Glossary mat_mws 7 avril 2015



This glossary is a work tool, and any constructive proposals for a better understanding of the terms will be welcomed. This glossary is not presented in alphabetical order: it is to read as is, prior to reading any document on liming. Underlined terms used in the definitions are defined in the glossary. In some cases, remarks are added to the definition to make a clarification for the reader. Finally, we found it necessary to quote a number of terms that should not be used because of the confusion that their use generates.
“Source COMIFER”






Notions on the ground

noun. Chemical entity (molecule, ion, …) liable to give H + (proton) to another chemical entity that is a base.
adj. : Refers to a chemical entity likely to give H + (proton) to another chemical entity which is then called a base. Also used for a solution or a soil whose effective acidity or salt replaceable acidity is considered high.
Note: This quality is subjective, use with caution.
Action of adding an acid.
Change resulting from the addition of acid or acid-producing reactions (or consuming bases).
This action or these changes may lead to more or less long term lowering of the pH.
Effective acidityor Active acidity:
Concentration of H3O+ (denoted H+ for abbreviation) in the soil solution.
Note: This concentration depends on what is referred to as “ground solution”. It depends on the exchange soil acidity but also the dilution ratio (or soil water content) and the composition of the solution. The measurement method of this magnitude must always be specified. (See pH).
Salt Replaceable Acidity:
Amount of H + and Al3 + derived by processing a given mass of a soil sample by a neutral unbuffered salt.
Note: This amount depends on the neutral salt used.
Titratable acidity until a given pH:
Acidity evaluated by the amount of base consumed when the pH of a soil sample is brought from from its current value to a given value.
Note: The titratable acidity depends on the pH (initial and final) of the provided base and the cation associated with the solution (suspension in water, KCl, …), the contact time …
Retention of a molecule, an ion …, on the surface of the body by various physical or chemical process (electrostatic attraction, complexation, Van der Waals bonds, …).
See Basic
Action of adding a base.
Changes resulting from the provision of a base or reactions consuming protons.
Alkalinity or Acid Neutralising Capacity, ANC:
Amount of base that can be neutralized with a strong acid, (expressed in cmol (OH) per kg of soil).
Basic Lime Amendment or Liming Material:
Fertilizer material characterized by a high basicity anion (O2-, HO, CO32-, silicate anions and calcium phosphates) and a cation of negligible acidity (Ca2+, Mg2+ mainly).
Note: The main advantage of a basic amendment is to neutralize all or part of the acidity of a soil.
Basiccalcium and / or magnesium amendment:
Basic Amendment containing CaO, Ca (OH)2, CaCO3, with the presence of their magnesium counterparts.
Chemical entity having both acidic and basic properties.
Negatively charged ion (eg NO3).


Chemical entity (molecule, ion, …) capable of accepting one or several H+ (proton) from another chemical entity which is an acid.
Note: In practice, the provision of a base neutralizes the H+ and thus reduces soil acidity.
Adj. : Refers to a chemical entity possessing the properties of a base, or with a pH> 7.
Need for Base (BEB) :
Basic amendment amount needed to neutralize some of the acidity of a given amount of land.
Note: BEB VN is expressed in units (in kg CaO / ha). The part of acidity to neutralize can be estimated in many ways.
Proton Balance H+ Balance:
Difference between protons or products made and consumed or lost in an ecosystem.


