Below is a list of definitions that pertain to plant nutrition and its related studies.

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Absorption - The process by which a substance is taken into and included within another substance, e.g., intake of water by soil, or intake of gases, water, nutrients or other substances by plants.  Practically all of the fertilizer nutrients and water requirements of plants are absorbed through their roots.  Much of this absorption is through the root hairs that are located near the growing tips of the young roots.  It is believed that simple diffusion and active absorption (energy from living cells) are the processes utilized by plants in their absorption of nutrients.

Acid fertilizer - A fertilizer that causes a decrease in pH (i.e., increased acidity or decreased basicity) when applied to the soil/growing media.  Acidity is primarily due to the application of ammonium, ammonia, and/or urea in the fertilizer.

Acidification - The process of making a substance or solution more acid, i.e., lower in pH.  In irrigation, it refers to adding acid (sulfuric, phosphoric, or nitric acid) to the irrigation water to create a slightly acid 5.8 to 6.2 pH or reduction to a certain level of alkalinity.

Acid Soil - A soil with a pH value below 7.0.
A soil containing more hydrogen ions (H⁺) verses hydroxyl ions (OH-) in the soil solution (active acidity) and held to the surface of soil particles (reserve or potential acidity). Soil pH values are below 7, depending on the concentration of hydrogen ions in the soil solution.
Soils become more acid as a result of leaching of calcium (Ca⁺²), magnesium (Mg⁺²), and potassium (K^-) cations from the topsoil into the subsoil, and through the removal of cations by growing crops, and by nitrification of ammonium (NH₄⁺ ) nitrogen.  As cations are removed from the soil particles, they are replaced with hydrogen and acid-forming aluminum ions.  Soil acidity affects availability of essential plant nutrients.

Acidity and basicity of fertilizers - Fertilizers have neutral, acidic (lower soil pH), or basic (increased soil pH) effects when added to the soil.  This effect is commonly expressed in terms of the amount of pure calcium carbonate that would be required to either offset the acid-forming reactions of 100 pounds of fertilizer materials or the amount of calcium carbonate required to equal the acid-neutralizing effects of 100 pounds of fertilizer.

Actinomycetes - A category of soil bacteria that includes thread-like microorganisms forming  elongated cells with a tendency towards branching. Actinomycetes are heterotrophic bacteria utilizing fixed carbon sources and their presence is therefore conditioned by the availability of organic substrates (organic matter).  Their activities aid the decomposition of certain disease resistant components of plant and animal tissue, formation of humus, and organic transformations at high temperatures, particularly in the rotting of green manures, hay, compost piles and animal manures.

Activated alumina - An oxide of aluminum used in water treatment to remove impurities, such as fluoride.

Activated carbon - A form of carbon used in water treatment to remove impurities, such as fluoride.

Activated Sewage Sludge - An organic fertilizer made from sewage, free from grit and coarse solids, and aerated after being inoculated with micro-organisms.  The resulting flocculated organic matter is withdrawn from tanks, filtered with or without the aid of coagulants, dried, ground and screened.

Active Acidity - The hydrogen ion concentration of the soil solution is designated as active acidity.
Active acidity is measured by soil pH but does not indicate the actual magnitude of lime that is required to correct soil acidity.  Lime requirements are based on the amount of reserve or potential acidity held on the soil's exchange complex. See Also: Acid Soil; Reserve Acidity .

Adjusted sodium adsorption ratio (Adj. Rna) - A mathematical term used to estimate the sodium hazard in irrigation water.  It is an equation that takes into account the sodium content of water in relation to the salinity, calcium, magnesium, and bicarbonate content. Similar measures of sodium hazard that are reported are: sodium absorption ratio (SAR), adjusted sodium absorption ratio (SARadj), exchangeable sodium percentage (ESP), sodium percentage, and residual sodium carbonate.

Adsorption - The increased concentration of molecules or ions at a surface, including exchangeable cations and anions on soil particles.

Aeration Soil - The exchange of air in soil with air from the atmosphere.  The composition of the air in a well-aerated soil is similar to that in the atmosphere; in a poorly aerated soil, the air in the soil is considerably higher in carbon dioxide and lower in oxygen than the atmosphere above the soil.

Aerial Shoots - An aerial stem may grow upright, climbing or in a prostrate position.

Aggregate - A group of soil particles cohering so as to behave mechanically as a unit.

Air porosity or air space - The percent volume (volume/volume) of soil/growing media that is filled with air when irrigating media to container capacity.  The air in media is primarily in the large macropores.

Alkaline - A basic reaction in which the pH reading is above 7.0, as distinguished from acidic reaction, in which the pH reading is below 7.0.

Alkaline - Indicates a pH above 7.0.  Alkaline is also called basic.

Alkaline Soil - A soil having a high degree of alkalinity (pH 8.5 or higher) or high in exchangeable sodium (15% or higher) - or both, so that growth of most crops is reduced. A soil having a pH greater than 7.0: practically, one having a pH above 7.3.

Alkaline Soil/Media - A soil/media that has an alkaline reaction, i.e., a soil for which the pH reading of the saturated soil paste is above 7.0.

Alkaline Solution - Aqueous solution of base.

Alkalinity - A measure of water's capacity to neutralize acids.  True alkalinity is the sum of the dissolved bicarbonates, carbonates, hydroxides, ammonia, borates, organic bases, phosphates, and silicates in the water.  Most of the time in practice, alkalinity is the sum of the bicarbonates and carbonates (total carbonates) expressed as me/1 or ppm.

Alakali Soil/Media - See Sodic Soil/Media.

Alum - Either aluminum sulfate [Al₂(SO₄)₃ ·18H₂O] or a double salt of potassium aluminum sulfate [KAl(SO₄)₂·(12H₂ O)] used to treat irrigation water and recycled water to flocculate and remove colloidal clay.  Aluminum sulfate is more commonly used because of its lower costs and its availability in both liquid and dry forms.

Amendment - Any material, such as lime, gypsum, sawdust or synthetic conditioners, that is worked into the soil to make it more productive.  Strictly, a fertilizer is also an amendment, but the term amendment is used more commonly for added materials other than fertilizer.

Amino Acids - Nitrogen-containing organic compounds, large numbers of which link together in the formation of the protein molecule.  Each amino acid molecule contains one or more amino (-NH₂ ) groups and at least one carboxyl (-COOH) group.  In addition, some amino acids (cystine and methionine) contain sulfur.

Ammonia - A form of inorganic nitrogen (NH₃ ).  It can be toxic at concentrations as low as 2.5 p.m. (0.15 mM).  Toxicity increases as pH increases above pH 7.3.

Ammoniacal - Consisting of, containing, or producing ammonia.  When referring to a fertilizer, it indicates a fertilizer that contains ammonia or ammonium (such as ammonium upon breakdown such as urea).

Ammoniated Superphosphate - A product formed by ammoniating superphosphate.

Ammoniation - A process wherein ammonia (anhydrous, aqua or a solution containing ammonia and other forms of nitrogen) is used to treat superphosphate to form ammoniated superphosphate, or to treat a mixture of fertilizer ingredients (including phosphoric acid) in the manufacture of a multinutrient fertilizer.

Ammonification - Formation of ammonium compounds or ammonia. The conversion of organic nitrogen to ammonium-nitrogen by microorganisms in the soil.

Ammonium - An inorganic nitrogen fertilizer (NH₄⁺ ).  Ammonium will always contain a small amount of ammonia in equilibrium.

Ammonium Citrate [(NH₄)₃C₆H₅O₇] - A salt formed ammonia and citric acid.  A neutral ammonium citrate solution, prepared by the official methods of the AOAC, is used as a reagent in the determination of "available" phosphoric acid in fertilizers.  After a sample is washed with water to remove the water-soluble phosphoric acid (P₂O₅), the residue is treated with the neutral ammonium citrate solutions, as prescribed by the official methods, and the phosphoric acid removed by this extraction is termed "citrate-soluble".  The sum of the water-soluble plus the citrate-soluble phosphoric acid is termed "available."

Analysis - Investigation of chemical compound and determination of its composition. The percentage composition as found by chemical analysis, expressed in those terms that the law requires and permits.  Although "analysis" and "grade" sometimes are used synonymously, the term "grade" is applied only to the three primary plant foods - nitrogen (N), available phosphate (P₂O₅) and potash (K₂O) - and is stated as the guaranteed minimum quantities present.  (See also Grade ).

Anchorage - Another function of roots is to hold the stem part of the plant upright.  This anchorage role may be carried out by the regular roots or by special brace roots.

Animal Manures - The excreta of animals - dung and urine with the straw or other materials that may have been used in the confinement areas. The plant nutrients in animal waste solids must usually be mineralized before those nutrients are available to plants.  Nutrients in urine, on the other hand, are immediately available.  Most of the urinary nitrogen is present as urea.  Potassium in both solids and urine is readily available. It is difficult, if not impossible, to control the amount or the timing of N release from animal manures.  This difficulty with manures actually increases the environmental risk, compared to that of commercial fertilizer, when they are used as the primary source of plant nutrients.

Anion - Negatively (electrically) charged particle, e.g., NO₃^- (nitrate ion), HPO₄^2- (hydrogen phosphate ion). A negatively charged ion.

Anion exchange resin - A positively charged ion exchange resin that removes anions (negatively charged ions) from water.

Atom - Smallest particle of chemical element.

Annual - Horticulturally, a plant that completes its entire life cycle in a single growing season.

Antagonism - When one nutrient in high concentration suppresses the activity or another nutrient and causes an induced nutrient deficiency.

Apatite - (rock phosphate) - A mineral phosphate having the type formula Ca₁₀(X₂) (PO₄)₆ where X is usually fluorine, chlorine or the hydroxyl group, either singly or together.  Fluorapatite is widely distributed as the crystalline mineral and as amorphous phosphate rock, both forms of which are important fertilizer materials.  Crystalline fluorapatite contains from 38.0 to 41.0 percent phosphoric acid (P₂O₅) and from 3.2 to 4.3 percent fluorine.  Calcium hydroxyapatite or calcium hydroxy-phosphate, Ca₁₀(OH)₂(PO₄)₆ , may be formed to a small extent in ammoniated superphosphate.

Arboriculture - Cultivation of woody plants, particularly those used for decoration and shade.

Artificial Media - A mixture of various organic and inorganic constituents, such as perlite, vermiculite and peat moss, but not including soil, which is used for growing plants in containers or beds.

