Re-sodification is something that is taking place all the time in nature in arid and semi-arid environments though the magnitude may be very imperceptible. It is now being realized that even small quantities of sodium can bring structural problems. A good remedy is to keep soil organic matter levels at adequate levels. Judicious use of irrigation water and amendments are well known measures.   

I agree with Desiraju Rao that re-sodification is a constant companion when the evaporation rate exceeds the precipitation.

Irrigation water quality can vary much according to the sources available and the use of lower conductivity water is a good way to avoid issues.

Some wells are notably high in salts.

I also agree that soil organic matter levels are very important.

If one uses mature compost rather than raw manures it may be able to reduce the sodic load. I would be interested in some of the latest technologies people are using for sodification management on the subcontinent.

We all remember being at CSSRI for sometime that the institute  always advocates  to  reclaim sodic soils with gypsum and planting rice crop as the first crop and also to keep  reclaimed sodic soils under  constant cultivation  so that re-emergence of sodicity is restricted  under SAT environment. If such practice is discontinued re-emergence of sodicity will occur in SAT environment as the regressive pedogenic process.

The use of gysum has been a main stay. The use of Piriformospora indica unique mycorrhizal basidiomycete has been shown to allow barley to greatly improve under saline conditions.

Since conventional fertilizers have high salt content I would think the inclusion of legumes in rotation with rice is something that deserves some thought and attention.

Yes Dr. Hepperley, the use of green manure crops like Sesbania cannabina (local name dhiancha`' in India)  is an essential component of alkali (sodic) soil reclamation, firstly because it adds organic matter, secondly it is highly tolerant to  high ESP and has very vigorous and deep roots which open up the soil and facilitate leaching. What Dr. Pal says is extremely important, which is to keep cropping going continuously so that salts do not come up. In fact the vast tracts of salt affected soils north of Delhi were once thick forests in Mughal times (see The Indian Gazetteer), gradual deforestation then allowed salts washed from uplands to accumulate in the lower basins.

Dr. Hepperly makes another very important point, which is that of the irrigation water quality. If it is very good or when there is rainfall (distilled water) there is bound to be dispersion and crusting leading to further problems. A little bit of salts will facilitate leaching.    

Nicely explained by Dr. DLN.

Thanks @ Dr Pal, @Dr DLN Rao and @Paul Reed Hepperly  for your replies. This is true that enhanced electrolytic concentration of irrigation water enhnce the process of flocullation and increase the permeability of degraded alkali lands. Thanks again,

True Dr. Dubey but irrigation water must not contain CO3 and HCO3ions, and Ca+Mg ion need to be larger than Na ions.

As I encountered in Mahabubnagar district, Telangana the irrigation water with high Na levels than Ca & Mg poses threat to saturated hydraulic conductivity. The sHC of the soils of this region is impaired and the mean rainfall is around 500 mm only. The soil pH throughout the examined pedons are in range of 9.0-10.5 and the yield of cotton and red gram are very low. This region is rainfed with irrigation facilities available in few locations through bore-well water which contains high sodium. Continous cropping is a tough ask here and the soil degradation is being enhanced in this region.

A good account on the menace of using GW as supplemental irrigation in SAT area. Without checking the CO3 and HCO3 content such water must not be used in soils with > 25 % clay.  

Yes Sir Dr Pal. It is true high clay content in soils restrict the use of high RSC waters.. Thanks

 Dear Vasu Duraisamy, High Na is not very bad until it had sufficient amount of Cqa and Mg ions and also neutral salts Cl and SO4. Use of Na rich waters which usually contains alkali salts too (CO3 and HCO3) increase dispersion and these dispersed particles sat in pores and clog the capillaries create  impeded situation. We have to neutrailise the alkalinity of these waters before use or add some amendment in soils to maintain cotton yields, Thanks

Dear Dr. Dubey,

Thanks for the suggestions. In the case which I mentioned the the groundwater is the only source of irrigation and there is no canal or open well available. Interesting fact is that there is no industry also and probability for contamination of water sources is also limited. However, the peninsualr gneissic  complex aquifers in that area have groundwater rich in basic cations along with carbonate and bicarbonate anions.  The ionic sequence is Na>Ca>Mg>SO4> HCO3>CO3. Also, there is occurrence of substantial pedogenic carbonates which may limit gypsum application. Suggestion of green manure may be an option but farmers aren't interested to use limited water to green manures. I invite suggestions on suitable management intervention.

