A-B-C-D-E-F-G-H-I-J-K-L-M-N-O-P-Q-R-S-T-U-V-W-X-Y-Z 

-A- 

Acid or Acidity:  An acid is the chemical opposite of a base.  As developed by Bronsted & Lowry, a substance that tends to give up protons (hydrogen ions) to some other substance.  The earlier theory of Arrhenius described an acid as any substance yielding protons (hydrogen ions) when dissolved in water.

Acid Injection:  The process by which acid is injected into water or soil to treat waters with high Bicarbonate and Carbonate content.  Adding an acid evolves the Bicarbonate and Carbonate off as Carbon Dioxide and water.

Alkali:  A soluble mineral salt or a mixture of soluble salts, present in some soils, especially in arid regions, and detrimental to the growing of most crops.  Alkali is often used as a synonym for “sodic,” referring to high levels of sodium (relative to Calcium and Magnesium) in water or soil.

Alkalinity:  A measure of the buffering capacity of water to neutralize acids.  The presence of buffering materials helps neutralize acids as they are added to the water. These buffering materials are primarily Bicarbonate, and Carbonate, and occasionally Hydroxide, Borates, Silicates, Phosphates, Ammonium, Sulfides, and Organic Ligands.

-B-

Base:  A base is the chemical opposite of an acid.  A base in chemistry is a chemical substance, which has a free pair of electrons to bind a Hydrogen ion (H) commonly referred to as a proton.  Another common definition of a base is a chemical compound that absorbs hydronium ions (H₃O) when dissolved in water (a proton acceptor) because protons do not generally occur in a free state.

  
Base Saturation:  An important property of soils, which generally reflects the extent of leaching and weathering of the soil.  It is defined as the percentage of Total Cation Exchange Capacity (CEC) occupied by such common basic cations as Calcium, Magnesium, Sodium and Potassium.  As a general rule, the degree of base saturation or normal uncultivated soils is higher for arid than for humid region soils. The concept of base saturation is important in agriculture because the relative proportion of acids and bases on the exchange sites determines a soil's pH.  As the number of Calcium and Magnesium ions decreases and the number of Hydrogen and Aluminum ions increases, the pH drops.  Adding limestone replaces acidic Hydrogen and Aluminum cations with basic Calcium and Magnesium cations, which increases the base saturation and raises the pH.

Bicarbonate:  (HCO₃) equivalent weight = 61.  A salt of carbonic acid, containing the HCO₃-1 group.  Bicarbonate often combines with Calcium and Magnesium to form Calcium Carbonate and Magnesium Carbonate, which are forms of insoluble Lime and Calcite.  Bicarbonates are one of the components in water that define its alkalinity.

Buffering Capacity:  Buffering capacity refers to water's ability to keep its pH stable as acids or bases are added.  The pH and buffering capacity of water are intertwined with one another.  If water has sufficient buffering capacity it can absorb and neutralize added acid without significantly changing its pH.  In soils, buffering capacity is the ability to withstand rapid pH fluctuation.  The greater the buffering capacity, the greater the quantity of acid or base which must be incorporated with a material to alter the soil’s pH.  Generally speaking, in arid soils the higher the Calcium Carbonate level the greater its buffering capacity.

  
-C- 

Calcium:  (Ca) equivalent weight = 20.  A silvery, moderately hard metallic element that constitutes approximately three percent of the earth's crust and is a basic component of most animals and plants.  It is an essential plant nutrient and the cation responsible for good soil structure.

Calcium Carbonate:  (CaCO₃) A chemical compound that is the active ingredient in agricultural lime.  It is an insoluble form of Calcium precipitated by waters high in Calcium, Bicarbonate, and Carbonate.  Calcium Carbonate sometimes occurs naturally in calcareous/ caliche soils in arid regions, and is insoluble until broken up by an acid.  Calcium Carbonate is one of the components in water that defines its alkalinity.

Calcium/Magnesium Carbonate:  (CaCO₃·MgCO₃ Dolomitic Lime).  An insoluble Calcium/ Magnesium combination precipitated from waters high in Calcium, Magnesium, Bicarbonate and Carbonate.  Calcium/Magnesium Carbonate sometimes occurs naturally in calcareous/ caliche soils in arid regions and is insoluble until broken up by an acid.  It is produced as an insoluble Calcium/Magnesium combination precipitated from waters high in Calcium, Magnesium, Bicarbonate and Carbonate.

