Decomposing organic material that is a component of topsoil.
A mixture of particles derived from rock, living organisms, and decaying organic material (humus).
A soil layer with physical characteristics that differ from those of the layers above or beneath.
The most fertile soil type, made up of roughly equal amounts of sand, silt, and clay.
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.
Long-term productive farming methods that are environmentally safe.
The addition of mineral nutrients to the soil.
A plowing technique that minimally disturbs the soil, thereby reducing soil loss.
An emerging technology that seeks to 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.
A chemical element required for an organism to survive, grow, and reproduce.
A method in which plants are grown in mineral solutions rather than in soil.
An essential element that an organism must obtain in relatively large amounts.
An essential element that an organism needs in very small amounts.
A soil bacterium whose population size is much enhanced in the rhizosphere, the soil region close to a plant’s roots.
The soil region close to plant roots and characterized by a high level of microbiological activity.
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.
The conversion of atmospheric nitrogen (N2) to ammonia (NH3). Biological type is carried out by certain prokaryotes, some of which have mutualistic relationships with plants.
A form of the bacterium Rhizobium contained within the vesicles formed by the root cells of a root nodule.
The practice of planting nonlegumes one year and legumes in alternating years to restore concentrations of fixed nitrogen in the soil.
A mutualistic association of plant roots and fungus.
Association of a fungus with a plant root system in which the fungus surrounds the roots but does not cause invagination of the host (plant) cells’ plasma membranes.
Association of a fungus with a plant root system in which the fungus causes the invagination of the host (plant) cells’ plasma membranes.
A plant that nourishes itself but grows on the surface of another plant for support, usually on the branches or trunks of trees.