Dear Vasu,

                  Rain-fed agriculture is the only option in SAT clay rich soils that include red and black soils. In such soils  under SAT environment use of ground water often create sodicity in soils. Such examples lie in SAT Maharashtra and the then Andhra Pradesh. It is  very difficult to convince SAT farmers for any conservation method that requires time because they need  quick  good return of their investments to run the livelihood. Use of irrigation  water is partially tenable if such clay soils contain soil modifiers like gypsum and Ca-zeolites. For an elaborate information you may refer to the paper attached. Please refer to  the Section 7.5

Dr. Vasu, Thanks for the information that the SAT soils of Mahbubnagar district have pH as high as 10.5. (i assume you are talking about 1:2 soil-water suspension pH). The highest I measured was 10.6 in Karnal in Haryana. Thanks

Dr. Vasu, Thanks for the information that the SAT soils of Mahbubnagar district have pH as high as 10.5. (i assume you are talking about 1:2 soil-water suspension pH). The highest I measured was 10.6 in Karnal in Haryana. Thanks

Dear Dr Vasu Duraisamy ji, It could have been helpful to me If I could know the concentrations of the salts and/or RSC  & EC of waters before commenting. It is also wise to use water for productive purpose rather than putting more and more water to produce green mannaures. In this case only farmers should use minimum quantity of water as it will further deteriorate soil with every irrigation as rainfall is very low with high ET and leaching of salts are not possible. 

 Thanks to Dr Pal and Dr DLN Rao for sharing their experiences. especially for a link provided by you Dr Pal. Regards

Dear Dr.Pal,

 Thanks for the reference. I hope this will lead me to find a solution.

Dear Dr. DLN Rao,

I measured with 1:2 soil water suspension and in some samples I found it difficult to stir the solution upon adding water such that immediately after adding water clods formed and it felt like soap. Upon stirring for long time (>30 min) it changed to a paste and immersing pH electrode resulted in fluctuations. Also during measurement of sHC by constant head method, there were cracks observed after 5-6 hours in even though there was 4 cm thick water head maintained on soil.

Dear Dr. S K Dubey,

I collected about 50 groundwater samples spread over 20000 ha area and analysed. EC varied from 500 to 5130 uS cm-1. Sodium from 36 to 117  and Ca from 15 to 114, Mg from 11 to 129, carbonate from 0 to 4, bicarbonate from 1 to 17.5 me l-1. 

As you pointed out, the available water can't be used for green manure and there are about 30000 farmers owning 16000 ha cultivated land. Average land holding is 0.45 ha only and they are also resource poor. Hence, finding a solution seems a tough ask. It would be very helpfull if you could suggest me viable options. I am also following the question on alternative to gypsum you posted here. 

Thanks.

Dear Vasu, it seems that your issues are related to the quality of irrigation water.

From your analysis its quality is too high in 1) conductivity, 2) sodium and 3) carbonate. A desalinization of the irrigation water using a solar system would be ideal coupled with the use of water tower circle drip system which would ideally gravity fed and run on solar pumps to the elevated reservoir.

Solar technologies which generate deionization or distillation would seem to have potential use since both of these methods can be employed to reduce  residual salt in solution increasing the quality and value of the residual water for irrigation purpose.

Thankfully in an area of aridity solar resource potential  is both reliable and decentralized. The small farmer base would be ideal of labor intensive vegetable production.

Hopefully an initiative to create a small farm model to show and tell might be solution for this type of issue.

Develop show and tell and then walk with the farmers as they tell their success stories to each other and spread the good news.

Even when water is limited throughout the whole season catchment of water from rainfall can be useful as the rain water does not have salt conductivity or carbonate issues. Rainfall in non industrialized areas is 5.7 pH which is slightly acidic and would be beneficially used for alkaline soil areas as prevalent in many arid and semi arid regions.

I believe you and your colleagues can resolve these issues and share them to many others in the same need.

Best Regards, P

Thanks Paul Reed Hepperly for such an elaborated answer and an Idea to use solar energy to  desalinize it. It is true in arid and semi arid areas  sun light is available in plenty. Thanks

Many Thanks Dr. Paul Reed Hepperly for the innovative options. We will study it and explore the possibility of implementing it.