Assimilation - The process of assimilation is the absorption and incorporation of nutrients into the cell protoplasm.  This process can take place in any cell which has growth or manufacturing function.  It is especially active in the leaf and root cells.

Atomic weight - Weight of atom, referred to weight of hydrogen atom.

Autotrophic Bacteria - A category of soil bacteria that obtain their energy from the oxidation of mineral constituents, such as ammonium, sulfur, and iron and obtain most of their carbon from carbon dioxide. The numbers of these bacteria are much smaller than those classified as heterotrophic but their involvement in nitrification and sulfur oxidation reactions makes them tremendously important in higher plant nutrition.

Available - In general, a form capable of being assimilated by a growing plant.  Available nitrogen is defined as the nitrogen that is water-soluble plus what can be made soluble or converted into free ammonia.  Available phosphoric acid is that portion which is water-soluble plus the part which is soluble in ammonium citrate. Available potash is defined as that portion soluble in water or in a solution of ammonium oxalate.

As applied to nitrogen, phosphorus, and potassium, this term has somewhat different meanings.  In each case all that is soluble in water is available.  In addition, however, some of each that is not soluble in water is available to plants.  In general, a form of nutrient capable of being assimilated by a growing plant. Available nitrogen is defined as nitrogen that is water-soluble plus that which is readily solubilized or converted to free ammonia.  Available phosphorus (expressed as P₂O₅) is that portion which is water-soluble plus that which is soluble in ammonium citrate.  Available potassium (expressed as K₂ O) is defined as that portion soluble in water or a solution of ammonium oxalate.

Available Nutrient in Soil/Media - The part of the supply of a plant nutrient in the soil that can be taken up by plants at rates and in amounts significant to plant growth.

Available water capacity (AWC) - The percent volume (volume/volume) of soil/growing media occupied by water that is available to the plant.  It is calculated by determining the container capacity, then subtracting the unavailable water (PWP).

Available Water in Soil/Media - The part of the water in the soil that can be taken up by plants at rates significant to their growth; usable; obtainable.

Bagasse - An organic growing media component made from sugar cane fiber.

Banded Fertilizer - Placement of fertilizer in a concentrated zone either on or below the soil surface.
Concentrated zones or bands of fertilizer tend to minimize fixation of added nutrients by the soil or crop residues and make the fertilizer more available to plant roots.

Banding - Method of fertilizer application.  Banding is a general term that implies applications which concentrate fertilizers into narrow zones that are kept intact to provide a concentrated source of nutrients.  Applications may be made prior to, during, or after planting. See Also: Deep Banding Fertilization; Dribble Fertilization; Starter Fertilizer .

Bark - An organic growing media component made from the bark of hardwood or softwood trees.  It is usually hammer milled, screened to size, and composted or aged prior to use.

Base - Compound that forms hydroxide ions (OH^-) in aqueous solutions, in a wider sense also metals, e.g., K, Ca (see alkaline solution ).

Base Exchange - The replacement of cations, held on the soil complex, by other cations.  (See also Cation Exchange Capacity )

Basic - Indicates a pH above 7.0.  Basic is also called alkaline.

Basic fertilizers - A fertilizer that causes an increase in pH (i.e., decreased acidity or increased basicity) when applied to soil/growing media.  A fertilizer is basic primarily due to its nitrate content.

Basic Slag - A by-product in the manufacture of steel , containing lime, phosphate and small amounts of other plant food elements such as sulfur, manganese and iron.  Basic slags may contain from 10 to 17 percent phosphate (P₂O₅ ), 35 to 50 percent calcium oxide (CaO) and 2 to 10 percent magnesium oxide (MgO).  The available phosphate content of most American slag is in the range of 8 to 10 percent.

Basic Soil/Media - See Alkaline Soil/Media .

Best management practices (BMP) - The practice of minimizing production inputs that contribute to environmental contamination. :  Best management practices (BMPs) are those practices which have been proven in research and tested through farmer implementation to give optimum production potential, input efficiency, and environmental protection.

Bicarbonate - Partially dissociated carbonic acid in the form HCO₃^- .  A water pH between 7.4 and 9.3 will have bicarbonate as the main form of carbonic acid present.

Bonemeal - Raw bone meal is cooked bones ground to a meal without any of the gelatin or glue removed.  Steamed bone meal has been steamed under pressure to dissolve out part of the gelatin.

Boom system - An overhead irrigation system where the nozzles are mounted on a boom that moves above the plants.

Boron (B) - Boron (B) is an essential non-metallic micronutrient and exists in the soil in a number of primary and secondary nutrients.  It is absorbed by plants as boric acid (H₂BO₃ ) or one of the borate anions.Boron is essential for germination of pollen grains and growth of pollen tubes and is essential for seed and cell wall formation.  Boron forms sugar/borate complexes associated with sugar translocation and effects protein formation.  Boron deficiency generally results in stunted plant growth - the growing point and the younger leaves first because of lack of mobility in the plant.  In many crops the symptoms of boron deficiency are well defined and quite specific such as crooked and cracked stem in celery, corky core in apples, black heart in beets, hollow heart in peanuts, and ringed or banded leaf petioles in cotton.  Alfalfa, especially susceptible to boron deficiency, shows a rosetting (yellow top), then death of the terminal bud.  Coarse-textured sandy soils low in organic matter are typically low in minerals that contain boron and boron availability.  Organic matter is an important source of soil boron.  High soil pH also limits boron availability.  Deficiencies of this element can be determined by soil and plant analysis.

Brand - The trade name assigned by a manufacturer to a particular fertilizer product.

Brimstone - Sulfur.

Brine water - A water very high in solutes.  It may also refer to the byproduct or waste water of water purification systems.

Broadcast Application - Application of either solid or fluid fertilizer to the soil surface with or without subsequent incorporation by tillage.  No specific location relative to the plant is implied.  Nutrients may be applied prior to or after the crop is planted. See Also: Weed-and-Feed; Top-Dressed Application .

Buds (Herbaceous) - The growth of herbaceous stems is largely from buds which are a mass of meristematic tissues that develop into branches from nodes or joints on the main stem.  They are mostly naked buds and not covered with scales for protection.  Herbaceous buds may develop into stems, leaves or flowers.

Buds (Woody) - The elongation growth of woody stemmed plants is from buds.  Also they develop in the axils of leaves, junction of leaves and twigs, ends of branches and at nodes.  However, in woody plants the secondary growth or cambium tissues cover up the nodes of the young elongating stems.  Woody stemmed buds are usually covered with scales for protection.

Buffer - A system of substances, usually a mixture of weak acids and their salts, which tends to resist changes in pH.  In soils, organic matter, clays, and free calcium carbonate tend to buffer the system against pH changes.

Buffer Capacity of Soil - The ability of a soil to resist a change in soil solution hydrogen ion concentration (soil pH), resisting the tendency to become more acid upon the addition of an acid or an acid-forming material or more alkaline upon addition of basic materials such as lime. The ability of the soil to resist a change in its pH (hydrogen ion concentration) when acid-forming or base-forming materials are added to the soil.

Builder's lime - See hydrated lime .

Bulbs - A few plants, such as the tulip, have bulbs very similar to the onion except all of the bulb portion of the stem is below the ground.

Bulk Blending - The practice of mixing dry, individual, granular materials or granulated bases.  The product is a mixture of granular materials rather than a granulated mixture.

Bulk density - The ratio of the mass (weight) of dry soil/growing media to its bulk volume, expressed as grams per cubic centimeter (g/cc) or pounds per cubic foot (lb/cu ft).

Bulk Density - The ratio of the mass of water-free soil to its bulk volume.  Bulk density is expressed in pounds per cubic foot or grams per cubic centimeter and is sometimes referred to as apparent density.  When expressed in grams per cubic centimeter, bulk density is numerically equal to apparent specific gravity or volume weight.

Calcareous Soil - A soil containing calcium carbonate, a soil alkaline in reaction because of the presence of free calcium carbonate.
Properties:  Treatment with dilute hydrochloric acid causes such soils to effervesce (fizz), giving off carbon dioxide gas. A soil containing calcium carbonate, or a soil alkaline in reaction because of the presence of calcium carbonate; a soil containing enough calcium carbonate to effervesce (fizz) when treated with dilute hydrochloric acid.

Calcareous soil - A field soil containing large amounts of free calcium carbonate (i.e., lime), usually with a high pH of 7.6 to 8.3.  Common in the southwestern states and areas of low rainfall.

Calcined clay - An inorganic growing media component made from clay that is fired (calcined) to harden it, then crushed and screened to size.

Calcitic lime - A lime composed of calcium carbonate (CaCO₃ ) derived from calcite.  Pure calcitic lime contains 40% Ca.  It is also called calcitic limestone.

Calcium (Ca) - Calcium (Ca) is an essential secondary nutrient grouped with sulfur (S) and magnesium (Mg).  It exists in the soil and is absorbed as the Ca⁺² ion. Calcium stimulates root and leaf development and forms compounds which are part of the cell walls.  Physiological roles include the activation of several enzyme systems, reduction of nitrate, and neutralization of organic acids.  Calcium deficiency symptoms are not often seen in the field because secondary effects, associated with high soil acidity, limit growth first.  Leaves may be cupped-shaped and crinkled, and the terminal buds deteriorate with some breakdown of petioles.  Fruits may break down at the blossom end.  Calcium deficiency is associated with "blossom-end rot" in tomatoes and other crops.  Deficiencies can be determined by soil and plant analysis.

Calcium carbonate (CaCO₃ ) equivalent - On fertilizer labels it is used as the basis for expressing potential acidity (how much calcium carbonate could 1 ton of the

Calcium Carbonate Equivalent - The amount of calcium carbonate required to neutralize the acidity produced by a given quantity of fertilizer product.

Cambium Section of the Root - As the root increases in diameter, meristematic tissue develops between existing xylem and phloem tissues.  These meristematic tissues are responsible for and are called cambium.

Capillary action - Absorption and movement of water through capillary pores due to the forces of capillary attraction.  Water from subirrigation systems and some drip systems wet growing media by capillary action.

Capillary mat irrigation system - A subirrigation system where container plants are placed on a moistened mat or absorbent material from which water moves into the container by capillary action.

Carbohydrate - A compound containing carbon, hydrogen and oxygen.  Usually the hydrogen and oxygen occur in the proportion of 2 to 1, such as in glucose (C₆H₁₂O₆ ).

