Saline Soil Area Development in the Northeast: Geological approaches

32

“…The level of salinity in the salt affected soil at Khao Tao pineapple farm is getting higher after every crop. The foot hill of Khao Tao is covered with alkaline soil, transported from surrounding hills, my suggestion to solve this problem is to move the alkaline soil up to the top…”

“…A hazard has recently occurred in the Northeastern areas; rain water eroded down to the deeper soils and caused saline soil in many rice paddy fields. As I noticed such problems, the Land Development Department and other departments must integrate to solve this problem because this hazard did indeed occur. This level of salinity is serious and is very harmful to plants…”

The Royal woRds on 9Th augusT 2007

The Royal gRaCe oF hIs MaJesTy The KIng

The project employs three main strategies to sort out three different problems, which are: geological, agricultural and communal. The strategies include the study on the origins of the saline soil and causes of salt dispersion in the area; soil quality improvement methods; and selecting salt tolerant plants and rice strains for use in affected areas. The Saline Soil Development Learning Center has been set up at Tambon Haiyong, Phangkhon District, Sakon Nakhon Province. Here, the development model from the study is passed on to groups of farmers to further test and distribute the proposed solutions to the community to be applied in other affected areas.

On August 9th 2007, His Majesty the King granted an audience to the executives of the Department of Mineral Resources (DMR) to inform about the geological situation and present geological maps of Thailand. His Majesty the King gave an initiative to the DMR executives to conduct a geological research study in the Northeastern part of Thailand to determine the causes of the area’s saline soil and propose a proper solution to the problem present. In response to the King’s advice and initiative, the DMR has set up a project called “Saline Soil Area Development in the Northeast”. A small saline affected area located within Nam Un watershed, Sakon Nakhon Province has been selected as the first study area.

Cond

uctiv

ity (d

S/m

)

16

8

2

4

0.8

0.4

0.2 0.1

Salt Concentration (%

)

Salinity effects negligible

Only a few very tolerant cropsyield satisfactorily

Only tolerant crops yield satisfactorily

Yields of many crops are restricted

Yields of sensitive crops may be restricted

Strongly saline

Very strongly

saline

Moderately saline

Slightly saline

Non saline

54

Gravity lows delineate salt domesSalinity in the salt affected study area

The geological work that has been prepared is effective in creating a strong foundation for our continuing work due to its useful application in various exploration techniques including geological, geophysical and geochemical surveys on the saline soil project. The study of rice selection in particular has yielded great success. The success of our demonstration rice field, along with the participation of the people, has resulted in an Action Plan for the entire Haiyong Community.

In February 2008, the DMR launched the project called “Saline Soil Area Development in the Northeast” to study the causes and solve these soil salinity problems.The Integration of geological, agricultural and the communal strategies among participating offices and organizations are vital to the success of the project. The organizations involved are as follows: Office of Natural Resources and Environment, Sakon Nakhon Province; Rice Department; Department of Groundwater Resources; Pimai Salt Co., Ltd.; National Science and Technology Development Agency (NSTDA); Land Development Department, etc.

What to Do With Saline Soils?

Many provinces in the Northeastern part of Thailand (Isan) have been affected by saline soils which are caused mainly by dissolved sodium chloride from deep seated rock salt. During every dry season salt is interspersed on the lowland ground surface and it is leached away in the rainy season. The soil salinity has rapidly dispersed and has lowered the quality of life for many people; causing many economical, social and environmental problems.

Saline soils are soils containing high concentration of soluble salts which obstruct the growth of plants. Excessive salt damages plants by disrupting their intake of water and interfering with the absorption of nutrients. The table below shows the 5 classes of generally recognized saline soils and the effect on crops.

What Are Saline Soils?

