| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

A

A-Horizon

top layer of soil, commonly referred to as topsoil

abiotic

non-living

acid soil

soil material having a pH of less than 7.0

active ingredient

The chemical compound in a product that is responsible for the herbicidal effects.

adsorption

concentration (gas, liquid or dissolved substance) on a surface in condensed layer

adventitious

arising from an unusual place

aeration

process by which air in the soil is replaced by air from the atmosphere

aerobic

having molecular oxygen as a part of the environment

aerobic respiration

respiration occurring in the presence of oxygen

aggregate

group of soil particles cohering in such a way that they behave mecllanically as a unit

agricultural lime

soil amendment consisting principally of calcium carbonate, and including magnesium carbonate and perhaps other materials. It is used to supply calcium and magnesium as essential elements for growth of plants and to neutralize soil acidity

alkali soil

soil having a high degree of alkalinity (pH of 8.5 or higher), or having a nigh exchangeable sodium content, or both A soil thar contains enough alkali (sodiurn) to interfere with the growth of most crop plants

ambient temperature

temperature of the environment in contact with the subject (i.e., temperature of the air surrounding a plant).

ammonification

reduction of ammonium due to biological composition of organic nitrogen compounds

anaerobic

havlng no molecular oxygen in the environment

anaerobic respiration

respiration occurring in the absence of oxygen.

anion

ion carrying a negative charge of electricity

annual

plant which completes its life cycle and dies within one year.

Antheridia

male sex organs of ferns. Found on the prothallus.

archegonia

female sex organs of ferns. Found on the prothallus.

autotrophs

group of bacteria capable of forming nitrite and nitrate

Auxins

growth regulating substances.

available nutrient

portion of any element or compound in the soil that can be readily absorbed and assimilated by growing p'ants

available water

portion of water in a soil that can be readily absorbed by plant roots.

azonal soil

soil without distinct genetic horizons.

B

B-Horizon

second layer in the soil profile, commonly referred to as subsoil.

biotic

living

black frost

frost that occurs when the temperature is below 0°C but above the dew point.

C

C-Horizon

third layer in the soil profile comprised of parent material from which the particular soil has evolved.

callus

layer of thin walled, undifferentiated cells developing on wound surfaces.

carbohydrate

one of the several kinds of sugars produced by plants.

carbon:nitrogen ratio

relative proportion, by weight, of organic carbon to nitrogen in soil or organic matter

carboxylation

process whereby C02 is reduced to an organic compound in photosynthesis (carbon fixation).

cation

ion carrying a positive charge of electricity

cation exchange capacity

total amount of exchangeable cations that a soil can adsorb.

cellulose

carbohydrate formed from the simple sugar glucose. Major component of cell walls in plants.

chernozemic

type of soil developed under grassland.

chlorophyll

green pigment in plants essential for photosynthesis.

Chloroplasts

plastid containing the green pigment called chlorophyll which is used in photosynthesis. Often called the 'seat of food manufacturing' for a plant.

chlorosis

lack of chlorophyll development causing yellowing or whitening of plant tissue.

clay

as a particle-size term: a size fraction less than 0.002 mm in equivalent diameter, or some other limit (geologists and engineers). As a rock term: a natural, earthy, fine grained material that develops plasticity with a small amount of water. As a soil term: a textural class. As a soil separate: a material usually consisting largely of clay minerals but commonly also of amorphous free oxides and primary minerals.

clayey

containing large amounts of clay, or having properties similar to those of clay.

clod

compact, coherent mass of soil produced by digging or plowing. Clods usually slake easily with repeated wetting and drying.

coarse texture

texture exhibited by sands. Ioamy sands, and sandy loams (except very fine sandy loam). A soil containing large quantities of these textural classes.

cold hardiness

condition which must be acquired by perennial plants in order to avoid injury when exposed to freezing temperatures.

colloid

particle small enough to stay suspended in water with a high surface area per unit of mass.

colloid

substance in a state ol fine subdivision, whose particles are 10-6 to 10-7 cm in diameter

compost

organic residues. or a mixture of organic residues and soil, that have been piled, moistened, and allowed to decompose. Mineral fertilizers are sometimes added. If it is produced mainly from plant residue, it is often called artificial manure' or 'synthetic manure' .