Calcareous Soil:  A soil type that is formed from or contains a high proportion of Calcium Carbonate in the form of Calcite or Aragonite.  It also contains sufficient free Calcium Carbonate such that it effervesces visibly or audibly when treated with cold 0.1m hydrochloric acid.  They are often very fertile, but can be flinty, thin, and dry.  These soils often form a large part of the soil of deserts, which may prove very fertile when sufficient moisture for crops is applied.

Calcite: (CaCO₃)  A Calcium Carbonate that is one of the most widely distributed minerals on the Earth's surface.  It is a common constituent of sedimentary rocks; limestone in particular.  It is also a Lime precipitant from a water source.

  
Calcium Nitrate: (CaNO₃)  A highly soluble source of Calcium and Nitrogen that can be dissolved in irrigation water to lower the Sodium Absorption Rate (SAR) or increase the Electrical Conductivity of Water (EC_W).  It is extremely hygroscopic, thus making it useable in only dry climates.

Calcium Sulfate: (CaSO₄)  A chemical commonly referred to as ‘Gypsum’.  Calcium Sulfate is an amendment used to displace sodium at the soil exchange site and allow for increased soil permeability.  It can also be suspended in irrigation water to increase Electrical Conductivity of Water (EC_w) or the ratio of Calcium/Sodium, thereby lowering Sodium Absorption Rate (SAR).  It is used often as an agricultural amendment or fertilizer to displace exchangeable sodium to allow increase soil permeability.

Cation Exchange Capacity:  (CEC)  In soils, it is a reversible process in which cations (Calcium, Magnesium, Potassium and Sodium) are held on the solid phase (or soil colloids) and exchanged with another kind of cation in the liquid phase (or soil solution).  Compared to anion exchange, the cation exchange is generally considered to be more important, because the anion and molecular retention capacity of most agricultural soils is much smaller than the cation retention capacity.  The relative ability of soils to store one particular group of nutrients, the cations, in preference to anions is referred to as cation exchange capacity or CEC.  Therefore, the total number of cations a soil can hold--or its total negative charge--is the soil's cation exchange capacity.  The higher the CEC is, the higher the negative charge; thus, the more cations that can be held.  Therefore, soils with a high CEC will tend to hold on to nutrients better than soils with a low CEC.

Carbonate: (CO₃) equivalent weight = 30.  A salt of Carbonic Acid.  A Carbonate in the soil often combines with Calcium to form Calcium Carbonate  or Magnesium to form Magnesium Carbonate.

-D- 

Decisiemens per Meter:  (dS m-1)  The standard measurement used to report electrical conductivity of water (EC_w).

-E- 

Eaton’s Gypsum Requirement: (EGR) a component in measuring the Sodium Hazard Potential of water.

Electrical Conductivity:  (EC_e)  A measure of a material’s ability to conduct between electrodes placed in a sample of the water; the value obtained relates to the nature and amount of salts present in the water and increases with concentration.  The EC_e of soil can be measured from a saturated paste extract with distilled water by measuring the electrical resistance of the soil: water suspension.

Electrical Conductivity of Irrigation Water:  (EC_W)  This is a measurement of the total salinity or total dissolved salts (TDS).  640 ppm TDS = 1.0 dS/m EC_w.  EC does not give specific information about the chemical species present in water, but it can be used as an acceptable indicator for water quality as an approximate determination of TDS.

Electrolytes:  Substances that conduct electricity by the movement of ions.  All compounds that dissolve in water with the formation of ions are called electrolytes.

Evapotranspiration:  The rate of water loss through transpiration from vegetation plus evaporation from the soil surface or from standing water on the soil surface - mm/day or m3/day.

Exchangeable Sodium Percentage:  (ESP)  Measurement used to classify sodic and saline-sodic conditions.  ESP is calculated as a proportion of the cation exchange capacity (CEC) occupied by the sodium ions and is expressed as a percentage in relationship to Calcium, Magnesium, Potassium and Sodium as a whole.  ESP has been used to classify sodic and saline-sodic conditions as the degree of sodium saturation of the soil exchange complex (as measured by the CEC) as compared to other exchangeable cations.

