Some researchers found gypsum amendment is a way to reduce salinity, but it is not suitable for all types of soil. Some researcher reported that ash from rice straw and rice husk may mitigate soil salinity, someone oppose this findings. So, which amendments are better for saline soil?
Dear Dr. Islam,
(1) The use of chemical amendment as source of Ca, which tend to replace exchangeable Na, as well as soil irrigation with water rich in divalent cations are strategies for soil saline remediation, but in dry soils with basic pH, soil amendment with organic residues could also be a good strategy. Recently, various organic amendments such as mulch, manures and composts, have been investigated for their effectiveness in soil remediation. It has been demonstrated that the application of organic matter to saline soils can accelerate Na+ leaching, decrease the exchangeable sodium percentage and electrical conductivity and increase water infiltration, water-holding capacity and aggregate stability. Furthermore, the application of organic matter increases soil microbial biomass and some soil enzymatic activities such as urease, alkaline phosphatase and β-glucosidase.
(2) The effectiveness of adding two organic wastes (cotton gin crushed compost, CGCC, and poultry manure, PM) to a saline soil (Salorthidic Fluvaquent) in dryland conditions was studied by Tejada et al. (2006) during a period of 5 years. Organic wastes were applied at rates of 5 and 10 t organic matter ha−1. One year after the assay began, spontaneous vegetation had appeared in the treated plots, particularly in that receiving a high PM dose. After 5 years the plant cover in this treated plot was around 80% (compared with the 8% of the control soil). The effect on the soils physical and chemical properties, soil microbial biomass, and six soil enzymatic activities (dehydrogenase, urease, protease, β-glucosidase, arylsulfatase, and phosphatase activities) were ascertained. Both added organic wastes had a positive effect on the physical, chemical and biological properties of the soil, although at the end of the experimental period, the soil physical properties, such as bulk density, increased more significantly in the CGCC-amended soils (23%) and the exchangeable sodium percentage (ESP) decreased more significantly in the CGCC-amended soils (50%) compared to the unamended soil. Water soluble carbohydrates and soil biochemical properties were higher in the PM-amended soils compared to the CGCC-amended soils (by 70% for water soluble carbohydrates, and by 34, 18, 37, 39, 40 and 30% for urease, protease, β-glucosidase, phosphatase, arylsulfatase and dehydrogenase activities, respectively). After 5 years, the percentage of plant cover was >50% in all treated plots and 8% in the control soil.
(3) I suggest you to read the following paper for more detailed information on this work:
Tejada M, Garcia C, Gonzalez JL, Hernandez MT (2006) Use of organic amendment as a strategy for saline soil remediation: Influence on the physical, chemical and biological properties of soil. Soil Biology and Biochemistry 38(6):1413-1421.
Gypsum amendment replaces the Na from exchange site as Na2SO4, but Na2SO4 is highly soluble than CaSO4 (gypsum). As a result gypsum amendment increases the Na concentration in soil solution. However, draining of this soluble Na may reduce the effect of soil salinity. On the other hand, application of K rich rice straw or rice husk inhibit the activity of Na in saline soil. Actually if we can increase the K status in soil compare to Na, salinity effects can be mitigated. So far I know, there is no negative effect of rice straw and rice husk or ash application in saline soil. Considering the soil properties, organic amendment with rice straw, ash, husk etc. is better than inorganic amendment of saline soil. However, drainage system should be improved to drain out the soluble salts specially Na and Cl.
I think , combination of both has produced more remunerative response compared to chemical amendment alone . the best strategy would be to use chemical , physical and microbial/biological amendments for integrated reclamation of salt affected soils , however , strong strategic difference difference is observed with regard to reclamation of saline soils versus sodic soils.
Apply molasses or even go for green manures like sunhemp, diancha, etc and incorporate in the affected soils.
We also found some positive results with green manuring (Dhaincha) and ash amendment to reduce the salinity effect on crop growth and yield.
I think rice straw incorporation in soil may have positive impact on saline soil improvement. There are some reasons, I think, rice straw enrich with K so it might be beneficial for plant in saline condition. secondly, rice straw can act as mulches, which may reduce evaporation resulting in minimum upward movement of salt. Finally, it can plays a vital role as organic matter. Beside this, we can apply gypsum with rice straw. Because it can replaces Na+. I also found gypsum gas positive effect on saline soil improvement. Therefore, I believe combination of rice straw with gypsum may improve saline soil. I desire comments and suggestion from all of you about my concept.
M. N. Islam
I think the the type, rate, method of application, choice of crops and economics of amendments will depend upon the soil and irrigation water characteristics along with the climate.
If the soil is medium texture and calcareous with low to moderate salinity (EC), simple leaching will be enough. However, addition of OM in any form (FM, GM, Crop residues, PM, etc) are always useful under arid climates, especially in fine textures to maintain soil drainage.
If the soil is medium texture and calcareous with high salinity (EC), simple leaching will help formation of sodic conditions and here simple leaching will not be enough. Therefore, a Ca source is required. Addition of OM in any form (FM, GM, Crop residues, PM, etc) are always useful under arid climates.