Carbonate - Completely dissociated carbonic acid in the form CO₃⁼ .  At pH 10.3 or above, carbonate is the predominate form present.

Carbonic acid - Dissolved carbon dioxide in the hydrated form H₂CO₃ .  At pH of 6.4 or below, carbonic acid is the predominate form present.

Carbon Cycle - The cycling of carbon in the environment including the fixation of atmospheric carbon dioxide (CO₂ ) by plants in the presence of sunlight and water to form sugar (photosynthesis), conversion of sugars to plant structural components, consumption of plants by man and animals, and the return of carbon dioxide to the atmosphere by decay of plant and animal residues.

Carbon:Nitrogen Ratio - The ratio obtained by dividing the percentage of organic carbon by percentage of nitrogen.

Cation - A positively charged ion. An ion carrying a positive charge of electricity.  Common soil cations are calcium, magnesium, sodium, potassium and hydrogen. Positively (electrically) charged particle, e.g., K⁺ (potassium ion), Mg²⁺  (magnesium ion), NH₄⁺ (ammonium ion). A charged form of an atom or molecule carrying one or more position charges of electricity (valence). The most common soil cations are calcium (Ca⁺²), magnesium (Mg⁺²), sodium (Na⁺), potassium (K⁺), ammonium (NH₄⁺), and hydrogen (H⁺) and aluminum (Al⁺³).

Cation Exchange - The exchange of cations held (adsorbed) at the surface of soil clay and organic matter particles for other cations in the soil solution.  Cation exchange is an important reaction in soil fertility, in correcting soil acidity and alkalinity, in changes altering soil physical properties and as a mechanism in purifying or altering percolating waters.  For example, when an acid soil high in exchangeable hydrogen ions is treated with a liming material such as calcium hydroxide (Ca(OH)2), calcium ions from the lime replace hydrogen ions at the surface of the soil particles.  The hydrogen ions are neutralized by hydroxyl ions and soil pH increases. The plant nutrients calcium (Ca), magnesium (Mg), and potassium (K) are supplied to plants in large measure from exchangeable forms.  The usual soil test to predict a soil's ability to furnish potassium to the plant is a measure of the soil's exchangeable potassium content.  The amounts of cations in the soil solution are intimately related to the exchangeable ions.  Any change in the concentration of cation in the soil colloids.  Cation exchange capacity (CEC) is the amount of exchangeable cations per unit weight of soil (dry basis).

Cation exchange capacity (CEC) - The milliequivalents (1/1000's of an equivalent) of cation exchange sites present per 100 grams (me/100 g) of dry soil. In soilless organic-based growing media, it is often expressed as milliequivalents per 100 cubic centimeters (me/100 cc)  because of the very low weight of dry soilless media.  The CEC is a measure of the nutrient holding capacity of cationic nutrients, such as K⁺, NH₄⁺, Ca⁺⁺ , etc. The total quantity of cations which a soil can adsorb by cation exchange, usually expressed as milliequivalents per 100 grams.  Measured values of cation exchange capacity depend somewhat on the method used for the determination.

Cation exchange resin - A negatively charged ion exchange resin that removes cations (positively charged ions) from water.

Cation Exchange Sites - Locations of the surface of soil colloids (clay, organic matter) with negative charges capable of attracting and holding positively charged cations. Cations exchange sites are more abundant in fine soils having high contents of clay and organic matter than in sandy soils that are low in clay and organic matter.  Divalent cations such as calcium (Ca⁺²) are held more firmly at the surface of soil colloids than monovalent cations such as potassium (K⁺ ).

Cell Structure - Most plant cells contain three major parts: the cell wall, protoplasm and inclusions.

Cellulose acetate-type membranes - A membrane composed of cellulose acetate used in reverse osmosis water purification systems.  These membranes are sensitive to pH, but resistant to chlorine.

Cell Wall - A cell wall consists of cellulose or lignin-like material which may be covered with a gelatinous pectin and/or waxy substance.  Also, it may be impregnated with oils and resins.  The cell wall gives form and support to the plant tissue.  It encloses and protects the living substances, or protoplasm, inside the cell.  There may be thin areas (pits) and perforations in a cell wall through which fluids, salts, protoplasmic strands, etc., move to an adjacent cell.

Chelate - Derived from the Greek word "chele" meaning claw.  A large organic molecule, called  a chelating agent, that contains one of the micronutrient heavy metals - iron (Fe), zinc (Zn), manganese (Mn), copper (Cu)-or divalent cations-calcium (Ca), magnesium (Mg)-held in the center by ligand bonds.  Used as fertilizers in alkaline soil/media/water to keep Fe, Zn, Mn, and Cu soluble.

Chelates - Certain organic chemicals, known as chelating agents, form ring compounds in which a polyvalent metal is held between two or more atoms.  Such rings are chelates.  Among the best chelating agents known are ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA) and diethylenetriaminepentaacetic acid (DTPA).  Citric acid is also used as a chelating agent.

Chelating agent - A large organic molecule that is able to bond to heavy metal micronutrients-  iron (Fe), zinc (Zn), manganese (Mn), copper (Cu),- or divalent cations-calcium (Ca), magnesium (Mg)-by ligand bonds to form a chelate.  The most commonly used chelating agents in fertilizers are DTPA, EDDHA, HEDTA, EDTA, citrate, and lignosulfonates.

Chemigation - Application fertilizers and/or pesticides in irrigation water to fertilize crops and control pests. Application of fertilizer, particularly nitrogen, in irrigation water is an accepted means of application close to the time of plant need.  Sulfur can also be easily applied in this manner.  This technique is also known as fertigation.   Herbicide and insecticide application through sprinkler irrigation systems can be an effective means of pest control.  Special precautions are required to prevent fertilizers and pesticides from siphoning into the well.
See Also: Fertigation .

Chemoautotrophic Bacteria - Microorganisms are divided into two broad classes with respect to their energy and carbon sources: heterotrophic forms which require preformed organic nutrients to serve as sources of energy and carbon, and autotrophic microorganisms, which obtain their energy from sunlight or by the oxidation of inorganic compounds and their carbon by the assimilation of carbon dioxide.  Autotrophic bacteria are of two general types: photoautotrophs , whose energy is derived from sunlight, and chemoautotrophs, which obtain the energy needed for growth and biosynthetic reactions from the oxidation of inorganic materials.Some species of bacteria are limited exclusively to inorganic oxidations and are considered to be obligate chemoautotrophs.  Significant obligate chemoautotrophs include the genus Nitrosomonas, which oxidizes ammonium nitrate to nitrite; Nitrobacter, which oxidizes nitrite-nitrogen to nitrate; and Thiobacillus, which oxidizes certain inorganic sulfur compounds.

Chlorination - To treat with chlorine as a disinfectant; used in recycled water treatment.

Chlorine (Cl) - Plants utilize this non-metallic micronutrient in the form of chloride (Cl^- ), the only form in which this element exists in the soil. Chloride is involved in energy reactions in the plant, specifically involved in the chemical breakdown of water in the photosynthesis reaction.  It also activates several enzyme systems.  It is involved in transporting several cations - potassium, calcium, magnesium - within the plant, regulating the actions of stomatal guard cells, thus controlling water loss and moisture stress while maintaining plant turgor.  Research has shown that chloride diminishes the effects of fungal root and leaf diseases in small grains.  Lowered incidence of stalk rot in corn has been related to adequate chloride.  Chloride is very mobile in the soil and leaches readily.  Deficiencies are most likely on sandy soils but can occur on any soil texture.  Deficiencies can be determined by soil and plant analysis.

Chloroplast - The green plastids contain chlorophyll and are called chloroplasts.  The chloroplasts are the food-making bodies of the protoplasm of plants.  These green bodies have the ability to capture, hold and utilize the energy of the sun (it is not known just how this function is carried out) in the synthesis of the many plant chemical compounds.

Chlorosis - Loss of the green color in plants indicated by yellowing of the leaves. A sign of nutrient deficiency.  Specific patterns of chlorosis are characteristic of individual nutrients. Pale green to yellow coloration.  The term is usually applied to leaves and is a common symptom of many nutrient deficiencies. Yellowing of green portions of a plant, particularly the leaves.

Chromoplast - The red, yellow and orange plastids are called chromoplasts.  They contain zanthophyll and carotene and give color to flowers and fruits.

Citrate - A organic acid that is sometimes used as a micronutrient chelating agent of iron, zinc, copper, and manganese.  Citrate possesses weak chelating ability.

Citrate-Soluble Phosphoric Acid - That fraction of the phosphoric acid insoluble in water but soluble in neutral ammonium citrate.  However, since that soluble in water is also soluble in ammonium citrate, "citrate-soluble" may be used to indicate the sum of water-soluble plus citrate-soluble phosphoric acid.  (See also Available .)

Clarified water - Partially purified water free of heavy sediments and floating debris.

Clarifier - A pit, basin, or tank for removing colloidal material in water treatment systems. Chemicals are added to flocculate the colloidal material, then polymers are added to aggregate the floc and cause it to settle to the bottom.  The clear water is then recovered from the top layer.

Clay - A minute soil particle less than 0.002 millimeter in diameter. Naturally occurring inorganic crystalline particles in soils and other parts of the earth's crust.  Clay particles are less than 0.002 millimeters in diameter. Properties:  Contains compounds of silicon, aluminum, hydrogen, and oxygen.

Climbing Stems - Some plants have their stems and branches encircle or twine around an upright object, as a post or tree, for an upright support.  The pole bean and morning glory vines are examples of climbing stem plants.

Coagulant - A chemical that causes flocculation, such as alum which acts as a coagulant to flocculate colloidal clay.

Coated Fertilizers - Fertilizer materials, generally urea, that are coated to slow the release of the fertilizer.  Coating material is most commonly sulfur, but resins and thermoplastics are also used.

Coefficient of uniformity (Q) - A measure of how uniformly an irrigation system delivers water, with 1 being perfect and below 0.8 indicating a poorly performing system.

Coir fiber - An organic growing media component made from coconut husk fiber.

Collenchyma - Another strengthening stem tissue similar to the sclerenchyma tissue is the collenchyma tissue.  It is composed of thick-walled cells which have thickened corners.  The collenchyma cells stay alive longer than the sclerenchyma tissue cells.

