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Salt in the soil
By Prof. R.B. Mapa, Dr. W.M.A.D.B.Wickramasinghe, D.N. Sirisena and K.M.A. Kendaragama
The tsunami on December 26 inundated large extents of cropland in the coastal areas of the country. With the action of the waves, tracts of land were physically damaged through soil erosion and also deposition of large amounts of sand and other debris. The irrigation and drainage channels were damaged. Agricultural machinery, implements and livestock were lost to the sea.

In addition, seawater intrusion led to the development of soil salinity, harming the present crop as well as making these lands unsuitable for cultivation in the near future. Salinity develops in the soil due to accumulation of soluble salts. As seawater contains considerable quantities of sodium bearing salts, its intrusion creates soil salinity. In addition Sodium ion causes the dispersion of soil particles, destroying their structure.

These factors need to be taken into consideration and an urgent programme to rehabilitate lands affected by the tsunami implemented immediately. To assist such land rehabilitation, the Soil Science Society of Sri Lanka has carried out a study in some affected areas.

For the first leg of the study, Ampara district in the eastern region where the paddy yield is high and the damage to the cropland was extensive was chosen. As most of the damaged paddy tracts were uniform, the Nintavur area was selected to assess the damage to the lowlands and Vinayagapurum in Thirukkovil where tomato, chillies, cowpea and brinjals are grown extensively to assess the damage to the highlands.

Soil salinity was assessed at different distances from the sea. Due to high rainfall and flooding immediately after the tsunami, there was a possibility of these salts leaking to greater depths. Therefore, soil salinity was assessed within the first 30 cm depth at 5, 15 and 30 cm on January 14, 2005, 18 days after the disaster. The rooting depth of most of the annual crops is also within the range of 30 cm. Standing water in the paddy fields, surface water remaining in the depressions in poorly drained spots in the highlands as well as water in wells was examined to obtain additional information.

Salinity in paddy fields
About 575 acres of paddy fields were affected in Nintavur where the soil type is alluvial (entisols). The rice variety cultivated in most fields was BG 94-1 and the crop was totally damaged due to salinity in these areas. As the crop was nearing maturity, grains have become empty.

The study results indicated that even after two weeks of the tsunami and the area experiencing heavy rains, salinity remained at higher values. As the seepage of water from paddy fields is poor due to the hard pan below the plough depth and as the drainage channels are blocked there is no way for the salts to be washed away. With continuing evaporation there is a tendency for the salinity levels to become more damaging.

Salinity in highlands
The Vinayagapurum village, where the highlands were examined consisted of about 460 acres of tomato, brinjals, chillies, maize and cowpea. These annuals as well as perennials such as banana and even palmyrah were damaged due to the waves and resultant salinity. The soil of this area is sandy regosols (entisols) and the water had drained away. Due to the heavy rains after the tsunami and the well-drained conditions, the salts have got washed off in these highlands. However, in areas where there was soil erosion due to the force of the waves, pools of stagnant water could be observed. The salinity levels of this stagnant water were high and thus highly damaging to many crops. In some of these areas where water had evaporated, patches of salt crust could be seen on the land surface.

Due to the high amount of Sodium, the soil structure is broken down (dispersed) and these lands will be susceptible to erosion. The well water in highlands also showed high salinity levels and the water table was near the soil surface. This well water cannot be used for any domestic or agricultural purposes. The shallow ground water table will contribute to an increase in salinity with time. As the evaporation rates are high in the yala season, the situation will be aggravated.

Rehabilitating paddy lands
Short term, medium term and long term strategies are proposed for the rehabilitation of these lands affected by salinity. The best short-term strategies for paddy lands are to drain them immediately before the salts get more concentrated due to evaporation. For this purpose the drainage channels should be cleaned and the sand and debris removed from the paddy fields. Salt-tolerant seed paddy varieties such as AT 353, AT 354 and AT 401 should also be collected immediately by the authorities -- even offering high prices to farmers who are already growing these -- to be distributed in the next season. Wherever clean water can be used to leach the salts, soil amendments such as gypsum could be used under the supervision of soil scientists to make the reclamation of land faster. Therefore, orders should be placed quickly for the gypsum requirement, for supplies to be available when needed.

As medium term measures (which may last about three months), farmers should be trained in special methods of cultivation that lead to the reduction of salinity. Here the salinity levels of the fields will have to be monitored closely. Efforts should also be made to produce more salt-tolerant varieties of seed paddy to last a few seasons until soil salinity decreases periodically.

As long term measures (longer than six months), farmers should be advised to clean and maintain drainage channels. Part of the water from the maha rains should be used to wash off the salts in the soil by adding gypsum, flooding the fields and ploughing them and draining them a few times to displace the sodium ions. This must be done under proper supervision.

Rehabilitating the highlands
The short-term measures for rehabilitating the highlands include removing sand and other debris from the land and improving drainage through the construction of drains to lower the water table. Wells should be emptied, cleaned and rehabilitated to ensure that salt water does not enter the subsoil. Once the wells are cleaned they could be used for domestic purposes and irrigation. Removing the excess water from eroded depressions should also be carried out as soon as possible. Programmes have to be initiated to distribute salt-tolerant crops for home gardens.

The medium term measures should be to educate the farmers about special agricultural practices to reduce salinity, providing agricultural implements and salt-tolerant varieties of crops and monitoring of the salinity levels by field officers. Conductivity meters for measuring salinity should be provided to agricultural extension officers in these areas of these areas.

As long-term strategies, farmers should be encouraged to maintain drainage channels effectively and to use the water from the maha rains to leach salts as much as possible.

For this purpose the soil structure has to be developed by applying organic matter for better drainage. A programme should be launched to make perennial plants available especially for home gardens.

General recommendations
Some recommendations for policy-makers:

Soil salinity should be viewed as a holistic problem affecting large extents of land rather than as an individual and isolated problem of farmers.
As paddy fields indicate high salinity levels and are poorly drained, those will be more difficult to reclaim. Therefore priority should be given to paddy lands in this exercise.
A detailed map of the affected agricultural land should be drawn up by the relevant authority.
The damage to land due to salinity should be assessed and rehabilitation undertaken at national level, with the participation of all stakeholders including farmers, soil scientists, extension officers and irrigation and drainage engineers.
Where individual allotments cannot be identified and damage is extensive, the state should rehabilitate the land as a national priority and resettle farmers.

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