contact herbicide

A herbicide that kills only the parts of the plant on which it is applied.

corm

underground swollen base of a stem which stores food.

cosmic radiation

extremely short-wave radiation, from the sun, which is below the wavelengths of the visible spectrum.

cotyledon

thick leaf-like structure in seeds (often called a seed leaf) which functions in the absorption or storage of food .

cross-pollination

transfer of pollen from a stamen to the stigma of a flower of another plant.

cultivar

plant with unique characteristics considered generally superior to those of the plant from which it originated.

cuticle

tough, waxy covering found on the outside surface of insects

D

deadheading

The removal of spent, over-mature flowers.

degradation

changing of a soil to a more highly leached and weathered state, usually accompanied by morphological changes such as the development of an eluviated, light-colored A-horizon

denitrification

by way of anaerobic microbes, the reduction of nitrates to atmospheric nitrogen.

deoxyribonucleic acid (DNA)

carrier of genetic information.

desiccation

type of plant tissue injury resulting from extreme moisture loss. In continental climates, it is generally associated with low temperatures and wind.

dew point

temperature at which the relative humidity reaches 100%.

dieback

starting at the tips, the progressive death of shoots, branches. and roots.

diffusion

movement of molecules from a region of high concentration to a region of lower concentration.

dioecious

plants having either male or female flowers but not both.

E

effective precipitation

net amount available to plants following run-off and evaporation losses.

electrical conductivity

measurement of the ability of a soil water extract to conduct an electrical current expressed in mmhos or mS.

electromagnetic radiation

solar radiation consisting of electromagnetic waves including radio, light, x-ray and gamma rays.

epigeous

pattern of germination

epiphyte

organism found growing non-parasitically on another organism (eg., orchids growing in trees).

erosion

wearing away of the land surface by running water, wind, ice, or other geological agents. including such processes as gravitational creep. Detachment and movement of soil or rock by water, wind, ice, or gravity.

etiolation

morphological expression of a leafy plant that has been grown in the absence of light.

evapo-transpiration

total water transferred from the earth to the atmosphere by evaporation and transpiration .

F

F-l hybrid

first-generation of hybrids which arise from the cross-fertilization of two distinct Species.

fertilizer

any organic or inorganic material of natural or synthetic origin that is added to soil to supply certain elements essential to the growth of plants.

fertilizer grade

expression of the percentage-content of the fertilizer given in the order of N-P-K.

fertilizer ratio

amount of a fertilizer in relation to another or several other fertilizers (i.e., 27-24-7 indicates a ratio of 3:2:1).

field capacity

percentage of water remaining in the soil 2 or 3 days after the soil has been saturated and free drainage has practically ceaaed. The percentage may be expressed in terms of weight or volume.

fixation

process or processes in a soil by which certain chemical elements essential for plant growth are converted from a soluble or exchangeable form to a much less soluble or non-exchangeable form, for example, phosphate fixation.

free energy

energy which is available to do work.

friable

consistence term pertaining to the ease of crumbling of soils.

frond

name usually applied to leaves on ferns.

G

gamete

sex cell either female (egg) or male (sperm)

glyphosate

The active ingredient of a large assortment of non-selective, systemic herbicides that move from the foliage into the roots and kill the entire plant.

H

hemi-cellulose

carbohydrate found in cell walls resembling cellulose containing sugar as well as non-sugar components.

heterozygous

gene pair in which the genes are not identical.

homozygous

gene pair in which both genes are identical.

host

species from which a parasite obtains nourishment

humus

fraction of the soil organic matter that remains after most of the added plant and animal residues have decomposed. It is usually dark colored.

hybridization

the process of creating a new plant by combining the gametes from two separate Species.

hyphae

single tubular filament of a fungi

hypogeous

pattern of germination in which the cotyledons do not emerge from the soil.

I

immobilizatlon

conversion of an element from the inorganic to the organic form in microbial tissues so that the element is not readily available to other organisms or plants.

impervlous

resistant to penetration by fluids or roots.

in situ

in its original place

incipient

initial stage

indigenous

native

infiltratlon

downward entry of water into the soil.

inflorescence

flowers arranged in a cluster.

instar

stage in the life of an insect between two successive molts

internode

section of a plant shoot between adjoining leaves or leaf sets.

ion

electrically charged particle.

ion exchange

replacement of an ion another ion with the same charge.

irrigation

artificial application of water to the soil for the benefit of growing crops .

