Chapter 37: Soil and Plant Nutrition

Vocabulary from Campbell's Biology

Humus

Decomposing organic material that is a component of topsoil.

Topsoil

A mixture of particles derived from rock, living organisms, and decaying organic material (humus).

Soil Horizons

A soil layer with physical characteristics that differ from those of the layers above or beneath.

Loams

The most fertile soil type, made up of roughly equal amounts of sand, silt, and clay.

Cation Exchange

A process in which positively charged minerals are made available to a plant when hydrogen ions in the soil displace mineral ions from the clay particles.

Fertilization

The addition of mineral nutrients to the soil.

Sustainable Agriculture

Long-term productive farming methods that are environmentally safe.

No-Till Agriculture

A plowing technique that minimally disturbs the soil, thereby reducing soil loss.

Phytoremediation

An emerging technology that reclaims contaminated areas by using plant species able to extract heavy metals and pollutants from soil and concentrate them in easily harvested tissues.

Essential Element

A chemical element required for an organism to survive, grow, and reproduce.

Hydroponic Culture

A method in which plants are grown in mineral solutions rather than in soil.

Macronutrients

An essential element that an organism must obtain in relatively large amounts.

Micronutrients

An essential element that an organism needs in very small amounts.

Rhizobacteria

A soil bacterium whose population size is much enhanced in the rhizosphere, the soil region close to a plant’s roots.

Rhizosphere

The soil region close to plant roots and characterized by high microbiological activity.

Endophytes

A harmless fungus, or occasionally another organism, that lives between cells of a plant part or multicellular alga.

Nitrogen Cycle

The natural process by which nitrogen from the atmosphere or decomposed organic material is converted by soil bacteria to compounds assimilated by plants, then cycled through organisms and back to the environment.

Nitrogen Fixation

The conversion of atmospheric nitrogen (N2) to ammonia (NH3), carried out by certain prokaryotes, some in mutualism with plants.

Nodules

Swellings on the roots of legumes composed of plant cells containing nitrogen-fixing Rhizobium bacteria.

Bacteroids

A form of the bacterium Rhizobium contained within vesicles formed by root cells in nodules.

Crop Rotation

The practice of growing different crops in succession on the same land to preserve soil productivity.

Mycorrhizae

A mutualistic association of plant roots and fungus.

Ectomycorrhizae

A fungal-plant root association where the fungus surrounds roots but does not penetrate plant cell membranes.

Arbuscular Mycorrhizae

A fungal-plant root association where the fungus invaginates the host plant cell’s plasma membrane; also called endomycorrhiza.

Epiphytes

Plants that nourish themselves but grow on other plants for support, usually on tree branches or trunks.