Hi Dear colleague, 

Ilyass , it's good to mention that calcium with its floculation power and it's abundance in these salt affected soil is found in other mineral, we should also study their relative solubility to assess their contribution in soil structure formation for example. 

Anoop, we have discussed  an inquiry about the relation between CaCO3 and  Chlorosis, but here, my perspective behind my question is that floculation is not sufficient in the improvement of soil structure as stated very well in one paper of J.P.Quirk " Aggregation is floculation Plus" and the plus can be organic matter, type of clay,  sesquioxydes of iron and AL and of course calcium carbonate. and i want to find out in what extend the calcium carbonate in a sodic soil assist the soil in a reclamation process? 

I said that because  we have some experimental result about soil hydraulic conductivity change when the exchange between Na-Ca takes places. and the theory said that when Na is flush out from the soil system and we have only Calcium , There will be an improvement in physical properties (i measue Soil hydraulic conductivity to assess this improvement). and in our case , we didn"t found full recovery of soil hydraulic conductivity. So this is why may be the Plus in the statement of J.P.Quirk is the key to understand the Aggregation process in sodic soil reclamation. 

Very interesting question Louadj. Infact , sodic soils having high calcium carbonate content still have poor physical condition , because the exchangeable sodium ions outnumber the calcium ions , thereby , creating a soil condition  saturated with predominantly sodium . These sodium ions later facilitate dispersion of soil clays.  (Such dispersion is largely governed by the type clays present in a given soil . Usually , smectites are most dispersed followed by illites and kaolinites) , contrary to role of calcium ions in  flocculation of clays . this si the reason , despite caicium carbonate present in  sodic soil still has poor physical condition .  

thank you dear Dr Srivastava, 

What if in sodic soils rich in calcium carbonate , it's not the content that is important but the fraction ( Sand , Silt, Clays ) with which calcium carbonate is linked that have an effect on the behavior of these soils ?.  because presumbly, if calcium carbonate is mostly found in the clay fraction , it's can conter act the dispersion of the clays isn't? In the contrary, when Calcium carbonate is in the Silt and Sand fraction, maybe it will accentuate and worsen the effect of sodium on the physical properties!.

Hello Dear

Generally, Calcium in soils is found mainly in minerals such as feldspar, calcite, dolomite, apatite, and hornblende, Calcium sulfate (gypsum) and calcium carbonate (calcite). For the role of calcium carbonate, it's important to have an idea on acid-neutralizing value of soils materials [ it's expressed in terms of calcium carbonate equivalent (CCE).]

I remember on the same  platform , earlier also , we discussed on the role of calcium carbonate in calcareous soils , whether or not , the calcium carbonate particles act as an alternative clay fraction ? . Possibly same stands true here for salt affected soils having ample calcium carbonate . i agree with Tabrika , it is the same exchangeable sodium vis-a-vis other exchangeable  cations , defined as exchangeable sodium percentage in some kind of  equilibrium with sodium adsorption ratio . But , the role calcium carbonate in sodic soils is belittled by dominance of sodium , either in soluble form or in exchangeable form .  

Hi Dear colleague, 

Ilyass , it's good to mention that calcium with its floculation power and it's abundance in these salt affected soil is found in other mineral, we should also study their relative solubility to assess their contribution in soil structure formation for example. 

Anoop, we have discussed  an inquiry about the relation between CaCO3 and  Chlorosis, but here, my perspective behind my question is that floculation is not sufficient in the improvement of soil structure as stated very well in one paper of J.P.Quirk " Aggregation is floculation Plus" and the plus can be organic matter, type of clay,  sesquioxydes of iron and AL and of course calcium carbonate. and i want to find out in what extend the calcium carbonate in a sodic soil assist the soil in a reclamation process? 

I said that because  we have some experimental result about soil hydraulic conductivity change when the exchange between Na-Ca takes places. and the theory said that when Na is flush out from the soil system and we have only Calcium , There will be an improvement in physical properties (i measue Soil hydraulic conductivity to assess this improvement). and in our case , we didn"t found full recovery of soil hydraulic conductivity. So this is why may be the Plus in the statement of J.P.Quirk is the key to understand the Aggregation process in sodic soil reclamation. 

Exactly Louadj ,  you need to check the final  soil ESP , and this ESP whether or not , sufficient  to induce normalcy in hydraulic conductivity of soil , will largely depend upon the soil mineralogy  coupled with particle size distribution . Yes , you are right ,  under such condition , secondary precipitation of Ca into calcium carbonate , you cannot rule out , unless  sufficient reduction in ESP-driven soil pH  disallows any such reaction to take place ?

you are right Anoop, i must check out the final ESP, and the nature of clays will influence the outcome especially if it's high reactive clays like montmorillonite ( in my case i have interstratified clays). but the interesting part as you mention, may be there is some secondary precipitation of calcium carbonate, and in this case , the calcium added won't participate in the reclamation process. 

I appreciate the good question of Dr. Yacine and equally good discussion by colleagues.The structure or physical behavior of soil depends on chemical nature and environment.Both calcareous soils and sodic soils  are problematic soils-for different reasons.Of course, soil structure is not a problem  in calcareous soils(chemical environment and nutrients constraints are problem).In calcareous sodic soils both physical structure and chemical environment are problem.As I understand it is an interplay of calcium carbonate phase equilibrium and the relative abundance of Ca and Na ions  which will play great role in these soils.The major point is solubility of Ca CO3-more soluble in pH range of 6.2-6.50 and least soluble beyond 8.5. The sodicity problem also starts from the same critical pH( both processes start from around pH8.2-8.3).When CaCO3 is not soluble or least soluble it can not provide Ca ions to replace Na from exchange positions or flocculate the clay for facilitating aggregation.So it can not improve soil structure.

The release of Ca ions from insoluble calcium carbonate  is facilitated by the organic matter/root action and moisture content.In calcareous sodic  soils it possible to release C,Mg ions under saturation and submergence as in paddy system.These divalent cations can replace Na from exchange sites and lower the ESP of soil.One method of amelioration of sodic soils is through phytoremediation-through plant root action that helps dissolve native CaCO3 to supply Ca ions for re placing Na ions from exchange complex(without application of amendment).Application of organic manures can also similarly solubilize  CaCO3. Rice(waterlogged)-wheat cultivation under  irrigation has potential to reduce the sodicity problem over long time,say 8-10 years without any chemical amendment.Good work has been done at CSSRI,Karnal,India.

By regulating or controlling H2CO3 ion concentration in irrigation water one can regulate the precipitation of Ca ions and formation of Na2CO3 which in turn provides the Na ions to replace Ca from exchange complex.Residual carbonate is one criterion for judging quality of irrigation water.This sets the stage for formation of sodic soils.The H2CO3 is dominant ion species in soil in pH range 6.0-over 8.0. and one way controls the concentrations of Ca and Mg on one side and Na on the other. Arid environment facilitates the precipitation of CaCO3.

Please read HCO3 in place of H2CO3 in line one and six of last paragraph of my  previous reply/comments.

Thank you Dr Rao for adding interesting information of the discussion about the physical behavior of Calcareous sodic soils. So Bicarbonate ion must be taking into acount in assessing the reclamation process. 

Adding Calcium carbonate in clay soils would be still dangerous than in loam or sandy soils unless soil pH crosses 8.2 for dispersion of clay.