J

K

L

larva

immature, wingless, wormlike creature hatched from an egg which goes through minor changes to form a pupa

leach

removal of materials in a solution. Usually done by washing out with water.

lignin

organic substance which aids in the hardening of cell walls.

luvisolic

type of soil developed under forests.

M

macronutrient

chemical element necessary in large amounts, usually greater than 1 ppm in the plant, for the growth of plants and usually applied artificially in fertilizer or liming materials. 'Macro' refers to the quantity and not to the essentiality of the element to the plants.

microclimate

climate of a small area as opposed to that of a region of which the small area is a part.

micron

unit of length equivalent to 10-2 metres

micronutrient

chemical element necessary in only small amour.ts, usually less than 1 ppm in the plant, for the growth of plants and the health of animals. 'Micro' refers to the amount, not the essentiality of the element to the orgamsm.

mineralization

change of organic nitrogen through the processes of ammonification and nitrification to forms which the plant can utilize.

molting

shedding and replacement of an outer covering on insects

monoecious

plants having both male and female flowers.

muck soil

organic soil consisting of highly decomposed materials. Mucky peat and peaty muck are terms used to describe increasing stages of decomposition between peat and muck.

mutation

a sudden unexpected heritable change produced by a plant.

mycellium

mass of interwoven hyphae forming the body of fungi

mycorrhiza

non-parasitic fungi which grow in close association with the roots of some plants and aid in the uptake of certain nutrients.

N

neutral soil

soil in which the surface layer, to plow depth, is neither acid nor alkaline in reaction.

nitrification

formation of nitrates from ammonia by soil microbes.

nitrogen fixation

process whereby atmospheric nitrogen is absorbed by soil micro-organisms and converted to forms available to plants.

node

part of the stem where leaves are attached.

non-selective herbicide

A herbicide that kills most if not all plants upon which it is applied.

nymph

juvenile insect resembling an adult which becomes an adult without an intervening pupa stage

O

osmosis

movement of water through a differentially (or selectively) permeable membrane from an area of higher free energy to a region of lower free energy of water molecules.

ovipositor

external egg-laying apparatus of insects

ovule

structure in seed plants containing the female gamete which, upon maturation, develops into the seed.

ozone layer

region in the upper atmosphere where most atmospheric ozone is concentrated.

P

P generation

Parental Species which are used in cross-fertilization to create hybrids.

parasite

lives in or on host from which it obtains nourishment

parent materlal

unconsolidated and more or less chemically weathered mineral or organic matter from which the solum of a soil has developed by pedogenic processes.

parthenocarpy

production of fruit without fertilization.

pathogens

disease-causing organisms.

perennial

plant which lives for more than two years.

perfect flower

stamens and pistil found in the same flower.

petiole

stalk or stem of a leaf.

phloem

food conducting tissue of the vascular system composed of sieve tubes with companion cells, phloem parenchyma and fibres.

photoperiodism

growth or developmental response of a plant to the length of daylight.

photosynthesis

process whereby plants in the presence of light are able to transform carbon dioxide and water to carbon containing energy rich, organic compounds (carbohydrates).

phototropism

process whereby the directional growth of a plant is altered by its reaction to light.

plant pathology

science of plant diseases or disorders.

pore space

space in the soil not occupied by solid particles.

porosity

volume percentage of the total bulk not occupied by solid particles.

predator

species which kills and devours other species

proboscis

extremely slender and shapr, pointed portion of the insects' mouth parts

protein

group of nitrogenous compounds synthesized by plants.

prothallus

small, green, leaf-life structure which develops from the spores of ferns.

pupa

intermediate form from larva to maturity

Q

R

radiation frost

condition which commonly occurs on a clear cold night when the earth and things upon it lose heat by radiative cooling.

reproductive growth

usually follows vegetative growth stage and results in the growth of flowers, fruits and seeds.

respiration

process whereby energy is released though the breakdown of carbon-containing compounds

rest period

physiological condition common to the buds of woody plants beginning at the time of terminal bud formation and ending after exposure to a discrete number of hours of critical low temperature.

rhizome

horizontal underground stem.

ribonucleic acid (RNA)

cellular substance involved in protein synthesis.

rootstock

stems or roots of a plant to which scions are grafted.

runner

stem which grows horizontally over the surface of the soil. Often develops new plants at its tips.

