What is the reason behind the fact that Gupta and Abrol (1990) specified pH(s) < 8.2 for saline and pH(s) > 8.2 for sodic soil of Indo- Gangetic plain?
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Saline and Sodic Soils - North Dakota State University
https://www.ag.ndsu.edu/langdonrec/soil-health/saline-sodic-soils
If the soil conductivity is greater than 4 mmohms the soil will be considered saline. When the soil has 15% of its CEC as Sodium it would be defined as Sodic. When it has greater 4 mmohs conductivity and 15% of its CEC it is Sodic Saline.
The North Dakota State Extension publication is pretty understandable.
Avijit , your question is very good. Probably , this is not the case for classifying the salt affected soils into saline or sodic soils . The role of soil texture and mineralogy is pivotal in fixing up those limits . An ESP of 15 may be good for loam or sandy loam soils , but same ESP of 15 in typical smectite rich clay soils will be equivalent to somewhere 25-30 for loam soils . So , there has been some classical attempts to classify salt affected soils based on soil mineralogy , and reorient these limits depending upon the texture and mineralogy
In this publication pHs refers to pH value of the saturated paste, (which can be made as per usual method to prepare the saturated paste for measuring soluble cations and anions of salt-affected soils) so that they represent near real soil pH of sodic soils (pH > 8.5; ECe > 4 m mhos/cm & ESP>15)at the field capacity moisture. Sodic soil pH at 1;2 soil: water ratio is more of a diluted situation and authors thought it may not represent the real soil pH. Please try to get the Proceedings of the International Symposium Salt-Affected Soils, Karnal,1980. It is available in ICAR/ IARI library wherein you will get the paper in full.
If you have pH greater than 8.2 you will have severe micronutrient deficiency even when the salts and sodium are not elevated.
Depending on the plant species these could include Zinc, Iron and Manganese. All of these will be insoluble at pH of greater that 8.2 contributing to what is seen as a salt or sodium issue but pH is playing a role.
I believe it hard to underestimate the importance of pH related to availability of nutrients the plants will need in their metabolism.
We need to understand the what are the root causes and what are correlated symptoms when dealing with a lot of these challenges.
Is it the salt or is it the sodium or it is pH or is it the combination that are the incitants. How do they interact one with each other? Since there are correlated phenomena going on the inter relationship is not necessarily simple proposition.
Dr Hons I enjoyed your observation.
Dr.Hepperly, your concluding paragraph is important. In the soils having an abundant amount of Ca in solution and exchange sites,handling major or micronutriets is not difficult. Even in calcareous soils having pH
Soluble salts tends to decrease pHs while exchangeable sodium tends to increase the pH. Since in saline soils, soluble salts are present those tend to decrease pHs. The 8.2 pHs limit proposed by Gupta & Abrol (1990) was based on this fact along with their practical experience as they worked very extensively over a long period of time in salt-affected soils.
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