. A solution containing free hydrogen ions
(H + ) or a chemical that will give off hydrogen ions
into solution.
Acidic soil. A soil that as a pH below 7. The
lower the pH, the more acidic is the soil.
Aggregates. The structures, or clumps, formed
when soil minerals and organic matter are bound together with the
help of organic molecules, plant roots, fungi, and clays.
Anion. A negatively charged element or molecule
such as chloride (Cl - ) or nitrate (NO3-).
Ammonium (NH4 + ). A
form of nitrogen that is available to plants and is produced in
the early stage of organic matter decomposition.
Available nutrient. The form of a nutrient
that a plant is able to use. Nutrients that the plant needs are
commonly found in the soil in forms that the plant can’t use
(such as organic forms of nitrogen) and must be converted into forms
that the plant is able to take into the roots and use (such as the
nitrate form of nitrogen).
Ball test. A simple field test to determine
soil readiness for tillage. A handful of soil is taken and squeezed
into a ball. If the soil molds together, it is in the plastic state
and too wet for tillage or field traffic. If it crumbles, it is
in the friable state.
Base. Something that will neutralize an acid,
such as hydroxide or limestone.
Beds. Small hilled-up, or raised, zones where
crops (usually vegetables) are planted. They provide better-drained
and warmer soil conditions. Similar to ridges, but are generally
broader, and are usually shaped after conventional tillage has occurred.
Buffering. The slowdown or inhibition of changes.
A substance that has the ability to buffer a solution is also called
a buffer. Buffering can slow down pH changes by neutralizing acids
or bases.
Bulk density. The mass of dry soil per unit
volume. It is an indicator of the compactness of the soil.
Calcareous soil. A soil in which finely divided
lime is naturally distributed, usually has a pH from 7 to slightly
more than 8.
Cation. A positively charged ion such as calcium
(Ca ++ ) or ammonium (NH4+ ).
Cation exchange capacity (CEC). The amount
of negative charge that exists on humus and clays, allowing them
to hold onto positively charged chemicals (cations).
Chelate. A molecule that uses more than one
bond to attach strongly to certain elements such as iron (Fe++
) and zinc (Zn++ ). These elements may later be released
from the chelate and used by plants.
Coarse textured. Soil dominated by large mineral
particles (sand size). May also include gravels. Previously called
“light soil.”
Colloid. A very small particle, with a high
surface area, that can stay in a water suspension for a very long
time. The colloids in soils, the clay and humus molecules, are usually
found in larger aggregates and not as individual particles. These
colloids are responsible for many of the chemical and physical properties
of soils, including cation exchange capacity, chelation of micronutrients,
and the development of aggregates.
Compost. Organic material that has been well
decomposed by organisms under conditions of good aeration and high
temperature, often used as a soil amendment.
Controlled traffic. Field equipment is restricted
to limited travel or access lanes in order to reduce compaction
on the rest of the field.
Conventional tillage. Preparation of soil for
planting by using the moldboard plow followed by disking or harrowing.
It usually breaks down aggregates, buries most crop residues and
manures, and leaves the soil smooth.
Coulter. A fluted or rippled disk mounted on
the front of a planter to cut surface crop residues and perform
minimal soil loosening prior to seed placement. Multiple coulters
are used on zone-till planters to provide a wider band of loosened
soil.
Cover crop. A crop grown for the purpose of
protecting the soil from erosion during the time of the year when
the soil would otherwise be bare. It is sometimes called a green
manure crop.
Crumb. A soft, porous, more-or-less round soil
aggregate. Generally indicative of good soil tilth.
Crust. A thin, dense layer at the soil surface
that becomes hard upon drying.
C:N ratio. The amount of carbon in a residue
divided by the amount of nitrogen. A high ratio results in low rates
of decomposition and can also result in a temporary decrease in
nitrogen nutrition for plants, as micro-organisms use much of the
available nitrogen.
Deep tillage. Tillage practices that loosen
the soil at greater depths (usually greater than 12 inches) than
during regular tillage.
Disk. An implement for harrowing, or breaking
up, the soil. It is commonly used following a moldboard plow, but
is also used by itself to break down aggregates, help mix fertilizers
and manures with the soil, and smooth the soil surface.
