ABSCISSION. The process by which an old leaf or other is cut off.

ABSORPTION. To take into or suck up. The entrance of a pesticide into an organism through the surface or skin.

ACID SOIL. A soil with a pH below 7.0.

ACTIVE INGREDIENT. The actual pure and toxic agent in a pesticide. The portion of a product responsible for its activity. Abbreviated as a.i. Example: 4 lbs. A.i. per gallon.

ACUMINATE. Describes a grass leaf blade that gradually tapers to a long point.

ACUTE. Describes a sharply pointed grass leaf blade.

ADHERENCE. The tendency or property of a pesticide or other substance to stick to a surface.

ADJUVANT. A substance which serves to aid or contribute to the performance of a spray material.

ADNATE. Adhering to, or joined to as the margins of a leaf blade join to form a tube.

ADSORPTION.The binding of a pesticide or other substance to the outside surface of a soil particle or plant part. Opposite of absorption.

ADVENTITIOUS(root). A root arising other than as a branch root.

AERIFICATION(aeration). Term that refers to hole punching in the soil, even if not for improved air circulation. May refer to slicing also.

AEROBE. Any organism that requires a regular supply of atmospheric oxygen to survive.

AGGREGATE. (1) Soil particles cemented together to form a granule. (2) The process of forming into such particles.

ALGAE. Microscopic, non-vascular plants, usually found growing in areas of poor drainage, low light, and poor fertility.

ALKALI. A soil with a high percentage of Na+ ions.

ALLELOPATHY. A repressive influence of one plant upon another because of secretions or chemical influence other than crowding or competition.

ALTERNATE HOST. One of two kinds of plants on which a parasitic fungus must develop to complete its life cycle. Rush (Puccinia spp.) is an example of a turfgrass disease having an alternate host, usually Buckthorn or Barberry.

AMMONIACAL. An immediate release source of nitrogen found in some fertilisers.

ANAEROBIC. Essentially without oxygen. Refers to organisms that can exist without oxygen.