Colloid - Soil particles (organic or inorganic) having small diameters ranging from 0.10 to 0.005 micron. Characterized by high cation exchange capacity.  Colloids have a vast surface area per unit mass, which accounts for their high adsorptive capacity and their high cation exchange capacity in soils.

Colloidal solution - Mixture of very fine solid particles with liquid (e.g., protein colloid), either in liquid (sol) or jelly-like state (gel).

Complete Fertilizer - A fertilizer containing all three of the primary fertilizer nutrients (nitrogen, phosphate and potash) in sufficient amounts to be of value as nutrients.

Complex Group - The complex plant groups have a more complex or advanced stage of development and are found mostly on land.  They have much more complex structure, including conducting tissue and embryos.  The seed producing plants of this group dominate the vegetative production found on the earth's land mass.  Also they provide most of the food and fiber for man.

Complex Permanent Tissues - When a permanent tissue is composed of several kinds of cells which make simple tissue, they form a complex permanent tissue.  The two important complex permanent tissues are xylem and phloem.

Compost - A mixture that consists largely of decayed organic matter and is used for fertilizing and conditioning soil.
A mixture that consists largely of decayed, relatively stable plant and animal wastes. Used for fertilizing and conditioning the soil.

Composting - A process that partially decomposes organic matter.

Compound - Substance consisting of several elements, e.g., water (H₂ O).

Conditioner (of fertilizer) - A material added to a fertilizer to prevent caking and to keep it free-flowing.

Conditions for Photosynthesis - The direct conditions necessary for photosynthesis are: carbon dioxide (from air), water (mostly from roots), favorable temperature (5 to 40 C or 40 to 105 F), light or energy from the sun (only about 3 to 5% of the sunlight energy is utilized by the leaves) and chlorophylls (the green pigments in the chloroplasts).

Conductivity, Electrical - A physical quantity that measures the readiness with which a medium transmits electricity.  Commonly used for expressing the salinity of irrigation waters and soil extracts because it can be directly related to salt concentration.  It is expressed in decisiemens per meter (dS/ m), or in millisiemens per centimeter (mS/ cm) or millimhos per centimeter (mmhos/ cm), at 25°C.

Conductivity meter - An instrument used to measure electrical conductivity of solutions.  Also called a solubridge or salts meter.

Conservation Tillage - Any tillage system that maintains at least 30 % of the soil surface covered by residue after planting to reduce soil erosion by water; or where soil erosion by wind is the primary concern, maintains at least 1000 pounds of flat small grain residue equivalent on the surface during the critical wind erosion period. Many different types of tillage systems can be used to meet the requirements of this .   Emphasis should be placed on the achievement of the desired goal and development of a systematic approach to that goal.  There is no reason to replace or eliminate a piece of equipment from a tillage system if it is helping to achieve the goals established for that field.  Several specific types of tillage systems are included under the general heading of conservation tillage.  These terms include:
   No-till: The soil is left undisturbed from harvest to planting except for nutrient injection.  Planting or drilling is accomplished in a narrow seed bed or slot created by coulters, row cleaners, disk openers, in-row chisels or roto-tillers.  Weed control is accomplished primarily with herbicides.  Cultivation may be used for emergency weed control.  In addition to deep placement of nutrients, starter fertilization is advisable and widely practiced.  Side-dressed nitrogen for row crops and top-dressed nitrogen for small grains with dribble techniques may improve use efficiency.  Fertigation is an option.
  Ridge-till: The soil is left undisturbed from harvest to planting except for nutrient injection.   Planting is completed in a seedbed prepared on ridges with sweeps, disk openers, coulters or two cleaners. Residue is left on the surface between ridges.  Weed control is accomplished with herbicides and/or cultivation.  Ridges are rebuilt during cultivation.
Methods of fertilizer application include knife placement into the ridge prior to planting use of starters, side-dressed applications and fertigation.
   Mulch-till : The soil is disturbed prior to planting.  Tillage tools such as chisels, field cultivators, disks, sweeps or blades are used.  Weed control is accomplished with herbicides and/or cultivation.  Fertilizer application methods include broadcast applications; knifed applications with tillage equipment including sweeps; starter application; side-dressing; top-dressing, and fertigation.

Container capacity - The percent volume (volume/volume) of soil/growing media filled with water after it has been saturated and allowed to drain.  It is sometimes called the water holding capacity and is the maximum amount of water that soil/growing media can hold.  In field soils, it is called field capacity.

Container Stock - Nursery plants grown entirely in containers rather than being dug from a field.

Controlled-release fertilizer (CRF) - A fertilizer that is not immediately soluble and available to plants because the nutrients are released over time, from weeks to months.  Release is based on low solubility, biological breakdown, or a semipermeable coating.

Controlled-Release Fertilizer - "Slow or Controlled Release Fertilizers.  A fertilizer containing a plant nutrient in a form which delays its availability for plant uptake and use after application, or which delays its availability to the plant significantly longer than a reference 'rapidly available nutrient' fertilizer such as ammonium nitrate or urea, ammonium phosphate, or potassium chloride.  Such delay of initial availability or extended time of continued availability may occur by a variety of mechanisms.  These include controlled water solubility of the material (by semipermeable coatings, occlusion, or by inherent water insolubility of polymers, natural nitrogenous organics, protein materials, or other chemical forms), by slow hydrolysis of water-soluble low molecular weight compounds, or by other unknown means."  (AAPFCO).  Also called controlled-availability fertilizers and slow-release fertilizers. Limited solubility may be an inherent characteristic of the fertilizer such as in urea-formaldehyde reaction products and magnesium ammonium phosphate; or it may be imparted to a soluble fertilizer by coating the particles with such materials as molten sulfur, waxes, and plastics.

Conventional Agriculture - Conventional agriculture is composed of modern, site-specific, progressive, science-based production systems in which available and applicable technologies and inputs are used effectively and efficiently.  Conventional agriculture shows concern for the environment as well as profitability. Production systems have developed over time because they are more efficient and profitable.  Today's conventional systems are the results of extensive research and education programs on the development, adaptation, and implementation of technology in production practices in a competitive system.  Any inefficient, resource-wasting practices are constantly being eliminated and replaced with more efficient, best management practices (BMPs).

Conventional Tillage - Conventional tillage systems vary widely from region to region and crop to crop.  The term conventional tillage originally implied use of the moldboard plow, disking, and harrowing to level the soil surface prior to seeding.  In actuality, however, conventional tillage systems have now evolved to the use of other tillage implements including widespread use of the chisel plow or other primary tillage implements.  Conventional tillage today is actually a reduced tillage system compared to past practices.

Copper (Cu) - Copper (Cu) is an essential metallic micronutrient and is absorbed by plants from the soil in the form of the Cu⁺² ion. copper is necessary for chlorophyll formation in plants and catalyzes several other plant reactions although it is not usually a part of the products formed by those reactions.  Organic soils are most likely to be copper deficient, since copper is fixed in unavailable forms in these soils.  High soil pH also decreases copper availability.  Mobility in the plant is low.  Common symptoms of copper deficiency include dieback in citrus and blasting of onions.  Leaves of copper-deficiency vegetable crops lose turgor and develop a bluish-green shade before becoming chlorotic and curling.  Plants may fail to flower.  Small grains fail to develop heads when copper is deficient.  Deficiencies of this element can be determined by soil and plant analysis.

Cork - Another protective simple tissue is cork.  This tissue is composed of cells which have their walls water-proofed by suberin.  Since the function of this tissue is to protect the inner tissue from excessive evaporation or a physical protection, their cells die shortly after they are formed.  Tree bark and the skins of many tubers are examples of cork tissue.

Corms - Other plants, such as a crocus, have a globose perennial stem under the soil surface.  The bulb portion is small and has very thin papery leaves on its surface.  Corms function as a storage of food and reproductive organ.

Cortex - Underneath the epidermis layer is the cortex tissue.  This area is a mass of irregular shaped parenchyma cells with many intercellular spaces. The cortex tissues are largely a storage place for water and nutrients.

Coulter Injection - Use of a narrow coulter and high pressure to place a fluid fertilizer in a vertical band from the soil surface to the depth of coulter penetration.  A variation of banded fertilizer application.

Critical deficiency limit - The lowest level of tissue nutrient content from which you can expect adequate growth.  Below this, deficiencies are likely.

Critical toxicity limit - The highest level of tissue nutrient content from which you can expect adequate growth.  Above this limit, toxicities are likely.

Crop Nutrient Budget - A balance sheet showing the nutrient applied to the crop and the nutrients removed by the crop. Only a portion of the nutrients needed by a crop is removed from the field at harvest.  Grain crops remove less nutrients per unit of harvest than forage crops.

Crop Nutrient Recycling - Returning to the soil the nutrients contained in plant residues.

Crop Nutrient Removal - Nutrients removed in harvested crops. Perhaps the most critical factor when evaluating the sustainability of a farming system.  Simply put, if the nutrients removed from a field are not replaced, the system is not sustainable.  When nutrients removed in harvested crops are not returned, the result is a decline in soil productivity.
The two nutrients most susceptible to depletion through crop removal are phosphorus (P) and potassium (K).  Unlike nitrogen (N), which can be partially replenished by rotation with legume crops, there is no biological method of replacing P and K.  Once soil supplies are depleted through crop removal, the only method of replacement is through importation of outside sources.  The source can be organic residues, manures, or commercial fertilizers.

Crop Nutrient Sources - Plants obtain essential nutrients from a number of sources including soil minerals, organic matter, commercial fertilizers, legumes (N), animal wastes, sewage sludge, and other wastes. Plants do not distinguish between these sources.  All nutrients are taken up in identical inorganic forms regardless of source.

Crop Nutrient Uptake - Large quantities of nutrients are contained in the above ground portion of crops.  Total nutrient demand is often referred to as crop nutrient uptake.

Crop Residue Management (CRM) - A year-round system beginning with the selection of crops that produce sufficient quantities of residue and may include limited secondary harvest of residue.  CRM includes all field operations that affect residue amounts, orientation and distribution throughout the period requiring protection.  Site-specific residue cover amounts needed are usually expressed in percentage but may also be in pounds.

Cross Section of Herbaceous Stems - Since herbaceous stems are mostly of primary growth tissues, its cross section is very much like the cross section of a growing root.  It has an epidermis, cortex, stele with phloem and xylem tissues.  There is often considerable pith in the stems of these annual plants.

