Sustainable Soil Management
ACID RAIN. Atmospheric precipitation with pH values less than about 5.6, the acidity being due to inorganic acids (such as nitric and sulfuric) that are formed when oxides of nitrogen and sulfur are emitted into the atmosphere.
ACIDIC SOIL. A soil that has a pH value less than 7.0.
ACIDITY, ACTIVE. The activity of hydrogen ions in the aqueous phase of a soil. It is measured and expressed as a pH value.
ACIDITY, RESIDUAL. Soil acidity that can be neutralized by lime or other alkaline materials but cannot be replaced by an unbuffered salt solution.
ACTINOMYCETES. A group of bacteria that form branched mycelia that are thinner, but somewhat similar in appearance, to fungal hyphae. Includes many members of the order Actinomycetales.
AEROBIC. A condition identified by the presence of oxygen.
AGGREGATE, SOIL. A mass of fine soil particles held together by clay, organic matter, or microbial gums.Aggregates are part of soil structure.
AGRONOMY. A specialization of agriculture concerned with the theory and practice of field-crop production and soil management. The scientific management of land.
AGRONOMIC NUTRIENT RATE. Amount of nutrients required by a crop for an expected yield after all the soil, water, plant, and air credits are considered. Agronomic rates consider nutrient credits from all soil tests, legumes, manure residuals, and other nutrient credits supplied from any other source.
ALFISOLS. An order in Soil Taxonomy. Soils with gray to brown surface horizons, medium to high supply of bases, and B horizons of illuvial clay accumulation. These soils form mostly under forest or savanna vegetation in climates with slight to pronounced seasonal moisture deficit.
ALKALINE SOIL. A soil that has a pH value greater than 7.0.
ALLUVIUM. A general term for all eroded material deposited by running water, including gravel, sand, silt, and clay.
ALUMINOSILICATE. Class of clay minerals found in soils which are primarily comprised of silicon, aluminum and oxygen that are assembled into sheets of silica tetrahedral and aluminum octahedral.
AMMONIFICATION. Stage of nitrogen cycle in which soil organisms decompose organic nitrogen and convert it to ammonia.
AMMONIUM. A form of nitrogen that is available to plants from fertilizer and organic matter decomposition.
AMMONIUM NITRATE SOLUTION. Non-pressure solution of ammonium nitrate in water; usually standardized to 20 percent nitrogen. Used for direct application or for making multi-nutrient liquid fertilizer.
AMMONIUM PHOSPHATE. A group of phosphorus fertilizer manufactured by the reaction of anhydrous ammonia with superphosphoric acid to produce either solid or liquid fertilizer.
AMMONIUM SULFATE. Fertilizer material with an analysis of 21-0-0. It also contains 24 percent sulfur.
ANDISOLS. An order in Soil Taxonomy. Soils developed from volcanic ejecta. The colloidal fraction is dominated by allophane and/or Al-humus compounds.
ANEROBIC. A condition identified by the absence of oxygen.
ANHYDROUS AMMONIA. Fertilizer in pressurized gas form, made by compressing air and natural gas under high temperature and pressure in the presence of a catalyst. Value is 82-0-0.
ANION. An ion with a negative charge.
ANION EXCHANGE CAPACITY. The sum total of exchangeable anions that a soil can adsorb. Expressed as centimoles of charge per kilogram (cmolc/kg) of soil (or of other adsorbing material, such as clay).
APPLICATION RATE. The weight or volume of a fertilizer, soil amendment, or pesticide applied per unit area.
AQUA AMMONIA. Twenty percent anhydrous ammonia dissolved in water.
AQUIFER. Layers of underground porous or fractured rock, gravel, or sand through which considerable quantities of groundwater can flow and which can supply water at a reasonable rate. May be classified as perched, confined, or unconfined.
ARIDISOLS. An order in Soil Taxonomy. Soils of dry climates. They have pedogenic horizons, low in organic matter, that are never moist for as long as three consecutive months.
AVAILABLE NUTRIENT. A nutrient in a form that a plant can absorb.
AVAILABLE WATER. Portion of water in soil that can be readily absorbed by plant roots.