-F- 

Field Capacity:  The moisture content of soil in the field after rapid drainage has ceased, usually 2 to 3 days after a thorough wetting of the soil profile.  Field capacity is expressed as moisture percentage on a volume weight basis.  It is often assumed to be approximately represented by soil in equilibrium with 1/3 bar (or atmospheres) pressure equivalent to 330 cm of water suction or a water potential of -33 kpa (S1 units).

-G- 

Gypsum:  (CaSO₄·2H₂O) A very soft mineral composed of Calcium Sulfate Dihydrate. It’s an ameliorant for sodium-affected (sodic) soils that occur mainly in arid areas.  It’s also a source of the nutrients Calcium and Sulfur required for crops.  It is an ameliorant for the subsoil acidity syndrome that commonly afflicts soils in the Southeast U.S.A. and it’s an ameliorant for crust and seal formation at the soil surface, a condition commonly encountered in sandy textured soils.  It can be used as an ameliorant for sodium-affected soils that occur mainly in arid areas; but especially where the soil’s Calcium content is reduced.  It’s also an excellent source of the nutrients Calcium and Sulfur, which are required by most crops.

-H- 

Hardness or Hard Water:  Originally, water hardness was understood to be a measure of the capacity of water to precipitate soap.  The harder the water the more soap is required.  Soap is precipitated primarily by the Calcium and Magnesium ions present in the water.  However and as science has evolved, it has been determined that the principal cations causing hardness in water are Calcium, Magnesium, Strontium, Iron and Manganese.  Major anions associated with the principal cations are Bicarbonates, Sulfates, Chlorides, Nitrates and Silicates.  By mathematical calculation, the preferred method for determining water hardness is to compute it from the results of separate determinations of Calcium and Magnesium.  Thus, Total Hardness = Calcium Hardness + Magnesium Hardness.  To the extent that water contains Bicarbonate ions in conjunction with the ions of Calcium and Magnesium and Iron, the water may display Carbonate hardness (or temporary hardness).  When the alkalinity of water is less than its Total Hardness, then Carbonate Hardness is present.  When the alkalinity is greater than or equal to the Total Hardness, then Noncarbonate hardness is present.

-I- 

Ion Exchange:  The process in water of replacement of one ion by another.  In soils, it is a reversible process by which one type of cation or anion held on the solid phase is exchanged with another kind of cation or anion in the liquid phase.

-L- 

Leach:  To dissolve out soluble constituents such as salts from the soil profile by percolation.  Good drainage is critical so that as salts are leached down, they drain out and away from the root zone so that water uptake is not hampered.

Lime:  A soil amendment used to change or raise the soil’s pH.  Dolomitic Limestone (Calcium Carbonate and Magnesium Carbonate) adds Calcium and Magnesium in addition to increasing the pH.  If soil pH is reduced too low due to over acidification, the addition of Lime will increase the soils buffering capacity.  Technically speaking, lime refers to Calcium Oxide (CaO), but the term has universally included Calcium Carbonate, Calcium-Magnesium Carbonate, and Calcium Silicate slags.

Liming:  An agricultural term that refers to the addition to the soil of any Calcium and Magnesium-containing compound that is capable of reducing acidity.

-M- 

Magnesium:  (Mg) equivalent weight = 12.  A chemical element that is essential to all living cells.  Magnesium is an important plant nutrient and cation associated with good soil structure, providing it is not available in excessive quantities in relationship to Calcium.

Magnesium Carbonate:  (MgCO₃)  A white solid that occurs in nature as a mineral.  It is insoluble and is a form of Magnesium precipitated by waters high in Magnesium, Bicarbonate, and Carbonate.  Magnesium Carbonate often occurs naturally in calcareous/ caliche infiltration and soil aeration.

Millequivalents per Liter:  (meq/l)  A form of measurement that is equal to parts per million (ppm) divided by equivalent weight.

Milligrams per Liter:  (mg L-1)  Equals parts per million.  A form of measurement.

-P- 

pH:  A measure of the acidity of a solution, in terms of activity of Hydrogen ions (H+). Aqueous solutions with pH values lower than 7 are considered acidic, while values higher than 7 are considered basic.  On the pH scale, a shift up in value by one number represents a ten-fold decrease in value.  For example, a shift in pH from 2 to 3 represents a decrease in total concentration of Hydrogen concentration by a factor of 10, and a shift from 2 to 4 represents a one-hundred fold decrease (10 X 10) in Hydrogen concentration.

