Agronomic Glossary

Absorption
In plants, the passing of a compound from one system into another such as water movement from soil into plant roots. In soils, the binding of a chemical into a soil particle.
Acclimation
Physical and physiological processes that prepare plants for temperature extremes.
Acid Injection
In irrigation systems, adding of acidic materials such as sulfur or phosphoric acid to irrigation water with excessive pH, bicarbonate, and carbonate contents. This lowers the pH and converts bicarbonate and carbonate into carbon dioxide and water.
Actinomycetes
Soil microorganisms intermediate between bacteria and fungi.
Activated Sludge
Aerated sludge that is subjected to bacterial processes.
Active Acidity
Acidity of a soil solution from free hydrogen ions measured as pH.
Activity Index
Measurement (index) of the proportion of hot water soluble nitrogen (HWSN) relative to hot water insoluble nitrogen (HWIN) in urea formaldehyde fertilizers.
Adhesion
Molecular attraction and contact between the surfaces of two unlike substances or objects.
Adsorption
Bonding or adhering of ions or compounds to the surface of soil particles or plant parts.
Aerification
In turfgrass, a method of cultivation where hollow or solid tines are inserted into and removed from the turfgrass and soil to control soil compaction and increase water and air penetration. Hollow tine aerificaiton involves using hollow tines that remove soil cores or plugs while solid tine aerification using solid tines and does not remove any soil.
Aerobic
Requiring oxygen or having oxygen present in the environment.
Aggregate
Collected together in tufts, groups, or bunches.
Agronomy
Science of crops and soils.
Alkaline Soil
Soil that has a pH above 7.0.
Alkalinity
The capacity of water to neutralize acids. A property imparted by carbonates, bicarbonates, hydroxides, and others.
Amendment
Any material such as sand, sawdust, gypsum, diatomaceous earth, peat, or calcined clay that is added to soil to alter its chemical and/or physical characteristics.
Amino Acids
Nitrogen containing organic acids that are building blocks to form proteins. Amino acids contain one or more amino (-NH2) groups, a carboxyl group (-COOH), and possibly sulfur.
Ammonification
Conversion of amino acids and other nitrogen containing organic compounds into ammonia (NH3) and ammonium ions (NH4+).
Anaerobic
Not requiring oxygen or the absence of oxygen in the environment.
Anion
Negatively charged ion that is attracted to a positively charged anode.
Atom
Smallest unit of a chemical element that retains its characteristic properties.
Atomic Number
Number of protons in the nucleus of an atom.
Atomic Weight
Weight of an atom of an element relative to the weight of an atom of carbon (12C), which has been assigned the value of 12.
Available Water
Portion of soil water that can be readily absorbed by plant roots. Often considered to be that water held in the soil against a pressure of -33 kPa to approximately -1,500 kPa (or -15 bars).
Bacteria
Microscopic, single cell, non-green organisms with rigid cell walls that reproduce by cell division. Bacteria are prokaryotes.
Base Saturation
The degree to which the cation exchange capacity’s binding or exchange sites are occupied with cations such as calcium, magnesium, sodium, and potassium as opposed to acid cations such as aluminum and hydrogen is referred to as the base saturation of a soil. Soil pH and fertility generally increase as the percentage base saturation increases.
Biodegradation
Breakdown (digestion) by biological organisms.
Buffering Capacity
The ability of a soil to resist chemical changes. The major buffering system for soils is the cation exchange capacity.
Bulk Density
Measurement of soil compaction expressed as a weight per unit of soil (grams per 100 cc).
Calcined Clay
A granular soil modification amendment consisting of highly fired clay minerals such as montmorillinite and attapulgite clays that are absorbent and stable.
Carbohydrates
Plant food sources including sugars and starches containing carbon with hydrogen and oxygen in a 2 to 1 ratio, as in water (H2O).
Carbon-Nitrogen Ratio
Ratio of organic carbon weight to total nitrogen weight in soil or organic material.
Cation
Positively charged ion that is attracted to a negatively charged cathode.
Cation Exchange Capacity
Sum of exchangeable cations a soil can adsorb and retain against leaching and is expressed as centimoles per kg of soil or milliequivalent per 100 grams of soil. Sometimes referred to as the CEC.
Centrifugal Spreader
Machine that spreads granules as they drop onto a spinning disc or blade beneath the hopper.
Chelate
Cyclic structures of a normally non-soluble metal ion and an organic component that, when held together, become soluble in water.
Chlorosis
Yellowing of normally green plant tissue due to chlorophyll loss.
Clippings
Leaf and stem portions of plants severed by mowing.
Cold Water Insoluble Nitrogen (CWIN)
Insoluble nitrogen fertilizer fractions associated with urea reaction fertilizers that are insoluble in cold water (72 F).
Cold Water Soluble Nitrogen (CWSN)
Soluble nitrogen fertilizer fractions associated with urea reaction fertilizers that are soluble in cold water (72 F).
Colloids
Very small particles that are formed during the weathering process of soils.
Compost
Residues from organic matter and soil piles allowed to undergo biological decomposition.