Cross Section of Root - A vertical or cross section of a root shows a structure which is composed of epidermis, cortex, endodermis, pericycle, xylem, phloem and parenchyma tissues.  In time, the older portions of the roots develop cambium tissues.

Cross Section of Woody Stems - ross section of woody stemmed plants shows both primary and secondary tissue.

Cytoplasm - l of the living substances in a cell outside of the nucleus is called the cytoplasm.  It is not uniform in its appearance and contains many types of structure, such as cytoplasmic membranes and plastids.

Cytoplasmic Membrane - The cytoplasmic membrane surrounds the cytoplasm and exists just inside the cell wall.  It controls the entry and exit of materials into and from the cytoplasm.

Damping-Off - Sudden wilting and death of seedling plants resulting from attack by microorganisms.

DeciSiemen per meter (dS/m) - The preferred unit to express electrical conductivity.  One dS/m  = one mS/cm = one mmhos/cm = (p.m./700).

Deep Banding Fertilization - Deep banding refers to preplant applications of nutrients placed 2 to 6 inches below the soil surface. Some applications are deeper, as much as 15 inches.  The applied nutrients may be in solid, fluid, or gaseous forms. Concentrated zones of nutrients are produced, either streams sheets or points, depending on the design of the applicator.  In some areas this fertilization technique is performed many months before the next crop is seeded, often in conjunction with a tillage operation.  Reduced tillage grain drills have been adapted for one-pass seeding and deep placement of fertilizer either between and rows or below the seed. Other common terms for deep banding include "deep placement," "dual placement," "dual banding," "knifing," "preplant banding," "double shooting," "triple shooting," "root zone banding," and "tillage implement application."  Dual application implies simultaneous application of anhydrous ammonia as the main nitrogen source and either fluid or solid phosphorus, potassium, and sulfur fertilizers.  Otherwise, deep banding terminology can imply the use of either fluid or solid fertilizers.  See Also: Banded Fertilizer; Coulter Injection; Double Shooting; Dual Placement; Knifed application; Triple Shooting .

Deficiency - When the concentration of a nutrient becomes low enough in a plant to cause decreased growth or tissue damage.  It is often accompanied by visual symptoms.

Deionization - A water purification process for removing ions (cations and anions) from water using ion exchange resins.

Denitrification - The process by which nitrates or nitrites in the soil or organic deposits are reduced to lower oxides of nitrogen by bacterial action.  The process results in the escape of nitrogen into the air.

Differentiation Zones - The older meristematic cells of a young root change to mature tissues. They develop xylem, phloem and other tissues to carry absorbed nutrients up into the stems, etc., and return synthesized material to the growing sections of the root.

Diffused Roots - When a primary root branches quickly into many slender roots it develops a diffused or fibrous root system.  There may be several main roots which are about equal in diameter and have many branching root systems.  When the length of all of the roots and rootlets are added together, a mature well-developed plant such as a native prairie grass plant, may have a root length of thousands of miles.

Diffusion - Diffusion is the equalization of the concentration of nutrients solutions which exists between the root cells and soil solution.  The stronger salt solutions move from the soil to the less concentrated solutions inside the cells.  This movement takes place easily and rapidly when the root membranes, root hairs, are permeable to the soil solutions and its solutes.

Digestion - The process, which converts water insoluble food into water soluble foods, or changes complex food into simpler foods for utilization, is called digestion.  It usually proceeds transportation, assimilation and respiration.  Also, it requires an enzyme to aid in this process.  Chemically, it is known as hydrolysis.

Distillation - A water purification process where water is heated into vapor form (which leaves impurities behind) and is then condensed to produce purified water.

Dolomite - A lime composed of calcium-magnesium carbonate [CaMg(CO₃)₂].  Pure dolomite contains 13.1% Mg.  Dolomite is often used interchangeably and incorrectly for dolomitic lime. A material used for liming soils in areas were magnesium and calcium are needed.  Made by grinding dolomitic limestone, which contains both magnesium carbonate, MgCO₃, and calcium carbonate, CaCO₃.  (See also Lime). A lime composed primarily of calcium carbonate (calcite, CaCO₃), with a lesser content of calcium-magnesium carbonate [dolomite, CaMg(CO₃)₂].  Any lime that contains some Mg from dolomite is called dolomitic lime, but the concentration of Mg varies greatly, from 1.3 to 11.7%.

Double Shooting - Synonymous with dual placement or dual application. Placement of two fertilizer materials in subsurface bands using separate delivery tubes.
See also: Dual Placement.

Dribble Fertilization - Dribbling or strip banding is a form of band placement that involves application of solid or fluid fertilizers in bands or strips of varying widths on the soil surface or on the surface of crop residues. Zones of high nutrient concentration are produced which improve nutrient use efficiency.  Typically, the fertilizer material contacts 25% to 30 % of the soil surface.  If these surface strip applications are followed by tillage, the concentration effect is diluted to something between broadcast application and deep banding where the concentrated zones remain intact.
See also: Broadcast Application; Deep Banding Fertilization .

Drip Irrigation - See Low-Volume Irrigation

Drip irrigation system - An irrigation system where water is delivered to the soil/growing media surface below the plant canopy, usually by small nozzles, emitters, or tubes.

DTPA - Diethylenetriaminepentaacetic acid.  A chelating agent that is used to chelate ferric (Fe⁺³) iron.  DTPA is used on acid to slightly alkaline soils and in many chelated liquid fertilizer formulations.

Dual Placement of Application - Placement of two fertilizer materials in subsurface bands.  Application: Usually accomplished through injection of the two materials from two tubes at two points on an applicator shank. For example, anhydrous ammonia and fluid ammonium polyphosphate (10-34-0) or a mixed liquid fertilizer containing other nutrients many be dual applied. See Also: Deep Banding Fertilization; Double Shooting.

Ebb-and-flow flooded floor system - An ebb-and-flow subirrigation system that uses molded concrete floors as the flood container.

Ebb-and-flow subirrigation system - A subirrigation growing system where containerized plants are placed in watertight trays or molded concrete floors that are flooded when needed with nutrient solution, then drained.  Usually the nutrient solution is collected and recirculated.  Also called ebb & flow, ebb-and-flood, flood irrigation, and pulsed subirrigation.

Ebb-and-flow tray system - An ebb-and-flow subirrigation system that uses watertight trays, usually placed on benches, as the flood container.

ECe - Electrical conductivity of a saturated soil extract.

Ecology - The branch of biology that deals with the mutual relations among organisms and between organisms and their environment.

Ecw - Electrical conductivity of water.

EDDHA - Ethylenediaminetetraacetic-o-hydroxyphenylacetic acid, a chelating agent used to chelate ferric iron (Fe⁺³ ); used on highly alkaline soils/media.  Very expensive.

EDTA - Ethylenediaminetetraacetic acid, a chelating agent used to chelate ferric iron (Fe⁺³ ), manganese, copper, and zinc.  Used on slightly acid soils/media and in many chelated liquid fertilizer formulations and hydroponic nutrient solutions.

Electrical conductivity (EC) - The ability of a solution to conduct electricity due to dissolved or  suspended ionic solutes.  Used as a measure of soluble salt content of water.  Preferred to be expressed as deciSiemen/meter (ds/m), but often expressed as milliSiemen/centimeter (mS/cm), millimhos/centimeter (mmhos/cm), EC ´ 10-3, or micromhos/centimeter (µmhos/cm).  Each dissolved salt has its own unique conductivity, hence, EC is only an approximation of the actual salt content of a solution [ppm = (ds/m)(700)].

Electrodialysis - A water purification process where water is passed over electrically charge membranes to remove ionic solutes.

Electrolytes - Any compound or material that forms ions when dissolved in water, thus forming a conductor of electricity, such as all soluble salts.

Element (chemical) - Basic chemical substance consisting of chemically uniform atoms; there are  92 natural elements arranged in the periodic system.

Elemental sulfur - The elemental form of sulfur used to decrease soil pH (increase acidity) in alkaline soil/growing media.

Elongation Region - As new cells develop, they elongate and push the meristematic section and root cap ahead.  With this elongation, more protoplasm and vacuoles accumulate to nourish and stimulate the meristematic region.  This active growing region is not more than a few millimeters in length.

Emulsion - Heterogeneous mixture of liquids (e.g., fat droplets in water).

Environment - All external conditions that may act upon an organism or soil to influence its development, including sunlight, temperature, moisture and other organisms.

Enzymes
Protein substances produced by living cells which modify the rate of chemical reactions.  They are organic catalysts.

Epidermis of the Leaves - The tissue which forms a covering layer over leaves, the softer portions of stems and roots, etc., is called epidermal tissue.  Its thickness is usually one cell.  On the stems and leaves it often has a waxy substance, cutin, on its outside walls.  The function of this epidermis is largely for protection to prevent excessive evaporation of water and aid the root in its absorption of substances from the soil.   On leaves and some stems, this epidermal tissue contains openings or pores called stomata, where gases are exchanged.

Epidermis of the Roots - The outer or surface layer of the root tissues is the epidermis.  In the young root, its function is largely that of protection and absorption of water and nutrients.  As the roots become larger and older, this layer may be sloughed off and replaced by a layer of cork.

Epidermis - The epidermal tissues are the single layers of cells on the upper and lower surfaces of a leaf.  The ordinary epidermal cells are tightly packed and colorless.  They serve as a protection of the inner tissues from mechanical injury, parasite invasions and from dehydration.

Epsom salt - Magnesium sulfate (MgSO₄.7H₂O); used primarily as a magnesium fertilizer, but it also supplies sulfur.  Used to supply Mg without altering soil/growing media pH.

Eq.- Amount of substance, numerically equal in grams to equivalent weight, e.g.,
for KCl (potassium chloride): 1 eq.= 74.6 g (Univalent cation),
for MgSO₄ (magnesium sulfate):   1 eq.= 60 g(bivalent cation),
See also mole, equivalent weight, valence .

Equilibrium reaction (pHc) - A mathematical measure similar to pH, but it also takes into account the alkalinity, calcium, magnesium, carbonate, and bicarbonate  content of water.

Equivalent - A mole (Avogadro's number) of charges (positive or negative).  One mole of a  monovalent cation would contain one equivalent of positive charges, whereas one mole of a divalent cation would contain two equivalents of positive charges.

Equivalent weight - Molecular weight of substance, divided by valence (see eq .).