For saline-sodic and sodic soils, an external source of Ca (gypsum being the most economical) is must for economical soil improvement within 2-3 years. If the soil is moderately to strongly calcareous, then 20-30 % acids or acid formers along with gypsum can be used to shorten the period of reclamation but cost will increase.
In most of the situations, initially relatively poor quality irrigation water is beneficial through its better effects on soil HC; with time gradually shift to better quality water.
Excellent discussion dear MN Islam. High K in rice straw helps to reduce the Na activity in saline soil and also inhibit the Na uptake by plant as Na and K are competitive ions in the soil-plant system.
Dear colleagues look at the following reactions where X stands for soil:
CaX + Na2 ↔ Na2X + Ca↓ ------------- sodication as per Gapon or Vanselow eqs.
Na2X + Ca ↔ CaX + Na ↓------------- desodication as per Gapon or Vanselow es
Now any soil-water-plant system promoting soluble Na will be inducing sodication and that increasing Ca will help soil desodication, especially under arid region irrigated soils.
I think you can used bio-char as a organic source for saline soil
In salt affected soils, potassium does have some ameliorative role due to competing ionic size and hydration capacity as well...
Dear Dr. Islam,
(1) The use of chemical amendment as source of Ca, which tend to replace exchangeable Na, as well as soil irrigation with water rich in divalent cations are strategies for soil saline remediation, but in dry soils with basic pH, soil amendment with organic residues could also be a good strategy. Recently, various organic amendments such as mulch, manures and composts, have been investigated for their effectiveness in soil remediation. It has been demonstrated that the application of organic matter to saline soils can accelerate Na+ leaching, decrease the exchangeable sodium percentage and electrical conductivity and increase water infiltration, water-holding capacity and aggregate stability. Furthermore, the application of organic matter increases soil microbial biomass and some soil enzymatic activities such as urease, alkaline phosphatase and β-glucosidase.
(2) The effectiveness of adding two organic wastes (cotton gin crushed compost, CGCC, and poultry manure, PM) to a saline soil (Salorthidic Fluvaquent) in dryland conditions was studied by Tejada et al. (2006) during a period of 5 years. Organic wastes were applied at rates of 5 and 10 t organic matter ha−1. One year after the assay began, spontaneous vegetation had appeared in the treated plots, particularly in that receiving a high PM dose. After 5 years the plant cover in this treated plot was around 80% (compared with the 8% of the control soil). The effect on the soils physical and chemical properties, soil microbial biomass, and six soil enzymatic activities (dehydrogenase, urease, protease, β-glucosidase, arylsulfatase, and phosphatase activities) were ascertained. Both added organic wastes had a positive effect on the physical, chemical and biological properties of the soil, although at the end of the experimental period, the soil physical properties, such as bulk density, increased more significantly in the CGCC-amended soils (23%) and the exchangeable sodium percentage (ESP) decreased more significantly in the CGCC-amended soils (50%) compared to the unamended soil. Water soluble carbohydrates and soil biochemical properties were higher in the PM-amended soils compared to the CGCC-amended soils (by 70% for water soluble carbohydrates, and by 34, 18, 37, 39, 40 and 30% for urease, protease, β-glucosidase, phosphatase, arylsulfatase and dehydrogenase activities, respectively). After 5 years, the percentage of plant cover was >50% in all treated plots and 8% in the control soil.
(3) I suggest you to read the following paper for more detailed information on this work:
Tejada M, Garcia C, Gonzalez JL, Hernandez MT (2006) Use of organic amendment as a strategy for saline soil remediation: Influence on the physical, chemical and biological properties of soil. Soil Biology and Biochemistry 38(6):1413-1421.
Practically saline soils are as as productive as normal soils if excess soluble salts are removed through leaching with good quality water. As such organic and/inorganic amendments are not required for practical field conditions in saline soils.
Dear Mahapatra,
I completely support your thinking but good quality water is not available in saline area.
Dear Islam, I hope you may have participated in the biochar discussion which has taken a long time. In addition to multiple advantages in improving soil quality, one of the advantages of biochar is in the rehabilitation of degraded lands and remediation of contaminated soils, including saline soils. Gypsum is, in fact, an inorganic amendment used to remedy salt affected soils.
Some time a go, I read a paper about growing plants/crops that can reduce salt from soil and the report showed that salt was decreased after trying those selected plants.
Yes, Endalew, for example, Prosopis sp. is one of salt tolerant plant species that can reduce salinity. This has been tested in the saline areas of Awash irrigated land in Ethiopia.
Mr. MN Islam, you rightly mentioned that there is a scarcity of fresh/sweet/good quality water in saline areas. But during monsoon, a lot of rain water is available and it can be stored in pond near the field. Or pond can be dug for fresh water conservation. This water can be used for irrigation purpose. However, farmers should be intelligent enough to preserve and use fresh water in that area.
