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Script 27.11

Notes to broadcasters

Content:  Some soil is naturally salty.  Other soil becomes that way because of dry weather or too much irrigation.  Here are a few ideas to help you reduce the problem of soil salinity.

Script

Saline soil is a problem for many farmers. Saline soil is especially common in low-lying areas such as the flood plains of rivers, lake beds, and coastal plains. In these places, ground water containing salts is found within a few metres of the surface.

Most plants either do not grow well in saline soil or do not grow at all. They become yellowish and wilted and their growth is stunted. Most plants die in saline soils.

Saline soil kills plants by interfering with the way they get the water and nutrients they need to grow. Plants take up water and nutrients from the soil by a process called osmosis. In the process of osmosis, a weak solution from the soil moves to stronger solution in the roots of the plant. That is how plants feed themselves.

In saline soils, the high salt content makes the soil solution more concentrated than the solution in the roots of the plant–the opposite of the usual situation. So instead of nutrients moving from the soil to the plant, they move from the plant to the soil. The process of osmosis works in reverse. Then the plant dies.

Naturally-saline soils:
Some soils are naturally saline. Areas with naturally saline soil were usually under salt water long ago. Or, there was a high salt content in the rocks and minerals that formed the soil. Areas with naturally saline soil can usually be identified by the characteristic vegetation which grows there.

Salts usually accumulate on the soil surface when saline ground water rises to the surface. In dry weather, the water that rises to the surface evaporates more quickly. When it dries up, it leaves behind a white crust of salt. If there is not enough rainwater to wash out this salt, your field may become covered by the salt.

Good soil can become saline:
But good, fertile soil can also become saline. How does soil become saline? If you live in a coastal area where the land is lower than sea level, you know that sea water enters the land during high tides or cyclones. This salty sea water stays in the fields. Then, when it dries up, salt is left behind. When there are dams built in coastal areas, this problem can be prevented. Sea water can also seep underground into fields that are near the sea. It is difficult to stop sea water infiltrating the soil.

You may also have a salinity problem if you farm near an artificial salt lake or salt farm which is being used to produce salt. During the dry season, the water in salt lakes or farms dries and salt crusts form where the water used to be. Then, when there is heavy wind, the salt blows into the fields.

Over-irrigation:
The biggest cause of salinity is faulty irrigation. Unlike rainwater, the water from rivers, wells, or springs that you use for irrigation contains salts. If you irrigate too much the water sits in the field. Then, during the hot season, when it evaporates it leaves behind salt in your field. So you need to make sure that you do not irrigate your crops too much.

There is another problem related to irrigation. If you consistently over-irrigate your land and there is not enough drainage to let the extra water escape, or if you use irrigation canals which allow the water to seep out, too much water goes into the soil. That causes the ground water table to rise, bringing the water to the surface. Then the water evaporates at the surface and creates a suction effect, drawing the water and the salts up to the root zone of the plant.

Two ways to prevent salinity caused by over-irrigating are to use sprinkler or drip irrigation methods. These methods control the amount of water your plants get, but they may be expensive. The important thing is to irrigate carefully, and to try to give your plants just the right amount of water.

In most dry areas, underground water comes to the surface during the dry season by capillary action. Then it evaporates and leaves the salt at the surface. You can prevent this from happening by spreading mulch, such as paddy husks, dried leaves, manure, or compost on your field. You can also prevent the capillary action which makes the underground water come to the surface by ploughing or turning the soil regularly.

Spreading chemicals such as lime or gypsum on your soil is another way to reduce salinity. Lime and gypsum dissolve salt so that it is more easily washed away. Apply gypsum or lime to saline soil annually to improve the soil. When the plants are healthy, you can stop the applications.

Some plants, such as cotton, barley, sugar beet, and dates can tolerate salt. Others are moderately salt tolerant. But even salt tolerant plants are sensitive while they are germinating. So, if possible, you should grown the seedlings in a salt-free nursery bed and transplant them later.

Good soil makes for strong, healthy plants with high yields. Saline soil is a big problem for farmers, but there are ways to work with saline soil.

Acknowledgements

Theivendram Vigneswaran was Farm Manager at the Jaffna College Institute of Agriculture in Maruthanamadam, Sri Lanka.  He presently acts as a consultant with the Farm Radio Network in Toronto.

In the package 20 information poll, we asked participants about problems with soil salinity.  The responses received assisted in the preparation of this script.

Information Sources

Agriculture in the Tropics by C.C. Webster and P.N. Wilson.  Published by Longman Scientific and Technical, Longman House, Burnt Mill, Harlow, Essex CM20 2JE, ENGLAND.

Ecology and Management of Problem Soils in Asia.  FFTC Book Series No. 27, August 1984.  Published by Food and Fertilizer Technology Center for the Asian and Pacific Region, Agriculture Building, 14 Wen Chow Street, Taipei, TAIWAN.

“Halting the salt that kills crops,” by Femi Ajayi, Moyiga Nduru and Abdou Gningue, African Farmer, No. 4, July 1990, p. 22-27.  Published by The Hunger Project, Global Office, One Madison Avenue, New York, New York 10010, U.S.A.

Interview with James McGilligan, soil salinity expert working in Indore, M.P., INDIA.

 What We Learned, 1989, Jaffna College Institute of Agriculture, SRI LANKA.