S

saline soil

nonalkali soil that contains enough soluble salts to interfere with the growth of most crop plants.

sand

as a particle term: soil particle between 0.05 and 2.0 mm in diameter. As a soil term: soil textural class.

saprophyte

insect which obtains its food from dead plants or animals

saturate

to fill all the voids between soil particles with a liquid.

scarification

cutting or scratching of the seed coat to facilitate the entry of water and oxygen.

scion

bud or stem of a plant grafted to the rootstock.

sclerotes (ergots)

dense, compacted hyphae remaining dormant during harsh conditions but germinates upon favorable ones .

silt

as a particle term: particle between 0.05 and 0.002 mm in equivalent diameter. As a soil term: textural class.

soil air

soil atmosphere, the gaseous phase of the soil, is the volume not occupied by solid or liquid.

soil organic matter

organic fraction of the soil; includes plant and animal residues at various stages of decomposition, cells and tissue of soil organisms, and substances synthesized by the soil population

soil permeability

ease with which gases and liquids penetrate or pass through a bulk mass of soil or a layer of soil .

soil pH

negative logarithm of the hydrogen-ion activity of a soil. The degree of acidity or alkalinity of a soil as determined by means of a suitable electrode or indicator at a specified moisture content or soil-water ratio, and expressed in terms of the pH scale.

soil profile

vertical section of the soil through all its horizons and extending into the parent material.

soil reaction

degree of acidity or alkalinity of a soil. usually expressed as a pH value.

soil salinity

amount of soluble salts in a soil, expressed in terms of percentage, parts per million, or other convenient ratios.

soil structure

combination or arrangement of primary soil particles into secondary particles, units, or peds. The peds are characterized and classified on the basis of size. shape, and degree of distinctness into classes, types, and grades .

soil texture

proportion of sand, silt, and clay in a soil

solum (plural sola)

upper horizons of a soil in which the parent material has been modified and in which most plant roots are contained. It usually consists of A- and B-horizons.

sori

dense groups of spore cases (sporangia) which contain spores.

spiracles

tiny breathing opening on the body surface of insects.

sprightliness

term used to describe the flavor of a fresh, mature apple containing a combination of acidity, sweetness and aroma.

stigma

distal portion of the pistil of a flower.

stomata

epidermal structure of leaves that function to permit gas exchange between plants and the atmosphere

sucker

shoot arising from underground parts of a plant.

sun-leaves

leaves possessing several layers of palisade cells due to prolonged exposure to intense sunlight.

surfactant

agent which reduces surface tension and allows for a more even dispersal of a substance (e.g., soap breaks the surface tension of water giving a more even spread).

symbiosis

mutually beneficial association of two or more organisms.

systemic herbicide

A herbicide that is able to move within the plant.

T

telescoping

generations new-born insect already carrying the next generation of insects

tilth

physical condition of soil as related to its ease of tillage. Fitness as a seedbed, and impedance to seedling emergence and root penetration.

topsoil

layer of soil rnoved in cultivation. The A-horizon Presumably fertile soil material used to topdress roadbanks, gardens. and lawns

transpiration

release of water vapor from living tissues of the plant.

tropospheric

pertaining to the inner layer of the atmosphere.

tuber

enlarged fleshy underground stem.

U

unavailable water

portion of the soil water that clings so closely to the solid particles in the soil that it cannot be taken up by the plant

V

vector

transporter or viruses from one plant to another

W

water-holding capacity

amount of water a soil can hold, influenced by the size and mix of rnineral particles and the amount of organic matter present.

weathering

physical and chemical disintegration, alteration. and decomposition of rocks and minerals at or near the earth's surface by atmospheric agents.

white frost

frozen dew.

wilting point

moisture content of a soil at which Dlants (specifically sunflower plants) wilt and fail to recover their turgidity when placed in a dark. humid atmosphere .

X

xylem

water conducting tissue of plants.

Y

Z

zonal soil

any one of the great groups of soils having well-developed soil characteristics that reflect the zonal influence of climate and living organisms, mainly vegetation, as active factors of soil genesis.