Erect Stems - When the shoots grow upright, such as corn, cotton, alfalfa, shrub and tree plants, they are called plants with erect stems.  Most of the branching shoots of such plants have a tendency to grow upright.

Erosion - The wearing away of the land surface by detachment and transport of soil and rock materials through the action of moving water, wind or other geological agents.

Essential element - One of the 17 elements that plants need for normal growth and development and to complete their life cycle.  They are: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), boron (B), molybdenum (Mo), chlorine (CI), and potentially nickel (Ni).

ESP - see Exchangeable Sodium Percentage

Eutrophication - A condition in stagnant pools and lakes usually characterized by an abundant accumulation of nutrients that supports a dense growth of plant and animal life, the decay of which depletes the shallow waters of oxygen in summer.

Evapotranspiration (ET) - The sum of water evaporation and transpiration. The loss of water from a soil by evaporation and plant transpiration.

Exchangeable Base - A basic cation (Ca⁺², Mg⁺², K⁺, NH₄⁺) adsorbed on a soil colloid, but which can be replaced by hydrogen (H+) or some other cation.
See Also: Cation Exchange .

Exchangeable Ions - Ions held on the soil complex that may be replaced by other ions of like charge.  Ions which are held so tightly that they cannot be exchanged are called nonexchangeable.

Exchangeable Sodium Percentage - The degree of saturation of the soil exchange complex with sodium.  It may be calculated by the formula:
ESP = Exchangeable sodium (me/100 g soil)/Cation exchange capacity (me/100 g soil) * 100

Exchangeable Sodium Percentage (ESP)
The degree of saturation of the soil exchange complex with sodium (Na).
May be calculated by the following formula: Soil cation exchange capacity (CEC) = 12 milliequivalents (meq)/100 grams
 Calcium (Ca⁺²) = 7 meq/100 grams
 Potassium (K⁺) = 2 meq/100 grams
 Magnesium (Mg⁺²) = 2 meq/100 grams
 Sodium (Na⁺) = 1 meq/100 grams
ESP = 1 meq Na/12 meq/100 soil x 100 = 8.33%
Reducing exchangeable Na to 5% of the soil's CEC (cation exchange capacity) is a target of many reclamation plans.

Expressed sap tissue testing - The use of analytical techniques to determine the nutrient content of plant sap.

Fallow - Cropland left idle in order to restore productivity, mainly through accumulation of water, nutrients or both.  Summer fallow is a common stage before cereal grain in regions of limited rainfall.  The soil is tilled for at least one growing season to control weeds, to aid decomposition of plant residues and to encourage the storage of moisture for the succeeding grain crop.  Bush or forest fallow is a rest period under woody vegetation between crops. The practice of allowing cropland to be left idle in order to enhance productivity, mainly through accumulation of water, release of nutrients from organic matter, or both.
Summer fallow is a common practice in cereal grain production systems in regions of limited rainfall.  The soil is kept weed-free for one growing season by tillage or herbicides in order to store moisture and nutrients for the following grain crop.  However, moisture storage is relatively inefficient.

Ferric - The form of iron in the +3 valency form (Fe⁺³ ).  Ferric iron is the insoluble form found in most soils.

Ferrous - The form of iron in the +2 valency form (Fe⁺²).  Ferrous iron is the primary form of iron plants absorb.

Fertigation - A term often used to describe the application of soluble fertilizers in the irrigation water.  Also called liquid feed. : Application of fertilizer in irrigation water. Nitrogen is the most common plant nutrient applied in irrigation water. Both sprinkler and furrow irrigation systems can be utilized.  Anhydrous ammonia, urea-ammonium nitrate (UAN) solutions and solid nitrogen sources such as urea have been effectively applied in this manner.  Care has to be given to the injection of anhydrous ammonia into water containing large amounts of dissolved carbonates and bicarbonates to avoid precipitation of salts within the irrigation system.  Ammonia application through a sprinkler irrigation system can lead to substantial volatilization losses.  Sulfur can also be easily applied in this manner.  Common sulfur sources for fertigation would include ammonium thiosulfate, ammonium sulfate, ammonium polysulfide and potassium thiosulfate.
See Also: Chemigation .

Fertilizer - Any natural or manufactured material added to the soil in order to supply one or more plant nutrients.  The term is generally applied to manufactured materials other than lime or gypsum. AAPFCO officialis: "Any substance containing one or more recognized plant nutrient(s) which is used for its plant nutrient content and which is designed for use or claimed to have value in promoting plant growth, except unmanipulated animal and vegetable manures, marl, lime, limestone, wood ashes, and other products exempted by regulation." Fertilizer is food for plants.  It contains nutrients needed to supplement the soil's supply, which is often less than that required to satisfy demands for optimum crop production. The most common fertilizer nutrients are nitrogen (N), phosphorus (P), and potassium (K).  These three nutrients are needed in largest amounts by crops and are most often the ones first limiting in soils.  The composition of fertilizer varies depending on the crop for which it will be used and the nutrient status of the soil.

Fertilizer analysis - A sequence of three numbers on all fertilizer labels that gives the percent composition, on a weight basis, of N-P2O5-K2O in the fertilizer.

Fertilizer Application - Various methods of delivery of chemical fertilizer to the soil.

Fertilizer Formula - The quantity and grade of materials used in making a fertilizer mixture.

Fertilizer Grade - An expression that indicates the weight percentage of plant nutrients in a fertilizer.  Thus a 10-20-10 grade contains 10 percent nitrogen (N), 20 percent phosphoric acid (P₂O₅) and 10 percent potash (K₂ O).

Fertilizer injector - A device attached to the irrigation line to inject a small amount of concentrated fertilizer into the water stream to yield a dilute concentration of  fertilizer in the irrigation water.  The injector ratio or proportion varies from1:15 (i.e., dilutes 1 part fertilizer concentrate to every 15 parts of irrigation water) to 1:400.  On some injectors the proportion can be varied.

Fertilizer Placement - Concentration fertilizer into a band or strip at a specific location on or below the soil surface.  Examples: starter, dribble fertilization, deep banding.

Fertilizer ratio - The fertilizer analysis reduced to the least common denominator, which yields the ratio of N-P₂O₅-K₂ O.  For example, a 18-6-12 analysis has a 3-1-2 ratio.

Fertilizer Soil Reaction Zone - That volume of soil containing fertilizer components and/or their reaction products before they are dispersed by soil water or tillage.  The size of the fertilizer-soil reaction zone is determined by fertilizer physical form (solid or fluid), rate of application, particle size, and method of application as well as soil physical and chemical properties.

Fertilizer Use Efficiency - An expression of the units of yield per unit of nutrient provided for the crop.  Common expressions include bushels of grain per pound of applied nutrient or pounds of yield per pounds of applied nutrient.
Any production practice which improves the final crop yield directly affects fertilizer use efficiency.  When a superior variety or hybrid increases grain yields by 5%, for example, this translates directly to a similar increase in fertilizer use efficiency.  Rotation, planting date, seeding rate, and method of fertilizer application can have similar effects.

Field Moisture Capacity - The moisture content of soil in the field two or three days after a thorough wetting of the soil profile by rain or irrigation water.  Field capacity is expressed as moisture percentage, dry-weight basis.

Fifteen-Atmosphere Percentage - The moisture percentage, dry-weight basis, of a soil sample which has been wetted and brought to equilibrium in a pressure-membrane apparatus at a pressure of 221 psi.  This characteristic moisture value for soils approximates the lower limit of water available for plant growth.  (See also Permanent Wilting Percentage.)

Fixation - Processes by which available plant nutrients are rendered unavailable by reaction with soil components.  Generally, refers to reactions of phosphorus, ammonium, and potassium leading to decreased availability. The more acid the soil and the higher its clay content, the greater its capacity to fix phosphorus.  On such soils, liming and applying the phosphate in bands to lessen its contact with the soil have been the conventional remedies to lessen fixation and improve nutrient use efficiency. Soils differ in their capacity to fix potassium, depending on the kinds and amounts of clay minerals they contain.  Fixed potassium ions are trapped between the silica sheets of certain soil clay minerals, including especially vermiculite and illite.  These trapped ions may be slowly released over time.
Ammonium ions from ammonia-based fertilizers, legumes, and wastes also can be fixed by the same clay minerals that fix potassium, and in the same manner. (See also Reversion and Nitrogen Fixation .)

Flocculation - The aggregation of particles into larger masses.  Flocculation is used in water treatment to aggregate contaminants, which are then precipitated.

Flooded floor - See ebb-and-flow flooded floor system .

Floriculture - Production of foliage or flowering ornamental plants in fields or greenhouses for commercial sales.

Flotation Applicator - A type of fertilizer applicator equipped with large, low pressure tires intended to spread the weight of the vehicle over a large soil surface area.

Flow Divider - Mechanical device used for splitting a stream of liquid fertilizer to achieve uniform distribution to individual application points.

Flower Parts - When these flowering parts develop into a perfect or complete flower, there are four kinds of floral organs: sepals, petals, stamens and pistil.

Flowers - The flower part of seed plants is a highly modified shoot which develops into reproductive organisms.  The development of a bud into a flowering shoot depends on many factors such as heredity, photoperiods, moisture, food supply, temperature, etc.

Fog system - A device that dispenses fine droplets of water that stay suspended in the air.  Used for temperature and humidity control in greenhouses and propagation.

Foliar analysis - Nutrient analysis of leaf tissue.

Foliar Diagnosis - Estimation of the nutrient status of a plant or the nutrient requirements of the soil for producing a crop through chemical analysis or color manifestations of plant leaves, or by both methods.

Foliar Fertilization - Supplying plant nutrients through leaves, with absorption taking place through the stomata of leaves and leaf cuticles.

Foliar Fertilization - Application of soluble fertilizers in the form of spray to the foliage of plants.

Forage - Unharvested plant material which can be used as feed by domestic animals.  Forage may be grazed or cut for hay or silage.

Frit - A slow-release fertilizer with the nutrients impregnated into powdered glass.  Frit is most commonly used for potassium or iron.

Fruit - A fruit is a mature ovary of a flower such as an apple, tomato, etc.  There are many kinds of fruits.

Function of Leaves - The important function of most leaves is the manufacture of food for photosynthesis.  Associated with photosynthesis are other physiological processes in leaves such as transpiration, respiration, digestion and assimilation.  All of these chemical transformations involve the physiological and functional processes which take place in living cells are called metabolism.

