Key Terms in Plant Biology and Agronomy

abaxial

Located away from the axis side; for example, the underside of a leaf.

AB-DTPA extractant

Acronym for an extraction reagent of ammonium bicarbonate (AB) in diethylenetriamine-penta acetic acid (DTPA) with a pH of 7.6 used to extract P, K, Na, Fe, Mn, and Zn from alkaline soils.

abiotic

Nonliving environmental elements such as rainfall, temperature, wind, lightning, and minerals.

abscisic acid

Plant hormone that, among other things, promotes bud dormancy, maintains seed dormancy, and causes stomatal closing.

absorption

In plants, passing of a compound from one system into another, such as water movement from soil into roots; in soils, binding of a chemical into a soil particle.

acclimation

Physical and physiological processes in plants that prepare them for temperature extremes, such as winter.

acervulus

Erumpent, cushion-like mass of black spore-bearing hyphae, with prominent black spines (or setae), often correlated with Colletotrichum graminicola, the causal pathogen of anthracnose.

acid equivalent (ae)

Theoretical amount of parent acid from the active ingredient content found in a pesticide formulation.

acid injection

Adding acidic materials such as sulfur or phosphoric acid to irrigation water with excessive pH, bicarbonate, and carbonate contents. This lowers the pH and converts bicarbonate and carbonate into carbon dioxide and water.

acid rain

Rainwater with a pH below 5.6.

acidity

pH of a soil or solution with a value

acropetal

Toward the top of a plant.

actinomycetes

Microorganisms that are intermediate between bacteria and fungi.

activated sludge

Aerated sludge subjected to bacterial processes and used as a fertilizer or soil amendment.

active acidity

Acidity of a soil solution from free hydrogen ions measured as pH; also called potential acidity and buffer capacity.

active ingredient (ai)

Actual amount of active concentration in a formulation; for example, Aatrex 4L contains 4 pounds of active ingredient per gallon of product, and Ronstar 2G has 2% active ingredient per pound of product.

Adam-Evans buffer

Buffer solution used for measuring H+ ions and to determine lime requirements for acid.

adaptation

Unique structure, physiology, or process that aids an organism to fit into its environment.

adaxial

Located toward the axis side, for example, the upper side of a leaf.

adenosine triphosphate (ATP)

Nucleotide consisting of adenine, ribose sugar, and three phosphate groups that, upon metabolism, provide usable chemical energy. On hydrolysis, energy is released when ATP loses one phosphate group to become adenosine diphosphate (ADP).

adhesion

Molecular attraction and contact between the surfaces of two unlike substances or objects.

adjuvant

Substance in a formulation that enhances its effectiveness. Includes surfactants, crop oils, crop oil concentrates, antifoaming agents, drift control agents, pH modifiers, and compatibility agents.

adsorption

Bonding or adhering of ions or compounds to the surface of soil particles or plant parts.

adventitious bud

Bud produced in an unusual or unexpected place; for example, near a point of stem injury or on a leaf or a root.

activity index

Cold water insoluble nitrogen (CWIN) percentage of a fertilizer that is soluble in hot (100°C) water, of not less than 40%.

acute toxicity

Ability of a substance to cause injury or death shortly following exposure, usually due to a relatively large dose.

adventitious root

Root originating in an unusual or unexpected place, such as from stem or leaf tissue instead of from another root.

aerification

In turf, a method of cultivation where hollow or solid tines or spoons are inserted into and removed from the turf to control soil compaction and increase water and fertilizer penetration.

aerobic

Requiring oxygen or having oxygen present in the environment.

aggregate

To collect together in tufts, groups, or bunches, such as soil clods.

agronomy

Science of crops and soils.

aleurone layer

Layer of high-protein cells in seeds surrounding the storage cells of endosperm. It secretes enzymes for digesting food reserves in the endosperm during seed germination.

alga (plural: algae)

Single- to multiple-celled plant found in damp habitats containing chlorophyll and having no true roots, stems, or leaves.

algal bloom

Population explosion of algae that is often followed by green- or red-colored water and low oxygen.