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Words & Definitions

Crop Rotation

The practice of planting nonlegumes one year and legumes in alternating years to restore concentrations of fixed nitrogen in the soil.


(ep´-uh-fit) A plant that nourishes itself but grows on the surface of another plant for support, usually on the branches or trunks of tropical trees.

Essential Elements

In plants, a chemical element required for the plant to grow from a seed and complete its life cycle, producing another generation in the form of seeds.


(1) The union of haploid gametes to produce a diploid zygote. (2) The addition of mineral nutrients to the soil.


A chemical substance that an organism must obtain in relatively large amounts. See also micronutrient.


An element that an organism needs in very small amounts and that functions as a component or cofactor of enzymes. See also macronutrient.

Nitrogen Cycle, Global

The natural process by which nitrogen, either from the atmosphere or from decomposed organic material, is converted by soil bacteria to compounds assimilated by plants. This incorporated nitrogen is then taken in by other organisms and subsequently released, acted on by bacteria, and made available again to the nonliving environment.

Nitrogen Fixation

The conversion of atmospheric nitrogen (N2) to ammonia (NH3). Biological nitrogen fixation is carried out by certain prokaryotes, some of which have mutualistic relationships with plants.


A swelling on the root of a legume. Nodules are composed of plant cells that contain nitrogen-fixing bacteria of the genus Rhizobium.


An emerging nondestructive biotechnology that seeks to cheaply reclaim contaminated areas by taking advantage of some plant species' ability to extract heavy metals and other pollutants from the soil and to concentrate them in easily harvested portions of the plant.

Sustainable Agriculture

Long-term productive farming methods that are environmentally safe.


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

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