Function of Plant Roots - There are four important functions of plant roots; namely, absorption of plant foods, transportation of foods to and from stems, storage of foods, and anchorage.

Function of Stems - The chief function of stems is to conduct materials and produce support for leaves and reproduction organs.  Raw materials or nutrients absorbed from the soil solution are transported from the roots to the leaves by the stem tissues. After these plant food materials are manufactured into plant materials in the leaves, these synthesized materials are transported by the stems to the growing regions of the plant, to the roots, to the storage tissues. The bud or growing part of a stem produces more stem tissues for the leaves, which manufacture plant materials.  Also stems provide support for the reproductive organs or flowers.
 The stems of some plants provide storage for absorbed nutrients and synthesized plant materials.  Often, these stored materials are used for new growth later in the season or next year.

Geographic Information Systems (GIS) - Technology that links satellite positioning data to on-board map information for variable rate applications, variable rate planting and yield mapping.

Global Positioning Systems (GPS) - The term global positioning system (GPS) refers to a network of U.S. Defense Department satellites that provide exact location coordinates to computers on board tractors, fertilizer applicators, trucks, combines and other vehicles.
The GPS system is an integral part of variable rate fertilization systems that allows site-specific fertilizer application and permits the applicator operator with an on-board computer to know precisely the equipment's location within the field at all times.  The GPS system is also utilized with variable-rate planting equipment and field-mapping harvesting equipment. A cursor on the on-board computer screen relates the equipment location to a field map.  The applicator operator is then able to change rates of application while traveling across the field to adapt to soil test information stored in the on-board computer.  The equipment does not have to be operated in straight lines.  A trail line on the screen lets the operator know where the applicator has been. GPS also benefits application on the increasing number of fields farmed on the contour or terrace.

Grade - The guaranteed analysis of a fertilizer containing one or more of the primary plant nutrient elements.  Grades are stated in terms of the guaranteed percentages of nitrogen (N), available phosphate (P₂O₅) and potash (K₂O), in that order.  For example, a 10-10-10 grade would contain 10 percent nitrogen, 10 percent available phosphate, and 10 percent potash.
 (See also Analysis ).

Gray Water - See Recycled Water .

Green Manure - Crops grown especially to be plowed under for the benefit of succeeding crops.
Common green manures are alfalfa, clovers, buckwheat, cowpeas, small grains, and other crops.

Growing media - The substrate in which plant's roots grow.  Usually it is a highly amended or totally soilless mixture made from organic and inorganic components.  Also called potting soil, soilless media, mix, or substrate.

Ground Cover - Plants grown for their low, spreading habit, to protect soils, to prevent the growth of weeds and for aesthetic purposes.

Guano - The decomposed dried excrement of birds and bats, used for fertilizer purposes.  The most commonly know guano comes from islands off the coast of Peru and is derived from the excrement of seafowl.  It is high in nitrogen and phosphate and at one time was a major fertilizer in this country.

Guarantees - The AAPFCO official regulation follows: The statement of guarantees of mixed fertilizer shall be given in whole numbers.  All fertilizer components with the exception of potash (K₂O) and phosphoric acid (P₂O₅ ), if guaranteed, shall be stated in terms of the elements.

Gypsum - Calcium sulfate .  Gypsum is used primarily as a calcium fertilizer, and it also supplies sulfur.  Most often used as a calcium fertilizer when you do not alter soil/growing media pH.

Gypsum (CaSO₄.2H₂O) - The common name for calcium sulfate, a mineral used in the fertilizer industry as a source of calcium and sulfur.  Gypsum also is used widely in reclaiming alkali soils in the western United States.  Gypsum cannot be used as a liming material, but it may reduce the alkalinity of sodic soils by replacing sodium with calcium.  Another common name is landplaster.  When pure it contains approximately 18.6 percent sulfur.

Half-life - The length of time for one-half of a compound to disappear or be used.

Hardpan - A hardened or cemented soil horizon or layer.  The soil material may be sandy or clayey and may be cemented by iron oxide, silica, calcium carbonate or other substances. A hardened or cemented soil horizon or layer.  The soil material may be sandy or clayey and may be cemented by iron oxide, silica, calcium carbonate, or other substances.

Hard water - A water high in calcium and/or magnesium.

HEDTA - hydroxyethylethylenediaminetriacetic acid, a chelating agent used to chelate ferric iron (Fe³⁺ ).  HEDTA is used under moderately alkaline soil conditions.  Also abbreviated HEEDTA.

Herbaceous Stems - Herbaceous stems are soft and green.  They consist largely of primary tissues which develop annually.  They are usually slender or narrow in diameter with an outer covering of epidermal tissue.

Heterotrophic Bacteria - A category of soil bacteria that obtain their energy and carbon directly from soil organic matter.  Most soil bacteria fit in this category. The general-purpose decay and ammonifying bacteria are heterotrophic.  Fungi and actinomycetes are also heterotrophic in character.
See Also: Actinomycetes .

High Pressure Injection - A stream or pulse of fluid fertilizer forced below the soil surface at 2000 to 6000 psi without prior opening of the soil by some mechanical means.  Pressures for this type of application are many times higher than those used in coulter injection.

Hoagland Solution - Nutrient solution containing all essential plant nutrients, and used for hydroponically grown plants.  Original nutrient solution was developed by Professor Hoagland at the University of California.

Hollow-fiber membranes - A type of membrane used in water purification systems.

Horizon Soil - A layer of soil, approximately parallel to the soil surface, with distinct characteristics produced by soil-forming processes.

Horticulture - The science of producing and using ornamental plants, fruits and vegetables.

Humification - The process of forming humus, well decomposed organic matter, in soils. Humification in soils is controlled mainly by factors which are favorable for microbial activity.  Among these are optimum soil moisture, temperature and aeration, as well as a source of energy.  Incorporation of crop residues and appropriate tillage also promote soil organic matter formation.  Humification is needed to maintain soil organic matter levels since decomposition of soil humus occurs during much of the year.  Loss of soil organic matter leads to low water holding capacity, soil compaction, increased erosion, and decreased productive capacity.

Humus - Dark brown or black substances consisting of well decomposed organic matter that provides nutrients for plants and increases the water retention of soil.  Humus constitutes from one fifth to one half of the organic matter in peat, compost, leaf mold, and rotted animal manures. The importance of humus to the growth of crops is due principally to its high buffer capacity over a considerable range of pH values.  It tends to stabilize soil structure and has a high cation exchange capacity. The well-decomposed, more or less stable portion of the organic matter in mineral soils.

Hydrated lime - Lime composed of calcium hydroxide [Ca(OH)₂ ].  Hydrated lime is used to raise media pH quickly.

Hydrogen Ion Concentration - See pH .

Hydrolysis - Reaction of a salt with ions of water, e.g., CaCO₃ + 2(H⁺ + OH^-)  » Ca(OH)₂ + H₂CO₃ .

Hydroponics - Cultivation of plants by placing the roots in liquid nutrient solutions rather than in soil/growing media.  The soilless culture or water culture of plants. The production of plants in a liquid solution or gravel medium supplemented with all required nutrients for proper growth. The production of plants in a liquid solution or gravel medium supplemented with all required nutrients for proper growth. AAPFCO official is " . . . a system in which water-soluble nutrients are placed in intimate contact with the plant's root system, being grown in an inert supportive medium which supplies physical support for the roots but which does not add or subtract plant nutrients."

Hydroxide - Compound containing (OH^- )-ions; hydroxides of metals are also called bases.

Hygroscopic - Capable of taking up moisture from the air.

Immobile - A term used to describe translocation of a nutrient in plants when the nutrient only travels up the stem and into organs via the xylem, but it cannot be loaded into the phloem to travel out of organs or down stems.  Deficiencies of immobile nutrients always occur on the young leaves first.

Impregnation - Thorough mixing or spraying of a small amount of herbicide, fungicide, or other pesticide in a large amount of fertilizer. Normally done through bulk blending operations.  Onboard impregnation during application is growing in importance.

Inclusions - Also inside a plant cell are solid inclusions and solutions which may be either waste products or synthesized foods for the living protoplasm and vacuoles.  These inclusions may include starch grains, oil drops, protein bodies, and salt crystals.

Incorporation - Mechanical mixing of fertilizer materials with the surface soil.

Injection - Placement of fluid fertilizer or anhydrous ammonia in the soil either through use of pressure or nonpressure systems.
See Also: Deep Banding Fertilization; Double Shooting; Dual Placement; Knifed Application; Point Injection; Spoke Injection .

Inorganic - A compound or substance that is not carbon based.  When used to describe fertilizers, it includes the mineral forms, such as potassium nitrate, superphosphate, etc.  When used to describe growing media components, it includes mineral, synthetic, or non- biological forms, such as perlite, vermiculite, sand, etc. Substances occurring as minerals in nature or obtainable from them by chemical means.  Refers to all matter except the compounds of carbon, but includes carbonates.

Insoluble - Not soluble.  As applied to phosphoric acid in fertilizer, that portion of the total phosphoric acid which is soluble neither in water nor in neutral ammonium citrate.  As applied to potash and nitrogen, not soluble in water.

Integrated pest management (IPM) - The use of multiple approaches to control pest damage, including variety selection, economic considerations,  cultural control, sanitation, timing of planting, biological control, pesticides, etc.

Internal Structure of Leaves - Under a microscope, a cross section of a leaf shows three types of tissues: epidermis, mesophyll and veins.

Interveinal - Between the veins of the leaves.

Ion - An electrically charged particle.  As used in soils, an ion refers to an electrically charged element or combination of elements resulting from the breakage up of an electrolyte in solution.  Since most soil solutions are very dilute, many of the salts exist as ions.  For example, all or part of the potassium chloride (muriate of potash) in most soils exists as potassium ions and chloride ions.  The positively charged potassium ion is a cation, and the negatively charged chloride ion is an anion. Any atom or molecule that is electrically charged due to loss of electrons, which results in a positively charged cation; or the gain of electrons, which results in a negatively charged anion.

Ion exchange resin - A solid matrix or beads containing fixed positive and/or negative charges that remove ions from water by ion exchange.