Parts per Million:  (ppm)  Millequivalents per liter multiplied by equivalent weight. Potassium:  (K) Atomic Weight = 39.  A chemical element that is essential to all living cells.  The proper level of Potassium is essential for normal cell function.

-R- 

Residual Sodium Carbonate:  (RSC)  A measurement that compares the concentrations of Calcium and Magnesium to Bicarbonate and Carbonate, and determines when Calcium and Magnesium precipitation can occur in the soil and result in additional sodium domination of soil cation exchange sites.  The RSC equals the sum of the Bicarbonate and Carbonate ion concentrations minus the sum of the Calcium and Magnesium ion concentrations, where the ions are expressed in mEq/L.

Root Zone:  The area of the soil around the plant that supports the roots.  The root zone is the conduit for plants to obtain the essential micronutrients needed for growth and development. For the root zone to effectively channel nutrients to the plant it must be periodically leached of excess levels of salts that may interfere with proper root uptake.

-S- 

Salinity:  The amount of soluble salts in water.  Salinity in water is measured as electrical conductivity for soluble salts (“EC), total dissolved solids (“TDS”), or total soluble salts (“TSS”).  Much, but not all saline water is also sodic in nature.  Such water is usually relatively high in Carbonates and Bicarbonates (alkalinity) as well.  Generally speaking, saline water with high pH (> 8.5) has a tendency to have high sodium associated with it.  Saline water with low pHs (pH < 8.5) typically do not have high sodium concentrations.

Salt-Affected Soils:  Soils defined as saline, saline-alkali and sodic.  In general, salt-affected soils usually have low biological activity because of osmotic and ionic effects of salts due to limitations of carbonaceous substrates.  In effect, a salt-affected soil is a soil that has been adversely affected to the extent that it is no longer suitable for the growth of most crops due to the presence or action of soluble salts.

Salts:  Any ionic compound composed of cations (positively charged ions) and anions (negative ions) so that the product is neutral (without a net charge).  Salts include: Chlorides of Calcium, Magnesium and Potassium, and Bicarbonates and Sulfates of Sodium, Calcium, Magnesium and Potassium.  Anything that is soluble in water is considered a salt.

Saline Soil:  A saline soil is a soil that contains a quantity of soluble salts sufficient to interfere with the growth of most crops.  A saline soil is also a non-sodic soil.  In the USDA definition, the EC >4 mmhos/cm, pH <8.5 and ESP<15%.

  
Salinization:  The process by which a nonsaline soil becomes saline, as by the irrigation of land with brackish water.  Natural salinization may occur by such means as seawater intrusion and sea-spray drift.  All other salinization is “human-induced salinization” or “secondary salinization.”  Its causes include irrigation with saline waters and interventions that have the effect of raising the water table. More specifically, it is the process by which a nonsaline soil becomes saline, as by the irrigation of land with brackish water.

Saline/Sodic Soil:  A saline/sodic soil is a non-sodic soil containing soluble salts in such quantities that interfere with the growth of most plants.  In the USDA definition, the EC>4 mmhos/cm, pH<8.5, and ESP >15%.  Any soil that is high in both salinity and sodicity.

SO₂ Generator: (commonly referred to as a Sulfur Burner). Equipment used to reduce or eliminate carbonates and/or bicarbonates from irrigation water.  SO₂ Generators burn sulfur which produces sulfurous gas that, when combined with water, becomes sulfuric acid.  The sulfuric acid is then diluted to lower the pH level of the treated solution to the desired level.  The process evolves the Bicarbonate and Carbonate off as Carbon Dioxide and water.  This is another method of acid injection; however, it is a much safer means of delivering the acid since it is created on-site and on-demand instead of stored in volume.

Sodic Soil:  A soil that has sodicity as its predominant characteristic, with EC <4 mmhos/cm, pH ≥8.5, and ESP≥15%.  It is also the same as Non-Saline Sodic Soil and Alkali Soil.

Sodification:  The process whereby the exchangeable sodium content of soil is increased, often by cumulative irrigation with sodic or brackish water.  In general, sodification tends to occur naturally; whereas salinization tends to occur as a result of poor irrigation management.

Sodicity:  A term used to describe the condition of a sodic (alkali) soil, the sodicity hazard or sodicity problem of the soil.  The amount of Sodium in water in relation to the amounts of Calcium and Magnesium as measured by the water’s SAR.  It may also be measured in relation to the amounts of Calcium, Magnesium, Bicarbonates and Carbonates in the water as measured by adjusted Sodium Absorption Rate (SARa).