Drainage. The process of soil water loss by
percolation through the profile as a result of the gravitational
force. Also: Removal of excess soil water through the use of channels,
ditches, soil shaping and subsurface drain pipes.
Element. All matter is made up of elements,
seventeen of which are essential for plant growth. Elements such
as carbon, oxygen, and nitrogen combine to form larger molecules.
Erosion. Wearing away of the land surface by
runoff water (water erosion), wind shear (wind erosion) or tillage
(tillage erosion).
Field capacity. Water content of a soil following
drainage by gravity.
Fine textured. Soils dominated by small mineral
particles (silt and clay). Previously called “heavy soil.”
Friable. Consistency status when soil crumbles
instead of being molded when a force is applied.
Frost tillage. Tillage practices performed
when a shallow (2–4 inches) frozen layer exists at the soil
surface.
Full-field (full-width) tillage. Any tillage
system that results in soil loosening over the entire width of the
tillage pass. For example, mold-board plowing, chisel tillage, and
disking.
Green manure. A crop grown for the main purpose
of building up or maintaining soil organic matter. It is sometimes
called a cover crop.
Heavy soil. Nowadays usually called “fine
texture” soil, it contains a lot of clay and is usually more
difficult to work than coarser texture soil. It normally drains
slowly following rain.
Humus. The very well decomposed part of the
soil organic matter. It has a high cation exchange capacity.
Infiltration. The process of water entering
into the soil at the surface.
Inorganic. Chemicals that are not made from
chains or rings of carbon atoms (for example, soil clay minerals,
nitrate, and calcium).
Least-limiting water range. See optimum water
range.
Legume. A group of plants including beans,
peas, clovers, and alfalfa that forms a symbiotic relationship with
nitrogen-fixing bacteria living in their roots. These bacteria help
to supply plants with an available source of nitrogen.
Lignin. A substance found in woody tissue and
in stems of plants that is difficult for soil organisms to decompose.
Lime, or limestone. A mineral that can neutralize
acids and is commonly applied to acid soils, consisting of calcium
carbonate (CaCO3 ).
Loess soils. Soils formed from windblown deposits
of silty and fine-sand-size minerals. They are easily eroded by
wind and water.
Micronutrient. An element, such as zinc, iron,
copper, boron, and manganese, needed by plants only in small amounts.
Microorganism. Very small and simple organism
such as bacteria and fungi.
Mineralization. The process by which soil organisms
change organic elements into the “mineral” or inorganic
form as they decompose organic matter (for example, organic forms
of nitrogen are converted to nitrate).
Moldboard plow. A commonly used plow that completely
turns over the soil and incorporates any surface residues, manures,
or fertilizers deeper into the soil.
Monoculture. Production of the same crop in
the same field year after year.
Mycorrhizal relationship. The mutually beneficial
relationship that develops between plant roots of most crops and
fungi. The fungi help plants obtain water and phosphorus by acting
like an extension of the root system and in return receive energy-containing
chemical nutrients from the plant.
Nitrate (NO3 -). The
form of nitrogen that is most readily available to plants. It is
the nitrogen form normally found in the greatest abundance in agricultural
soils.
Nitrogen fixation. The conversion of atmospheric
nitrogen by bacteria to a form that plants can use. A small number
of bacteria, which include the rhizobia living in the roots of legumes,
are able to make this conversion.
Nitrogen immobilization. The transformation
of available forms of nitrogen, such as nitrate and ammonium, into
organic forms that are not readily available to plants.
No-till. A system of planting crops without
tilling the soil with a plow, disk, chisel, or other tillage implement.
Optimum tillage water range. The range of soil
water contents in which plants do not experience stress from drought,
high soil strength, or lack of aeration.
Organic. Chemicals that contain chains or rings
of carbon connected to one another. Most of the chemicals in plants,
animals, microorganisms, and soil organic matter are organic.
Oxidation. The combining of a chemical such
as carbon with oxygen, usually resulting in the release of energy.
Penetrometer. A device measuring soil resistance
to penetration, an indicator of the degree of compaction. Includes
a cone-tipped metal shaft that is slowly pushed into the soil while
the resistance force is measured.
