Ch. 10 Key Terms

mycorrhizal symbiosis

An association between the roots of most plant species and certain fungi. The plant provides organic compounds to the fungus, while the fungus provides water and nutrients to the plant.

topsoil

The uppermost layer of a soil, including the “O” and “A” layers, which are usually rich in organic material.

subsoil

A layer of soil beneath the topsoil that has lower organic content and higher concentrations of fine mineral particles; often contains soluble compounds and clay particles carried down by percolating water.

sheet erosion

The peeling off of thin layers of soil from the land surface; accomplished primarily by wind and water.

rill erosion

The removal of thin layers of soil by little rivulets of running water that gather and cut small channels in the soil.

gully erosion

Removal of layers of soil, creating channels or ravines too large to be removed by normal tillage operations.

desertification

Conversion of productive lands to desert.

waterlogging

Water saturation of soil that fills all air spaces and causes plant roots to die from lack of oxygen; a result of overirrigation.

salinization

A process in which mineral salts accumulate in the soil, killing plants; occurs when soils in dry climates are irrigated profusely.

contour plowing

Plowing along hill contours; reduces erosion.

terracing

Shaping the land to create level shelves of earth to hold water and soil; requires extensive hand labor or expensive machinery, but enables farmers to farm very steep hillsides.

cover crops

Plants, such as rye, alfalfa, or clover, that can be planted immediately after harvest to hold and protect the soil.

negative emissions technologies

Techniques to reduce greenhouse gas emissions or to remove greenhouse gases from the atmosphere.

pesticide

Any chemical that kills, controls, drives away, or modifies the behavior of a pest.

biocide

A broad-spectrum poison that kills a wide range of organisms.

herbicide

A chemical that kills plants.

insecticide

A chemical that kills insects.

fungicide

A chemical that kills fungi.

organophosphates

Organic molecules to which one or more phosphate groups are attached.

chlorinated hydrocarbons

Hydrocarbon molecules to which chlorine atoms are attached.

neonicotinoid

Pesticides with a chemical structure similar to nicotine. Thought to be a cause of massive bee deaths.

fumigants

Toxic gases such as methyl bromine that are used to kill pests.

inorganic pesticides

Inorganic chemicals such as metals, acids, or bases used as pesticides.

natural organic pesticides

“Botanicals” or organic compounds naturally occurring in plants, animals, or microbes that serve as pesticides.

microbial agents

Beneficial microbes (bacteria, fungi) that can be used to suppress or control pests; also called biological controls.

biological controls

Use of natural predators, pathogens, or competitors to regulate pest populations.

pest resurgence

Rebound of pest populations due to acquired resistance to chemicals and nonspecific destruction of natural predators and competitors by broadscale pesticides.

pesticide treadmill

A need for constantly increasing doses or new pesticides to prevent pest resurgence.

persistent organic pollutants (POPs)

Chemical compounds that persist in the environment and retain biological activity for a long time.

integrated pest management (IPM)

An ecologically based pest-control strategy that relies on natural mortality factors, such as natural enemies, weather, cultural control methods, and carefully applied doses of pesticides.