Udon Thani

Ubon Ratchathani

Si Sa KetSurinBuri RamNakhon Ratchasima

Amnat Charoen

Sakon NakhonNakhon Phanom

Khon KaenKalasin

ChaiyaphumMaha Sarakham

Roi EtYasothon

Strongly Saline

Moderately Saline

Khorat Basin

Sakon Nakhon Basin

Non-saline terrain, 75.6 Million Rais

stronglysaline terrain,

1.4 Million Rais

moderatelysaline terrain,

5.7 Million Rais

slightly saline terrain, 23.3 Million Rais

Saline terrain, 30.4 Million Rais

76

Saline soil is caused naturally by rock salts that are dissolved by the groundwater and dispersed in the lowland where the groundwater table is very shallow. One serious, but avoidable, cause of the saline soil crisis is deforestation. The forest stabilizes groundwater table and simultaneously humidifies the atmosphere by absorbing groundwater via the roots and evaporating it through the leaves. Without the forest, groundwater table will rise up close to the ground surface and the air will be dry. These conditions are suitable for saline soil occurrences.

The strongly and moderately saline terrains covering fifteen provinces of Isan are located over the two sedimentary basins of the Khorat plateau

There are fifteen provinces affected by the salinity as follows: Udon Thani, Sakon Nakhon, Nakhon Phanom, Khon Kaen, Kalasin, Chaiyaphum, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Nakhon Ratchasima, Buri Ram, Surin, Si Sa Ket, and Ubon Ratchathani.

1. Strongly saline terrain

covers 1.4 million Rais of salt surface ground.2. Moderately saline terrain

covers 5.7 million Rais of scattered salt surface ground. 3. Slightly saline terrain

covers 23.3 million Rais of some scattered salt surfaced ground

The Khorat Plateau covers one third of the country. Twenty nine percent of the Northeastern part, about 30.4 million Rais*, is mapped as saline soil terrains with 3 degrees of salinity.

(*1 Rai covers an area of 40x40 square meters)

The Saline Affected Areas

Salt dome

Capillary zone

Groundwater table Fractures

Salt affected terrain

Capillary zone

Salt dome

Groundwater table rises up

Fault Fault

Salt dome

Humid air Dry air Deforest

Forest

Rock salt formation Younger formation

Older formations

Groundwater table

98

After the groundwater dissolves the salt domes, the catalyst to the saline soil crisis is the capillary force which pulls the brine up, against the gravity, to the surface. At this point, pure water evaporates from the brine and only salt is left behind. This process happens continuously under dry weather conditions where the groundwater table is shallower than 4 feet and the top soil is sandy.

The cause, the shortcuts and the catalyst The northeastern saline soil is caused mostly by rock salt being dissolved and dispersed by groundwater. However, the saline soil would not have spread widely over the plateau without the necessary shortcuts and catalyst. The salt domes act as shortcuts allowing the source of the salt to move closer to the surface, while the faults act as pathways for upward movement of the saline groundwater.

Under the Khorat Plateau lay various clastic sedimentary rocks of the Khorat group including conglomerate, sandstone, siltstone, shale and mudstone. Since the Mesozoic Era (251-65 million years ago), these sediments have been continuously deposited into a continental basin under an arid to semi-arid climate. At the end of the Era, after the seawater transgression dried out by the aridity, rock salt beds hundreds of meters thick were left behind. The rock salt was finally covered with very fine grained sediments transported by wind and water. The uplifting of the Khorat Plateau caused deformations and fractures in the rock sequence. Under great load pressure, the rigid rock salt behaves as a plastic body and flows upward through weak zones in the upper rock units to form salt domes. The fractured cap rocks can easily collapse when the top of the salt domes are leached by groundwater. Nowadays, many reservoirs spread throughout the Khorat plateau indicate the shallow buried salt domes.

The Khorat Plateau and the Hidden Gigantic Rock Salt

1110

The Geological Solutions on the Saline Soil ProblemsBentonite is a combination of clay minerals altered from igneous rocks or

volcanic tuff, e.g. montmorillonite, beidellite, nontronite, saponite and hectorite. When wet, bentonite absorbs water and forms an impermeable film which inactivates the capillary force. Bentonite deposits in the northeastern are mostly found in mud seepages in some provinces, e .g. Chaiyaphum and Sakon Nakhon Provinces.

