Thesoil cation interchange capacity ( CEC)is the ability of soils to stick and store a particular group of nutrients by electric attractiveness , those that form positively charged cations , such as calcium ( Ca2 + ) , magnesium ( Mg2 + ) , potassium ( K+ ) , and nitrogen in the mannikin of ammonium ( NH4 + ) .
Soils are composed of a mixture of grit , silt , stiff and organic topic . The particles ofclayandorganic matterin ground post an electrical charge , they have anet disconfirming charge(- ) . This allows them to attract and holdpositively - charged particles(+ ) , because ‘ opposites pull in ’ , much like how opposite poles of a magnet attract each other . They also repulse other negatively - charged particles ( - ) , because ‘ like repels like ’ , much like how similar poles of a magnet repel each other .
filth with a low CEC are not able to bind much nutrient mote to their particles , while those with a high-pitched CEC are able-bodied to bind a larger amount of nutrient speck to the surface of the soil particles .
What Are Anions and Cations?
chemic elements ( such as atomic number 20 , magnesium , iron ) do n’t normally have an electrical bang , but when they fall back or gain electrons , they then win an electric charge , and are calledions .
A great mnemonic to remember which is which , is to substitute the missive ‘ t ‘ with a ‘ + ‘ symbolisation in the wordca+ions .
Somecommon filth cations(with their chemic symbol and charge ) include calcium ( Ca2 + ) , Mg ( Mg2 + ) , atomic number 19 ( K+ ) , ammonium ( NH4 + ) , hydrogen ( H+ ) and sodium ( Na+ )
Somecommon soil anions(with their chemic symbolisation and charge ) include chlorine ( Cl- ) , nitrate ( NO3- ) , sulfate ( S042- ) and phosphate ( PO43- )
Note : from the list above , we can see that some cations have more than one ( + ) incontrovertible bursting charge , while some anions can have more than one ( - ) damaging charge and also be conflate with atomic number 8 .
How Soil Cation Exchange Capacity Works
The cations that are bound to the particles of corpse and organic matter in soils can be replaced by other types of cations , they areexchangeable . For example , cations of potassium ( K+ ) can be substitute ( exchanged ) by cation of Ca ( Ca2 + ) and vice versa .
Thesoil cation interchange capacity(orCEC ) is thetotal turn of cation that a soil can support , which is its total negative charge .
The higher the CEC , the higher the act of negative armorial bearing , and the more cations ( soil nutrients with cocksure charge ) such as calcium ( Ca2 + ) , magnesium ( Mg2 + ) , potassium ( K+ ) , ammonium ion ( NH4 + ) that can be held .
What Is the Measurement Unit for CEC?
Soil CEC is measured inmillequivalents per 100 grams of soil(meq/100 g ) which is a measurement ofconcentration , the amount of something present per unit volume .
One meqis a measure of the number of ion that are required to add together up to a quantity of about 6 x 1020positive electrical tutelage .
The amount of alimentary ion required to make up one milliequivalent ( 6 x 1020positive charge ) decreases as the amount of charge they bear increment .
Listed below are rough-cut territory alimentary cations , with the quantity ( weight per Akko ) necessitate to equal a concentration of 1 meq/100 thousand :
Soil Types and CEC
The CEC of a grunge is now related to the grunge ’s composition . Soils that have a high-pitched sand content have low CEC note value . As the clay , silt and organic matter tier of a soil increase , the soils have an more and more higher CDC .
Since a grunge ’s CEC comes from its clay and organic matter mental object , it can be estimated from looking at the soil texture and color .
Normal Range of CEC Values for Common Colour / Texture Soil Groups
Soil pH Stability and Buffer Capacity
In chemical science , a buffer ( buffering agent ) is a weak acid or weak base ( alkali ) in aqueous solution ( break up in water ) that has a extremely unchanging pH , so if an dose or a base is added to a buffer resolution , its pH will not alter importantly .
likewise , land also resists change in pH to keep stable consideration . The buff capacity of soil is defined as a soil ’s power to maintain a constant pH level when an acidifier or alkalizer is added to it .
A soil ’s buffering capability ( its power to maintain a stable grease pH ) is pertain to its CEC ( cation exchange content ) . How this works is explain below .
Soil CEC and Buffer Capacity of Soils
As previously mentioned , a buffer ( buffering agent ) which brace the soil pH and protect it from extreme changes is either a rickety acid or weak base ( alkali ) .
cation can be relegate as either acidic ( window pane - form ) or basic ( alkaline - take shape ) .
grease particle have exchange web site on their control surface which which bond cation . If the cation in the soil water ( which are free and not bound ) are taken up by plant root , or lost through leaching , the cations that are bound on the soil ’s exchange sites can act as a source that can resupply them back into territory water .
The higher the soil CEC , the more acid - form and alkaline - form cations it is able to supply to which carry out the buffering function , and this is refer to as the soil ’s buffer capacity .
The Effect of Soil CEC on Herbicides
Many herbicide such as glyphosate , 2,4 - D , dicamba , and others are weak acids , they have a atomic number 1 ( H+ ) ions into their molecular construction . Other weed killer , under sure conditions , also can incorporate hydrogen ion ( H+ ) into their molecular anatomical structure . Atrazine for exemplar , is achromatic in billing when the soil pH is above 7 , but when the grease pH fall below 7 , it can nibble up hydrogen ( H+ ) ion from the grease solution and take on a irrefutable charge .
Since these positively charged molecule are also cations , they too can be bound to the negatively charged ground particle of organic issue and clay , much the same manner that grease nutrients are .
As the dirt CEC growth , more herbicide is bound to bemire particles , leaving less available in the soil result that plants can take up to be poison by .
As such , many weedkiller software rate are also CEC dependent , vary with the type of soil . That is why the recording label suggest using lower practical app rate on coarse - textured ( sandy ) soils , and higher app pace on all right - textured ( clay and silty ) ground .
Some herbicides are just not used on soils gamey in organic matter because the high CEC of constituent soil binds the weed killer so tightly that it becomes unavailable and is furnish ineffective .
The other problem with herbicides tie to dirt particles is the increase potential forherbicide carryover . herbicide tied up in the territory are not taken up by industrial plant , and show decreased losings through leaching stain water and volatilisation into the atmosphere .
This think of that more of the herbicide is held in reserve in the grunge , and depending on the half - life of the weedkiller , may possibly be released at a later point in time , to injure susceptible / sensible crops embed in that grunge in the hereafter .
broadly , average and fine - textured ( silty and cadaver ) grease that arrest more than 3 % organic thing ( in other words , racy , fertile soils that can hold the most nutrient , and best bread and butter industrial plant outgrowth ) have the gravid potential to hold fast or halt herbicides that can injure future weedkiller - sensitive craw . This puts Fannie Merritt Farmer who take to expend toxic weedkiller in a quite a dilemma , as the dearly-won on-going disbursal of herbicide use for appliance also means with child expenses in chemical fertiliser to by artificial means add on pitiable soils with miserable food - take hold ability , and without a goodly grease ecosystem ( which ask organic thing to function ) , plants are more prostrate to pests and diseases , want further consumption in pesticide and antifungal .
By empathize the soil science , we can see how it ’s easy to build healthy dirt , and workwiththe land alchemy and ecology to acquire good for you plants . That ’s what nature has been doing for over 460 million year , it ’s grounds - based horticulture , so we bed it works .
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