Characterisation and management of salt affected soils (1)

saline and sodic soil

1. Characterisation and management of salt affected soils of Tamilnadu

2. SALT AFFECTED SOILS When salts more soluble than calcium carbonate and gypsum are present in the soil and affect crop growth and yield of most crops these soils are considered salt affected. In 1954, the US Salinity Laboratory grouped salt affected soils in to Saline soil Alkali soil Saline –Alkali Due to the effect of two common kind of salts (neutral and alkali salts) it is grouped in to saline and alkali soil

3. Salt Affected Soils – Occur when rainfall is not sufficient for adequate leaching of salts – Common in arid regions – Can ruin soils for agriculture Common salt ions • Ca 2+ , Mg 2+ , Na + , Cl - , SO 4 2- ,HCO 3 - ,CO 3 2-

4. Classification EC (dSm -1 ) pH ESP Saline soil >4 <8.5 <15 Alkali soil <4 >8.5 >15 Saline soil / Solonchak Alkali soil/ sodic / Solontez Salt affected soil - Classification

5. The salt-affected soils account for 6.727 Mha equivalent to 2.1 % of the geographical area of the country. Out of the total 6.727 million ha of salt-affected soils, 2.956 million ha are saline 3.771 million ha are sodic . Salt affected soils in India

6. a) Chemical Characteristics i ) EC of the saturation soil extract is more than 4 dSm -1 ii) pH of the soil is less than 8.5 (< 8.5) iii) ESP is less than 15 (<15) b) Physical Characteristics i ) Soil Structure- Usually good ii) Infiltration rate- High iii) Soil Aeration- Good iv) Colour - Usually white SALINE SOIL - Characterization

7. Concentration of neutral salts( Cl - , SO 4 2- ) is higher than alkali salts(HCO 3 - ,CO 3 2- ) Characterised by saline efflorescence, white encrustation of salts at the surface. Salts raise the osmotic potential of the soil solution reduces available soil water Plants have to use more energy to get the water they need SALINE SOIL- “White Alkali” soils

8. The process by which the saline soil formed is called Salinization . Saline soils occur mostly in arid or semi arid regions. In arid regions - due to less rainfall and high evaporation rate which tend further to concentrate the salts in soils and in surface waters. Saline soil - Formation

9. Stunted growth Wilting Bluish-green color Necrosis of leaf tips Drought stress symptoms Specific toxicities eg . Boron Plant species vary in salt tolerance Salt injury - High salt levels when high rates of fertilizer or manure applied Effects of saline soil on plants

10. a) Chemical Characteristics i ) EC of the saturation soil extract is less than 4 dSm -1 ii) pH of the soil is more than 8.5 iii) ESP is higher than 15 b) Physical Characteristics i ) Soil Structure - very poor (soil is in highly dispersed condition) ii) Infiltration rate - very poor iii) Soil Aeration - very poor iv) Colour - Usually black Alkali Soil - Characterization

11. Alkali Soil - “Black Alkali” soils Concentration of alkali salts(HCO 3 - ,CO 3 2- ) is higher than neutral salts( Cl - , SO 4 2- ). Main problem is the effect of sodium on flocculation and aggregation of soil particles Sodium causes the soil particles to disperse No aggregation of soil particles Individual clay particles clog soil pores Poor soil physical properties

12. Alkali soil -Formation

13. Effect of Alkali soil on plants

14. Management of Salt affected soil

15. Physical measures 1. Leaching : When soil elements after dissolving with water go down from upper parts to the lower level, it is called leaching. In this method, saline elements of the soil are transferred to lower levels after dissolving with water. This water, along with the supply of water to crops, takes away salts after dissolving them. That is why more water is required in this method.

16. Scratching : Many times the salts are collected in a large quantity and it looks like a heap. Then it has to be scratched out from the field to reduce salinity of the soil. This method not practicable on a large scale. Drainage : With drainage of additional water, concentration of salts does not take place. Drains may be constructed in the field so that excess water keeps on discharging.

17. Chemical Measures Reclamation of alkali / sodic soils requires neutralization of alkalinity and replacement of most of the sodium ions from the soil – exchange complex by the more favourable calcium ions. 1. Solvent Calcium Salt : Gypsum and Phospho Gypsum 2. Little Soluble Calcium Salt : Lime Stone 3. Acid and Acid Producing : Sulphur , Acid of Sulphur , Pyrites Gypsum is the most commonly used chemical amendment.

18. Soil management measures Preparation of the Field Fields should be kept leveled . Water distribution during irrigation is balanced in leveled field which prevents concentration of salts. Preparation of Basin and Sowing Sowing of crop should be done on the slope by following furrow and basin method. In basin irrigation, the salt collects near the basin, the adverse effect of which is visible on plants. Special attention should be given to irrigation. Reduction in Evaporation Growing of Crops Bearing Salts and Alkali condition

19. Reference R. K.  Gupta , I. P.  Abrol , Salt-Affected Soils: Their Reclamation and Management for Crop Production, Advances in Soil Science vol. 11 pp. 223-288. http://www.fao.org/docrep/x5871e/x5871e03.htm