There are some kinds of salt present in saline soil. As far I know, Na salt is more harmful than others. But I have no idea about effect of Mg salt (MgSO4) on soil health. What are the permissible limits of Mg salt for rice cultivation in saline soil? It is notable that texture of soil silt loam or clay loam.
When Mg ions is greater than Ca ions, soil structural stability may be disrupted. Mg ions may be dominated and binding effect of Ca may be suppressed.
Please have a look at this researchgate link and PDF attachments.
https://www.researchgate.net/post/Why_do_salt_affected_soils_continue_to_pose_potential_threats_to_food_security
Hi
The effect of Mg ions depends very much on balance of other cations, but an imbalance of Mg can be detrimental. In terms of nutrition, if the Ca:Mg balance is low approaching or less than 1, this can cause Ca deficiency. A high proportion of Mg on the cation exchange complex and a low Ca:Mg ratio can also result in dispersion of clay particles in soils that are already sodic (ie it tends to worsen the effects of soil sodicity). This may or may not be a problem in your soil if salinity is high enough to control dispersion. This latter issue would be more of an issue in a clay loam with higher clay content.
When Mg ions is greater than Ca ions, soil structural stability may be disrupted. Mg ions may be dominated and binding effect of Ca may be suppressed.
The sulphate anion can induce the lixiviation of Na and improve saline soils. MgSO4 has a low salinity index and will not cause problems if you use it correctly.
For improvement of saline soils better use CaSO4, cause its far cheaper and has a lower salinity index than MgSO4.
Calcium have more power to dislocate Na from the cation exchange complex to the soil solution.
Dear MN,- You can expect the effect of Mg ions in dispersion of clay particles if saline soils are calcareous having pH around 8.0 or just less than 8.5 under SAT environments.
The saline soil is high in Na which scatters soil particles and destroy soil structure and other soil physical properties but Mg is an alkaline earth metal and binds the soil properties through its floculating property which impacts soil moisture ret ention , temperature but the soil pH must be determined to know the qua ntity of Mg to apply to maintain soil equlibrum
Nice discussion...Here an excerpt of an excellent work ..comparing the effect of magnesium versus calcium considering critical flocculation standard (CFS) , which showed magnesium has more dispersive power than calcium. CFS was higher in magnesium than calcium in soils ..? PDF enclosed for further reading ...
Most of the answers are on correct direction. However, it is important to note that negative effects of MgSO4 will only occur when it is in excessive quantities otherwise Mg is also helpful in replacing Na and improving physical properties. One thing more is important that MgSO4 is highly less soluble salt.
Yes Nazir Hossain, you correctly mentioned that Mg is helpful to replace Na from exchange sites and also play role to improve soil structure. MgSO4 is less soluble than Na2SO4 salt but more soluble than CaSO4 salt.
Amount of soluble Na ions is generally much higher in saline soils (ECe >> 4 mmhos /cm). Amidst such high concentration of Na, it is difficult to guess what will be the effect of Mg ions. Some experimental set up may resolve this issue. In natural soil system nothing is recorded yet I guess.
Interesting discussion on the effect of MgSO4 on physical properties of soil.As pointed out by Dr. Nazir and Dr.Pal,in normal condditions, the Mg ion concentration may not be higher than Ca.Also the dominant ion in saline or saline sodic soils will be Na.The origin for development of saline soils is the quality /composition of irrigation /ground water.The following paragraph from a standard soil chemistry book well explains the conditions under which Mg creates problem.
"A notable exception to this general rule is found where the Mg ion concentration in irrigation water or ascending ground water is higher than the Ca concentration.Then an appreciable part of the Mg ion will remain in solution,as the solubility product of MgCO3 under well-aerated conditions may be estimated at approximately10 meq/litre square.This can lead to the formation of so-called' Mg-Na-solonetzes',which have a high Mg saturation combined with an ESP-value below15.Such soils are notorious for their poor physical behaviour.In most natural waters,however, the Ca-concentration surpasses the Mg-concentration.In that case practically all Mg ions may be precipitated in the form of the highly insoluble dolomite :CaMg(CO3)2"
Soil Chemistry A.Basic Elements Edited By Bolt,G.H. and Bruggenwert,M.G.M Elsevier Scientific Publishing Company Amsterdam 1976.p184
Yes such precipitation of Ca/Mg carbonates happens when pH of the soil solution reaches around 8.2. This means soil water has RSC > 2, indicating the considerable presence of carbonate and bicarbonate ions.In such chemical environments clay colloid is likely to remain dispersed which will obviously impair drainage of soils.Therefore the nature and content of anions will decide the drainage of soils even in saline condition.
Dr.Pal, the conditions (soil pH and carbonate and bicarbonate presence in water) mentioned by your are important.
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