Sodicity Hazard:  The amount of sodicity in the water such that it adversely affects agricultural yield or the health and appearance of crops or turf.  The higher the sodicity, the greater the potential for developing a sodicity hazard.  A secondary method of classifying sodicity hazard is Residual Sodium Carbonate, which measures the dominance of Sodium and Carbonate over Calcium and Magnesium in water.

Sodium:  (Na)  Sodium is present as salt (Sodium Chloride, NaCl) in huge quantities in underground deposits (salt mines) and seawater and other natural waters.  It is easily recovered as a solid by drying.

Sodium Absorption Ratio of Irrigation Water: (SAR_W)  A measurement used to determine whether Sodium levels of water will cause soil structure to deteriorate.  Unadjusted SAR (SAR_W) considers only Sodium, Calcium, and Magnesium, while adjusted SAR (adj. SAR_W) also includes the influence of Bicarbonate and Carbonate on Sodium activity.

Sodium Sulfate:  (Na₂SO₄)  A soluble salt formed when Gypsum is used to treat soils with high Sodium content.

Softness or Water Softening or Soft Water:  Water that has the ions of Calcium, Magnesium and Iron removed or in low concentrations.  The softer the water the lesser the amount of soap required.  Water that contains the ions of Calcium, Magnesium and Iron but lesser Bicarbonate ions is referred to as Noncarbonate Hardness (or Permanent Hardness).

Soil Profile:  Generally speaking and in terms of agronomic applications, the soil profile is that portion of a soil that contains the roots of a crop. It is commonly referred to as the “rooting depth.”  Soil formation begins first with the break down of rock into regolith.  Continued weathering and soil horizon development process leads to the development of a soil profile, the vertical display of soil horizons.

Sulfate:  (SO₄) equivalent weight = 48.  A chemical compound containing the bivalent group SO₄.  When combined with Lime, while in an acid form, Calcium Sulfate is formed which may later be transformed into the dihydrate of Calcium Sulfate or Gypsum.  Note that in excess concentrations in water, Sulfate contributes to sealing and scum buildup and thus may collect on the walls of vessels or pipes that continually hold hot water.

Sulfur:  (S)  A secondary plant nutrient used as a soil amendment to modify pH in alkaline soils.  Sulfur is often used in calcareous and caliche soils (containing high lime) to assist in breaking down Lime into Gypsum.

Sulfuric Acid:  (H₂SO₄)  A strong mineral acid.  It is soluble in water at all concentrations.  Sulfuric Acid forms in soil when acidifying amendments/ fertilizers are used such as soil Sulfur, Ammonium Sulfate, etc., or is injected into irrigation water via a sulfurous generator or acid injection which uses products such as Urea Sulfuric Acid (NpHURIC).

Sulfurous Acid:  (H₂SO₃)  A name given to aqueous solutions of sulfur dioxide.  Because sulfurous acid is short-lived, there is no evidence of its existence in aqueous solutions. Sulfurous Acid is an unstable compound that seeks out dissolved oxygen to stabilize itself as Sulfuric Acid.

-T- 

Total Dissolved Salts:  (TDS)  Amount of dissolved salts present in a solution, normally reported as parts per million (ppm).

Total Soluble Salts:  Generally speaking, it is a measure of the amount of salinity in a solution of the solution-soluble ions.  It is also used to reference water-soluble salts. Therefore, it has been generally acceptable to consider Total Dissolved Salts (TDS) as a surrogate measure of those salts in solution as Total Soluble Salts (TSS).  However, the use of the term TSS has also been used in the agricultural industry to indicate a measure of the soluble salts of water plus the soluble salts of an applied fertilizer through the water, thus making the TSS content of the solution being applied to an agricultural soil.

Transpiration:   The passage of water through a plant from the roots through the vascular system to the atmosphere – usually through the leaves.  Anything that inhibits a plant’s ability to take up water via transpiration (approximately 75 cm. of water) will reduce its ability to grow and develop.  Plants transpire pure water, leaving salts behind in the soil.

-W- 

Water:  The universal solvent which has properties related to its Hydrogen and Oxygen content and its ability to solubilize Carbon Dioxide and produce alkaline conditions.  In modern chemistry, the term “alkaline” is preferable to “basic” because the term “basic” has other connotations and meanings.