Ca (gypsum) application reduces Na content in salt affected soil but due to poor drainage gypsum amendment might not be properly effective. Therefore, gypsum application with subsoil drainage might be the best option for reducing salt. So, I need to know which method is most suitable for subsoil drainage.
You can use perforated pipe below the root zone depth so that excess Na can be drained out through the pipe. Of course you have mini pond near the field where the drained water be accumulated.
Thank you sir (Dr. Aminul Islam) for your nice suggestions. If we can develop concrete drain in the field, it might be useful to drain out the salt (Na).
Please get the 0-100 cm weighted mean value of the saturated hydraulic conductivity data of the soil profile first and get the same data after adding gypsum. The difference may suggest you which method to apply. Moreover be sure about the presence of soluble carbonate and bicarbonate salts vis a vis chloride and sulphate. In case former two are more than the latter then surface application of gypsum will be appropriate before transplanting rice crop. Please get some information on the similar lines from ICAR-CSSRI, Karnal, India website.
Thanks Dilip Kumar Pal sir for your good suggestion. Saturated hydraulic conductivity of soil is an important factor for selecting drainage system.
gypsum is quite insoluble in water (0.3g/litre) and is unlikely to move once spread on the surface. So its effects are usually confined to surface soil. One way to fix this is to deep rip every 2m and inject gypsum into the rip. (use 'air seeder' if gypsum is a fine powder or make up a slurry and inject as a liquid )
An alternative is to use a soluble form of calcium (CaNo3 , or Ca Cl2) both are soluble at 3000g/litre and move where irrigation or rainfall goes. ie hopefully into subsoil.
Ca No3 is preferred as it has nitrogen bonus. beware CaCl2 is sometimes extracted from furnace ash and may have cadmium. Both are more expensive than gypsum but being 100x more effective, you dont need as much.
Use Sub Surface Drainage Technology (only for waterlogged saline soil), for that you may contact with Dr. D.S. Bundela or Dr. S.K. Kamra (most suitable person)
Responses suggesting tile drainage may be valid but the drain pipe solution is extremely expensive. CaNO3 is EXTREMELY effective in all but the worst cases. Recommend you purchase 20kg of Ca NO3 and do a small plot trial . Make a bund around (say) 2 plots of 5mx 5m area - treat one with Ca No3 at 2kg/m2 (20t/ha) - other plot is a control. Flood both and measure infiltration rate. Trial is simple and cheap and has a good chance of working. If you are trying to 'sell' the idea to farmers then make the same plots and flood them, but dont add the CaNO3 until after the water has been added - the result is often spectacular.
I would like to thank you Islam for such important question, first of all it is important to know the different between saline (salt are in soil solution) and alkaline or sodic soils (when Na in the soil complex), so for saline soils and depending on type of salinity, the drainage in the efficient way to reduce, but in case of having high rate of exchangeable Na in the soil complex so the pH of the soil abstract is very high and need to be reduced, so we need to use some kind of calcium contented matter such as gypsum or some pH low-matters such FeSO4 or even concentrated H2SO4 to extract the Na from soil complex to be dissolved in the soil solution and later removed by leaching it out using some type of drainage (horizontal or vertical) depending on geomorphological conditions of soil we choose the type of drainage. the Norm of Gypsum, that should be used, depends on the Na concentration in the soil complex and there is special formula for calculation. Hope I could give some answer for your question
Please check the link to know more about sodic soils:http://www.fao.org/docrep/x5871e/x5871e05.htm
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