Perennial forage crops. Crops such as grasses,
legumes, or grass/legume mixtures that form complete soil cover
(sods) and are grown for pasture or to make hay and haylage for
animal feed.
pH. A way of expressing the acid status, or
hydrogen ion (H+ ) concentration, of a soil or a solution
on a scale where 7 is neutral, less than 7 is acidic, and greater
than 7 is basic.
Photosynthesis. The process by which green
plants capture the energy of sunlight and use carbon dioxide from
the atmosphere to make molecules needed for growth and development.
Plastic. State of a soil when it molds easily
when a force is applied. Compare to friable.
Plastic limit. Water content of soil at the
transition from the plastic to the friable state. Upper limit of
soil moisture where tillage and field traffic do not result in excessive
compaction damage.
Polyculture. Growth of more than one crop in
a field at the same time.
PSNT. The Pre-Sidedress Nitrate Test is a soil
test for nitrogen availability where the soil is sampled to 1 ft
depth during the early crop growth.
Respiration. The biological process that allows
living things to use the energy stored in organic chemicals. In
this process, carbon dioxide is released as energy is made available
to do all sorts of work.
Restricted tillage. Any tillage system that
includes only limited and localized soil disturbance in bands where
plant rows are to be established. For example, no-till, zone-till,
strip-till and ridge-till. Compare with full-field tillage.
Rhizobia bacteria. Bacteria that live in the
roots of legumes and have a mutually beneficial relationship with
the plant. These bacteria fix nitrogen, providing it to the plant
in an available form, and in return receive energy-rich molecules
that the plant produces.
Ridge tillage. Crops are planted on top of
a small ridge (usually 2–4 inches height) which is generally
reformed annually with a special cultivator.
Rotation effect. The crop-yield benefit from
rotations that includes better nutrient availability, fewer pest
problems, and better soil structure.
Runoff. Water lost by flow over the soil surface.
Saline soil. A soil that contains excess free
salts, usually sodium and calcium chlorides.
Saturation, soil. When all soil pores are water-filled
(a virtual absence of soil air).
Silage. A feed produced when chopped-up corn
plants or wilted hay are put into airtight storage facilities (silos)
and partially fermented by bacteria. The acidity produced by the
fermentation and the lack of oxygen help preserve the quality of
the feed during storage.
Slurry (manure). A manure that is between solid
and liquid. It flows slowly and has the consistency of something
like a very thick soup.
Sod crops. Grasses or legumes such as timothy
and white clover that tend to grow very close together and form
a dense cover over the entire soil surface.
Sodic soil. A soil containing excess amounts
of sodium. If it is not also saline, clay particles disperse and
the soil structure may be poor.
Strip cropping. Growing two or more crops in
alternating strips, usually along the contour or perpendicular to
the prevailing wind direction.
Structure. The physical condition of the soil.
It depends upon the amount of pores, the arrangement of soil solids
into aggregates, and the degree of compaction.
Texture. A name that indicates the relative
significance of a soil’s sand, silt, and clay content. The
term “coarse texture” means that a soil has a high sand
content, while “fine texture” means that a soil has a
high clay content.
Thermophilic bacteria. Bacteria that live and
work best under high temperatures, around 110 to 140 F. They are
responsible for the most intense stage of decomposition that occurs
during composting.
Tillage. The mechanical manipulation of soil,
generally for the purpose of creating soil loosening, a seedbed,
controlling weeds, and incorporation of amendments. Primary tillage
(moldboard plowing, chiseling) is a more rigorous practice, primarily
for soil loosening and incorporation of amendments. Secondary tillage
(disking, harrowing) is a less rigorous practice following primary
tillage that creates a seedbed containing fine aggregates.
Tillage erosion. The downslope movement of
soil through the action of tillage implements.
Tilth. The physical condition, or structure,
of the soil as it influences plant growth. A soil with good tilth
is very porous and allows rainfall to infiltrate easily, permits
roots to grow without obstruction, and is easy to work.
Wilting point. The moisture content when a
soil contains only water that is too tightly held to be available
to plants.
Zone tillage. A restricted tillage system that
establishes a narrow (4–6 inches width) band of loosened soil
with surface residues removed. This is accomplished using multiple
coulters and row cleaners as attachments on a planter. May also
include a separate “zone-building” practice that provides
deep, narrow ripping without significant surface disturbance. A
modification of no tillage, generally better adapted to cold and
wet soils.
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