Iron (Fe) - Iron (Fe) is an essential metallic micronutrient and is absorbed by plants as the ferrous (Fe⁺²) ion. Iron is a catalyst in chlorophyll formation and acts as an oxygen carrier.  It also helps form certain respiratory enzyme systems in the plant.  The nutrient is immobile in plants.  Iron deficiency shows up as a very light pale leaf color with veins remaining green, usually first appearing on younger leaves; but severe deficiency may result in the entire plant showing such symptoms.  Iron deficiency may be caused by an imbalance with other metals such as molybdenum (Mo), copper (Cu), or manganese (Mn).  Other factors contributing to iron deficiency include high availability of soil P, high soil pH, wet and cold soil conditions, low soil organic matter, and plant genetic differences.  Deficiencies of this element can be determined by soil analysis.

Kelp - Any of several species of seaweed sometimes harvested for use as a fertilizer.  Dried kelp will usually contain 1.6 to 3.3 percent N, 1 to 2 percent P₂O₅ and 15 to 20 percent K₂O.

Knifed Application - Process where fertilizer materials are banded into the soil with a slender knifing tool.
See Also: Deep Banding Fertilization; Double Shooting; Dual Placement; Injection.

Leaching - Removal of nutrients, salts, pesticides, or other water soluble compounds from growing media with water.  Irrigation and rain leaches compounds from soil/growing media, and propagation mist leaches compounds from cuttings. The removal of materials in solution by the passage of water through soil.  In agriculture, leaching refers to the downward movement of free water (percolation) out of the plant root zone.  It occurs when the amount of rainfall or irrigation water entering the soil becomes greater than its water holding capacity.  Most likely to occur on coarse textured soils.
Leaching of nutrients, particularly nitrate-nitrogen (NO₃^- ), can cause decreased nutrient use efficiency, lower yields, and environmental problems including nitrate accumulation in groundwater.  Best management practices minimize this type of nutrient loss, usually through multiple nutrient applications close to the time of nutrient need and through the use of nitrification inhibitors.  In some cases, leaching is intentionally practiced to remove accumulations of soluble salts from soils.

Leaching potential - A measure of a pesticide's tendency to move in solution with water and leach below the root zone into deep percolation in the soil.

Leaching requirement (LR) - The fraction of water applied during each irrigation that passes through the root zone and out the bottom of the container or soil profile.  An LR of 0.5 means 50% of the irrigation water would pass through the container or soil profile.  You can estimate the LR needed to maintain a certain soil salinity level by LR =Ecw/[5/(ECe-ECw)]; where ECw is the electrical conductivity of the irrigation water and ECe is the electrical conductivity of a saturated soil extract.

Leaching Requirement - The fraction of the water entering the soil that must pass through the root zone in order to prevent soil salinity from exceeding a specified value.  Leaching requirement is used primarily under steady-state or long-time average conditions.

Leaf Blades - Leaf blades are usually flat and thin to permit good penetration of light and CO2.  They vary in shape, size, venation, margins, etc., for the different plants.

Leaf Margins - There are three types of leaf margins; entire, toothed and lobed.  The entire margins are the smooth and unindented blade edges.  The toothed margins are indented as saw teeth.  These indentations may be small, large and variously shaped.  Lobed margins have the large indentation of irregular shape.  These indentations vary with the plant species.

Leaf Size - Leaves may vary in length from a fraction of an inch to over fifty feet.  Their width may range from a fraction of an inch to over 24 inches.

Leaf Shape - In shape, leaf blades vary from long narrow blades, such as grass blades, to round or circular forms. There are many variations between these extremes in shape.

Leaves - Leaves are the lateral outgrowth of buds which arise at nodes in the stems.  They develop from meristematic tissues as lateral protuberances of the bud tip.  These protuberances enlarge into leaves when they grow.  Most leaves are flat, however there are various modifications and specialized kinds of leaves.  Food manufacture is the important function of most leaves.  One or several leaves may develop at a node.  They can have several arrangements, such as alternate, opposite, spiral or whirled.  They may last for only one growing season (deciduous) or several seasons (evergreen).

Legumes - Plants of the family Leguminosae characterized botanically by fruit called a legume or pod that opens along two sutures when ripe.  Some samples of legumes are alfalfa, soybeans, peas, clovers, and vetches.
Legumes in symbiotic relationship with Rhizobium bacteria fix atmosphere nitrogen in the nodules on the plant's roots.  It has been estimated that from 100 to 300 pounds of nitrogen per acre may be fixed annually be a leguminous crops.

Leucoplast - The colorless food-producing plastids are called leucoplasts.  They collect sugars and transform them into starches.  They are abundant in roots, tubers and similar storage organs.

Lignosulfonate - A mixture of sulfonated lignins derived as byproducts of the pulp/paper process. Used as a chelating agent for iron, manganese, copper, and zinc.

Lime - Technically, calcium oxide (CaO).  Practically or agriculturally, it is any material containing the carbonates, oxides, and/or hydroxides of calcium and/or magnesium used to neutralize soil/media acidity.  The most common ones used are calcitic lime, dolomitic lime, dolomite, and hydrated lime.  Also called limestone.

Lime - Generally the term lime, or agricultural lime, is applied to ground limestone (calcium carbonate), hydrated lime (calcium hydroxide) or burned lime (calcium oxide), with or without mixtures ofmagnesium carbonate, magnesium hydroxide or magnesium oxide, and to materials such as basic slag, used a amendments to reduce the acidity of acid soils.  In strict chemical terminology, lime refers to calcium oxide (CaO), but by an extension of meaning it is now used for all limestone-derived materials applied to neutralize acid soils.

Lime Requirement -The amount of standard ground limestone required to bring a 6.6-inch layer of an acre (about 2 million pounds in mineral soils) of acid soil to some specific lesser degree of acidity, usually to slightly or very slightly acid.  In common practice, lime requirements are given in tons per acre of nearly pure limestone, ground finely enough so that all of it passes a 10-mesh screen and at least half of it passes a 100-mesh screen. Lime requirement is the amount of good quality agricultural limestone required to establish the desired soil pH range for the cropping system being used.  Lime requirements are determined in the laboratory using a buffer pH in equilibrium with the soil.  Lime requirement is NOT determined by the soil pH alone but is primarily by the soil's cation exchange capacity.  The specific requirement is usually expressed in terms of effective calcium carbonate equivalent (ECCE) which is based on the calcium carbonate equivalent content of the liming agent and its fineness of grind.  Smaller particles react faster in the soil.  Different liming materials have different neutralizing values depending upon their chemical composition.

Limestone - See lime .

Liquid Fertilizer -A fluid in which the plant nutrients are in true solution.

LISA - Acronym for Low Input Sustainable Agriculture.
Farming systems that economize on the use of manufactured inputs, notably fertilizers and pesticides, but also chemicals used to prevent livestock diseases or promote growth.  The emphasis is on minimizing the use of agricultural chemicals without drastically reducing crop yields or livestock production.

Loam - The textural class name for soil having a moderate amount of sand, silt, and clay.  Loam soils contain 7% to 27% clay, 28% to 50% silt, and less than 52% sand.
See Also: Soil Texture .

Loam - The textural class name for soil having a moderate amount of sand, silt and clay.  Loam soils contain 7 to 27 percent clay, 28 to 50 percent silt, and less than 52 percent sand.  (In the old literature, especially English literature, the term loam applied to mellow soils rich in organic matter, regardless of the texture.  As used in the United States, the term refers only to the relative amounts of sand, silt and clay; loam soils may or may not be mellow.)

Longitudinal Section - As a root develops and elongates it develops four regions of cells, the root cap, meristematic region, elongation region and maturation region.

Low-Volume Irrigation -Irrigation system including drip, micro sprinklers, misters or foggers, or any system that is designed to apply water in or near the rooting zone in relatively precise amounts with respect to the plants needs.

Luxury Consumption-The uptake by a plant of an essential nutrient in amounts exceeding what is needs.  Thus if potassium is abundant in the soil, alfalfa may take in more than is required. A phenomenon brought about by the availability to plants of nutrients from any source which causes uptake of nutrients beyond those amounts required for normal growth and function.
The normal physiological function of plants may be upset by excessive accumulation of some nutrients, e.g., excessive nitrogen (N) may prolong the vegetative cycle and delay maturing or it may even prevent flowering, excessive phosphorus (P) may decrease plant uptake of zinc (Zn) and other micronutrients, and excessive potassium (K) may decrease plant uptake of magnesium (Mg).

Macronutrients - Nutrients that plants require in relatively large amounts; nitrogen (N), phosphorus (P), and potassium (K).
Magnesium is a constituent of chlorophyll and is actively involved in photosynthesis.  Much of the magnesium in plants is found in the chlorophyll.  Seeds are also relatively high in magnesium, though grain crops such as corn have low magnesium levels in the seed.  Magnesium aids in phosphate metabolism, plant utilization of sugars, and the activation of several enzyme systems.  Magnesium is mobile in the plant and deficiency symptoms first appear on the lower (older) leaves.  It appears first as a light, yellowish, faded discoloration with the veins remaining green.  In crops such as corn, the leaves are yellowish or very light green striped while veins remain green.  In some crops, as the deficiency progresses, a reddish-purple color develops with green veins.  Deficiencies can be determined by soil and plant analysis.

Macronutrient - One of the six essential elements required by plants in larger quantities (0.2 to 7%).  They are: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca),  magnesium (Mg), and sulfur (S).

Magnesium (Mg) - Magnesium (Mg) is an essential secondary nutrient classed with calcium and sulfur.  It exists in the soils and is absorbed by the plant as the Mg⁺² ion.  Its oxidation state in the plant does not change. Magnesium is a constituent of chlorophyll and is actively involved in photosynthesis.  Much of the magnesium in plants is found in the chlorophyll.  Seeds are also relatively high in magnesium, though grain crops such as corn have low magnesium levels in the seed.  Magnesium aids in phosphate metabolism, plant utilization of sugars, and the activation of several enzyme systems.  Magnesium is mobile in the plant and deficiency symptoms first appear on the lower (older) leaves.  It appears first as a light, yellowish, faded discoloration with the veins remaining green.  In crops such as corn, the leaves are yellowish or very light green striped while veins remain green.  In some crops, as the deficiency progresses, a reddish-purple color develops with green veins.  Deficiencies can be determined by soil and plant analysis.

Major element - See macronutrient .

Manganese (Mn) - Manganese (Mn) is a metallic micronutrient existing in the soil in several oxidation states of which the Mn⁺² ion is the form most commonly absorbed by plants. Manganese functions pri