Cation exchange capacity (CEC):
Amount of cationic charge retained by the negative charge of an adsorbent system and capable of being exchanged in a reversible manner.
This quantity is estimated by a chemical or conventional physicochemical measure performed on a soil sample.
Note: Conditions (pH, type and concentration of cations and anions, …) greatly affect the result; it is necessary to indicate the method used. See Adsorption, effective CEC, CEC “Metson” exchangeable cations, cmol + kg-1 soil, permanent load, variable load, load pH dependent.
Effective cation exchange capacity (CECE):
CEC evaluated by a method that barely modifies the ground, in particular the pH and ion concentration of the solution.
Note: The three main methods use chlorides hexaammine cobalt or “Cohex”, barium and potassium salts.
Note: This method is not usable for the calculation of the need for bases.
Cation :
Positively charged ion (eg Ca++, K+).
Exchangeable Cations:
Cations held by the adsorption complex that compensate the negative charge, and whose burden can be replaced by other cations from the soil solution.
Note: See Electrical Neutrality, Adsorption. The analysis method affects the results: in the presence of CaCO3 method “Metson” overestimates the content of exchangeable calcium.
Effective CEC or “CEC at soil pH”:
See Effective Cation Exchange Capacity.
CEC “Metson” :
CEC evaluated by the “Metson” method, characterized inter alia by a measurement buffered to a pH close to 7.
Note: In general, the CEC Metson overestimates the effective CEC for acid soils and underestimates for basic soils. See Load pH dependent.
pH Dependent load:
Variable load whose value depends on the pH.
See variable or proton load.
Structural Charge:
Charge, almost always negative, of certain minerals (phyllosilicates and mainly manganates phyllo) due to substitution in the crystal lattice of certain cations by other cations of a different charge (“isomorphic substitution”). Note: In the case of a negative permanent charge, the replacing cation has an electrical charge smaller than the original cation.
Proton charge:
Load due to the dissociation or association of protons (H +) with surface functional groups of the solid phase of the soil, organic or inorganic. This charge depends on the pH and composition of the solution. Note: It is always negative for humus, but it can be positive or negative for oxides (iron, aluminum …).
Cultivation technique consisting of providing a basic amendment to the soil. Note: This term covers both basic amendments raw and cooked.
cmol :
symbol for centimole (hundredth of a mole). See mol.
cmol(+) :
symbol for centimole of positive charge. Example: 1 cmol (+) is the charge carried by ½ cmol of Ca2 + or K + 1 cmol. ou cmol+/kg :
Symbol for centimole of positive charge per kilogram (fine earth). Expression unit of the CEC and exchangeable cations. Note: The result is numerically equal to the expression in milliequivalents per 100 grams of clay (meq / 100g or meq / 100g).


Decarbonatation :
Decrease in carbonate content of the soil due to acidification. Note: The term decalcarification is to be avoided.
Decalcification :
Loss of calcium from the soil by leaching or by export crops. In non-calcareous soils it is mainly due to their replacement by protons (H+) on the adsorbent system. This is a consequence of acidification.
Charge density:
Electrical charge, surface or mass, soil constituents (see CEC).
Reverse process of adsorption.


Acid strength:
Qualitative indication of the ability of an acid to H+. Note: The acidity is said to be “strong”, “weak”, “negligible”. See Ka.
Base strength:
Qualitative indication of the ability of a base to accept H +. Note: … so to give birth to Hoen aqueous solution. The alkalinity will be called “strong”, “weak”, “negligible”. See Kb.


Ka Acidity Constant:
Quantitative assessment of the strength of an acid in water. Ka = ([H3O+] [A].) / [HA], HA and A form an acid / base pair conjugates.
Kb Alkalinity Constant:
Quantitative assessment of the strength of a base in water. = 10-14 Kb / Ka, Ka is the acidity constant of the conjugate acid (see Ka).


Mechanical drive of solid particles in the ground by gravity-fed water. Often wrongly used to designate leaching.
Drive of elements dissolved by gravity-fed water.


meq :
Milli equivalent see cmol
mol :
Symbol of the mole: mole contains 6,022* 1,023 elementary molecules.
mol.l-1 or mol / l :
Symbol of moles per liter.


Acid-base neutrality:
Characteristic of an aqueous solution wherein the concentrations of H3O + and HO are equal, ie, the pH is equal to 7 at 25 ° C. By extension: A characteristic of a chemical entity whose aqueous solution meets the above criteria.
Electrical neutrality:
State of matter in equilibrium resulting in equality between the positive charges and the negative charges.


pH :
Potential Hydrogen Abbreviation. Figure indicated, related to the concentration of H3O + from an aqueous solution (denoted H+ for short).
In dilute solution, pH = log10 [H+] (or [H+] = 10 pH) with [H+] expressed in mol/l
Soil pH:
pH of a soil sample suspended in pure water or in solutions (KCl, CaCl2) in a given ratio.
Note: The values of pHwater and pH 0.01M CaCl2 are different, and both are different from that of the soil solution.
pHwater :
pH of a soil suspended in pure water in an earth / given water ratio (1/5 by volume in the French standard).
pHKCI 1M :
pH of soil suspended in a potassium chloride solution of molar concentration. The pH can also be measured with other salts in given concentrations. Example pH CaCl2 0.01M.
pKa :
Equal to -log Ka. When the pH equals the pKa, the concentration of an acid and its conjugate base are equal. The higher the pKa, the more the acid is weak.
Buffer capacity:
Property conferred to the ground by some chemical entities (in the solid state, dissolved or adsorbed), to moderate a change in concentration of H+, potassium, phosphorus, … in the soil solution after contributions, productions, levies or loss of H+, potassium, phosphorus …
Particle constituent of the atomic nucleus. Nucleus of the hydrogen atom; it carries a positive elementary charge. Chemical symbol H+.