Dear Agegnehu,
Than you so much. It is a good idea. So, in that case what will be the raw material? Rice husk, rice straw may be used for that, I think. What about your comments/suggestions?
The question has not been rightly asked. There are three categories of salt affected soils; saline (only soluble salts are more than 4 dS/m), Saline sodic (EC > 4dS/m and ESP > 15 or SAR > 13) and sodic (EC< 4dS/m but ESP > 15 or SAR >13). Saline soils need no amendment for reclamation except leaching of soluble salts with good quality water while sodic and saline sodic soils need amendments for their reclamation. Therefore, terms should be used appropriately.
Therefore, either the general term salt affected soils (not saline soils) or specifically sodic or saline sodic be mentioned whenever you are going to speak of amendments (organic or inorganic).
Mr. Islam,
Dr. Hussain is right. There are three classes of salt affected soils. However, I am assuming you are specifically interested in saline soils (ECe > 4dS/m and ESP < 15). As mentioned in the comments, leaching may be an option. Here a a few things to consider if you are thinking about leaching; leaching requirement, irrigation timing, location of salts in the profile and spatial variability of the field. Hope this helps
The first question you must ask is "what is the source and chemical suite of the salt?". If you have a perched water table (transient salinity - see a paper by Pichu Rengasamy on this) then your approach will be different to a free draining soil.
if the salt is dominantly a monovalent cation salt (Na or K) then both of these will add to dispersive potential of the the aggregate. I say potential because the salinity actually has a positive effect on compressing the diffuse double layer (offsetting monovalent cation effect) via osmotic pressure. In this circumstance, reducing the salinity will exacerbate the likelihood of dispersion. However, the threshold point where the cation effect overcomes the osmotic pressure (threshold electrolyte concentration) is soil specific, even within the same soil order.
hence, to address salinity, we must consider, the salt source, the chemistry of the salt, and the threshold electrolyte concentration. If the monovalent cation effect on structure is demonstrated as minimal for your soil, or the salt is Ca or Mg dominant, then leaching of the soil profile to move salinity further into the profile will work for free draining soil. If a low permeability layer exists, then physical manipulation of this might be required, or a fresh water quality used to dilute salts adn move them laterally. However, rapid dilution can disperse even relatively stable soils. So the process should be done gradually and preferably using unsaturated flow.
If the soils are likely to disperse as salinity is reduced, a source of Ca can be applied to reduce the Na and K effect. However, if the source salt is alkaline (carbonate or bicarbonate species) then the Ca will be removed by excess alkalinity (as the soil alkalinity increases, the pH will also), precipitating out as a carbonate. In such cases a source of acid is also required.
Much of this is explained in my work. See:
Bennett and Raine 2012
Ezlit et al 2013
Bennett et al 2014 lime + gypsum dry land
Bennett et al 2015 a and b lime + gypsum irrigation
Bennett et al 2016 Land amendment of sodic and alkaline irrigation
It is also worth noting that we have updated dispersive parameters to account for dispersive effects of other cations. See:
Rengasamy and Marchuk 2012 Cation Ratio of Structural Stability (replaces SAR)
Bennett et al 2016 Exchangeable dispersive percentage (replaces ESP)
finally, you might find the free version of HYDRUS 1 D useful in planning your amelioration, especially when coupled with PHREEQC geochemical model.
Thank you Dr. Haruna and Dr. Bennet for explaining the processes of reclamation further.
Dr.Islam- Please refer some of the literature published by the ICAR-CSSRI institute at Karnal,India. Some of their reclamation practices on saline soils of West Bengal coastal areas may be applicable to your soils.
Dear Dilip Kumar Pal,
Thank you so much for your nice suggestion.
A very good explanations provided by Dr. Dilip Kumar Kundu and Dr. John.
Dear Islam,
Biochar application and growing salt tolerant people like Prosopis sp., can be considered as biological remediation of saline soil as discussed widely here. The research articles attached here may be useful regarding biochar application for remediation of saline soil.
Simply remove the excess soluble salts through leaching. Additional biochar will help improving productivity.
Gypsum and other soil conditioners work usually depend on the availability of good-quality irrigation water in addition to a good drainage network for the leaching process... What if this water is not available or in a lower quality... What if the soil has heavy texture ... .. I think that the removal of salts from the soil is a hydrologically and financially heavy cost process... And the most appropriate action is to keep the salts in the soil, but in an idle status with no possibility of a quick return to the active status again ..... DOPSA is definitely the best solution... It reacts very quickly with all active cations of salts in the soil in presence or absence of water and deposited it in an insoluble form in strong acids, bases, hot water as well as organic solvents
We should not confuse the management of salinity with sodicity. Gypsum will effectively reduce sodicity but not salinity. If the soils are both saline and sodic the amelioration of sodicity must preceed the leaching of salts to reduce salinity.
Organic amendment with rice straw, ash, husk etc. is better than inorganic amendment of saline soil. However, drainage system should be improved to drain out the soluble salts specially Na and Cl.
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