Core Aerificaiton
see Aerification.
Coring
see Aerification
Crown
A meristematic growing point at or just below the ground where stems and roots join and new shoots emerge.
Cultivation
The disturbance of soil and/or thatch layer without destroying the turfgrass (e.g. aerification, slicing, spiking, etc.).
Denitrification
The biological conversion of nitrate or nitrite to gaseous nitrogen as either N2 or N2O.
Dethatching
Removal of excessive turfgrass thatch and/or mat using stiff rakes or a series of vertically mounted knives or tines.
Diatomaceous Earth
Geological deposit of siliceous skeleton material of diatoms (algae).
Effluent
Partially or completely treated waste water from a treatment plant, reservoir, or basin.
Electrical Conductivity (EC)
A measure of salinity using electrical conductance expressed millimhos per centimeter (mmhos/cm) or decisiemens per meter (dS/m).
Electron
A negatively charged subatomic particle which orbits the atom’s positively charged nucleus, determining the atom’s chemical properties.
Element
A substance composed of only one kind of atom. These combine to compose all materials.
Enzyme
A complex organic agent that enhances cellular reaction rates without being altered in the process.
Exchangeable Sodium Percentage (ESP)
A measure of excessive sodium hazard in the soil as the ratio (as percent) of exchangeable sodium to the remaining exchangeable cations (Ca, Mg, and K).
Fertigation
Fertilizing through irrigation systems.
Fertilizer
Any material, except lime, supplying essential nutrients to plants.
Fertilizer Burn
Plant injury from dehydration due to contact with materials containing salts.
Field Capacity
The percentage of water a soil retains against the action of gravity and typically is that remaining in a soil 2 to 3 days after having been saturated and free drainage has occurred. Estimated at -33 kPa water potential.
Foliar Burn
see Fertilizer Burn.
Foliar Feeding
Light liquid fertilizer applications to plant foliage.
Ground Water
Subsurface water in the zone of saturation that moves freely, often horizontal.
Heavy Metals
Metals with densities of 5 mg per meter or greater and include Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Pb, and Zn.
Hot Water Insoluble Nitrogen (HWIN)
Insoluble nitrogen fertilizer fraction associated with urea reaction fertilizers that is insoluble in hot water (212 F).
Humate (humin)
Portion of soil organic matter that is insoluble in dilute alkali.
Humic Acid
Portion of humus that is water insoluble and is extracted from soil with dilute alkali and precipitated upon acidification.
Humus
Relatively stable, dark-colored colloidal soil organic matter containing no recognizable plant parts.
Hydraulic Conductivity
Rate of water flow in soil as imposed by a hydraulic head.
Hydrolysis
Splitting of one molecule by addition of water.
Immobilization
Conversion of an element from the inorganic form to the organic form in microbial or plant tissues. Often used to describe the conversion of nitrate or ammonium into organic forms by soil microorganisms.
Infiltration Rate
Downward movement or entry of water into the soil.
Ions
Electrically charged atoms resulting from the loss of electrons (cations) or gain of electrons (anions).
Leaching
Downward movement of soluble materials through a soil.
Lime
Calcium oxide (CaO) and/or a variety of acid neutralizing materials containing Ca, Mg, or both Ca and Mg.
Limestone
Sedimentary rock composing more than half calcium carbonate (CaCO3).
Liquid Fertilization
Applying nutrients as dissolved fertilizer in solution.
Macronutrient
Nutrients needed in largest amounts (usually 50 mg/kg) for plant growth (e.g. C, N, O, K, Ca, Mg S, and H).
Micronutrient
Elements or nutrients needed in only small amounts (usually less than 50 mg/kg) for plant growth (e.g. B, Cl, Cu, Fe, Mn, and Zn).
Mineralization
Conversion o fan organic form of an element to an inorganic form (e.g. conversion of organic nitrogen to ammonium nitrogen) by microbial decomposition.
Nitrification
Microbial oxidation of ammonium nitrogen to nitrites and eventually to nitrates.
Organic Matter
Residual decomposition of plant or animal content in soil.
Osmosis
Diffusion of water or any solvent (pure liquid) from a region of greater water potential to one of lesser water potential across a selectively permeable membrane.
Osmotic Potential
Change in chemical potential (or free energy) of water produced by solutes being added to it.
Oxidation
Loss of an electron by an atom or molecule where oxygen is the electron acceptor.
Peat
Partially decomposed organic matter accumulating under wet conditions.
Percolation Rate
Downward movement of water through a soil profile.
pH
Degree of acidity or alkalinity. Defined as the negative logarithm of hydrogen ion activity. A scale of 0 to 14 is used where 7 is neutral, below 7 is acidic and above 7 is alkaline.
Sewage Sludge
Settled sewage solids removed by screening, sedimentation, chemical precipitation, or bacterial digestion.
Soil
Upper layer of Earth’s surface used as the natural medium for plant growth.
Solute
A molecule dissolved in a solution.
Thatch
Brown to black colored layer of dead turfgrass plant leaves, stems, rhizomes, crowns, and stolons between the green colored vegetation and the soil surface.