S :
See sum of exchangeable cations of negligible acidity.
Soil solution:
Liquid phase of the soil.
Sum of exchangeable cations (denoted S):
Sum of exchangeable cations negligible acidity. It essentially corresponds to the sum of the charges carried by Ca2+, Mg2+, K+, Na+.
Note: cations and S are in cmol+ .kg-1 or cmol+ / kg.
Sorption :
Removal of an ion or molecule of the soil solution and retention of the substance (the sorbate) at the surface (adsorption) and inside (absorption in the narrow sense) another substance (the sorbent) . This term is often used when the exact mechanism is not known.
Notes :
(1) The forces that hold the sorbent can be chemically predominant (chemisorption) or physical, including capillary forces (the process can be called capillary condensation);
(2) a subsequent loss of sorbed by the sorbent is called desorption;
(3) in common language, absorption is in use in the most general sense to enter or leave a liquid or a gas in its own substance.


T :
See Cation Exchange Capacity. Note: previously used in the formula for saturation, this term should be abandoned. One must indicate the method used for determining the CEC(Metson, cobaltihexamine, effective, Mehlich, …).
Rate of Acidity Exchange:
Percentage of the actual CEC occupied by acidic exchangeable cations (H+ and Al3+), all expressed in cmol+ / kg: TAE = 100 (M+ + Al3+) / (Ca2+ + Mg2+ + K + Na+ + H+ + Al3+
Taux de saturation
(S / CEC or S / T or V) Saturation rate:
Percentage of CEC occupied by exchangeable cations of negligible acidity: S / CEC% = 100 x (Ca2+ + Mg2++ + K + Na +) / CEC. Note: You must specify the S and CEC determination method. The cations, S and CEC are in cmol + kg-1 or cmol + / kg.


Mass indicator often used to quantify the nutrients.
This term is quantitatively equivalent to the kilogram. However, we prefer to use the units for the nutrients and kilograms for products made.
Example: a contribution of 100 kg of KCl grading 60 K2O corresponds to a contribution of 60 units of K2O.


V :
See saturation rate of the CEC.
Note: Do not use this term.
Neutralizing value:
The neutralizing value (VN) of a product, in particular a basic amendment, is expressed by the mass (kg) of calcium oxide (CaO) that has the same neutralizing ability as 100kg of the product. It is measured by the action of a strong acid (HCl). An amendment grading 54% CaO has a neutralizing value of 54.
Note: The neutralizing value is a conventional chemical measurement that expresses the potential ability of a basic amendment to neutralize the acidity of soil. The expression of this potential depends on environmental conditions, and in certain cases, of the finesse and hardness of amendment particles.




Symbols and Abbreviations


 mol :
symbol of the mole: mole contains 6.023 * 1,023 elementary entities.
mol.L-1 :
symbol of moles per liter.
 cmol :
symbol of centimole (hundredth of moles).
cmol+ :
symbol of centimole positive charge.
example: 1 + cmol is the load carried by 1/2 cmol Ca2+ or K+ 1 cmol. :
centimole symbol of positive charge per kilogram (fine earth). Expression unit of the CEC, exchangeable cations.
Note: the result is numerically equal to the old term in milliequivalents per 100 grams of soil (mis / 100g or meq / 100g).
S :
sum of exchangeable cations of negligible acidity: Ca2+, Mg2+, K+, Na+ .See saturation rate.
T :
 see Capacity of cation exchange.
V :
see rate of saturation.
Active Acidity:
for simplicity, use the term effective acidity.
Reserve acidity, potential acidity:
these two terms are confusing. They will be, as appropriate, usefully replaced by titratable acidity, exchangeable acidity, buffer capacity vis-à-vis the pH.




Terms to avoid

Liming, Lime Amendment:
prefer the following terms: basic calcium amendment/ fertilizer (quicklime, slaked lime, limestone) or calcium neutral amendment (calcium sulfate or gypsum, calcium chloride, calcium nitrate).
Exchangeable Bases:
misnomer for exchangeable cations of negligible acidity: cation can not accept H+ (the basic definition), it repels it. In the hydrated state, some cations have significant acidic properties (Fe3+, Al3+), others have a negligible acidity (Na+, K+, Mg2+, Ca2+).
Basic Cation:
misnomer for Ca2+, Mg2+, K+, Na essentially, they have a negligible acidity in solutions(see exchangeable bases)
Soil pH:
strictly speaking, the measure addresses a soil sample.