The clay of Nawa is a weathering product of mudstone, claystone and shale of the Nawa rock member which is sitting on top of the rock salt beds. It composes of kaolinite, montmorillonite and quartz. Nawa clay can prevent the leakage of plant nutrients from the soil by absorbing water along with essential nutrients into its molecule’s stacked layers. Nawa clay is found in undulating terrains in some provinces, e.g. Sakon Nakhon and Khon Kaen Provinces.

Most of the clays found in river banks and in alluvial planes in the farm vicinity are satisfactory for soil structure improvement.

Typical Nawa clay at Nawa District, Nakhon Phanom Province

The reddish brown Nawa clay is found laying weathered and eroded under the lateritic layer.

The DMR has acted in response to the King’s advice and initiative to help people in saline soil affected area by cooperating with participatory offices and organizations to study on the soil quality improvement. Many solutions have been derived from the intensive study. The solutions are as follows: the use of salt leaching technique, the use of organic fertilizer, and the selection of salt tolerant plants and rice types for the area.

The geological investigation by the DMR indicated that the saline soil is caused by the leakage of saline groundwater. One good solution to this problem is the salt leaching technique. However, a better solution is to avoid the catalyst of the crisis by humidify the soil with agricultural materials, e.g. rice-husk, rice-straw and cover crops.

Further geological study has also identified a method to enhance the efficiency of saline soil protection by using geological materials found in the vicinity i.e., bentonite for saline groundwater trapping and the clay of Nawa rock unit for soil structure improvement.

Bentonite deposits are mostly found in mud seepages

1312

Six Steps to Improve the Salt Affected Areas

1. POND Prepare a pond to collect saline water from the salt leaching

process. This brackish water is useful for some fish farming, e.g. Nile tilapia and

Mozambique tilapia.

2. SALT LEACH Leach out the salt from the saline soil by flooding the rice

field with water fifteen centimeters high. Keep the field flooded for a few days.

Deliver the water to the prepared pond. Repeat the process 2 - 3 times.

3. CLAY FILL Fill up the rice field with the clay of the Nawa formation and

surrounding areas. To improve the soil structure, use approximately 10 tons of clay

per Rai.

4. BENTONITE SEAL Trap the saline groundwater with an impermeable

film of bentonite (if available). Use approximately 1 ton of bentonite per Rai.

5. NUTRIENT ADD Improve plant nutrients in the soil with natural fertilizer,

organic fertilizer or manure.

6. SALT TOLERANCE PLANT Select saline tolerant plants such as Khao

Dawk Mali 105 or RD6.

* Steps 3-5 can be applied at the same time and then plough together.

The results returned from the integrated study of the DMR and alliance indicated that saline soil in the northeastern is caused by deep seated gigantic rock salt being dissolved by groundwater. It is then dispersed to the top soil by seeping through the voids between sediment particles, which is most likely to happen in dry sandy soil. The most straightforward way of improving saline soil would be to leach out the salt and prevent its return. In addition, in order to yield better crops, some integration of agricultural techniques has been proposed.

Salty water is delivered to the prepared pond for tilapia farming

Learning Center

55 Km. to Sakon Nakhon

3026

1514

The Steps Forward

Uncle Khruea Suwanchai-rob and the map to his learning center

The lessons learned from this project have been applied in other salt

affected areas in the northeastern and transferred to related academic hubs

whose aims are to:-

• Distribute the knowledge

• Apply in other affected areas

• Select volunteer farmers to build up administrative farms and

learning centers.

The lessons learned have been transferred to academicians and farmers.

The success of the project “Saline Soil Area Development in the Northeast” depends greatly on the royal grace, the people participation and the integration among participatory offices and organizations. The studies of saline soil problems have resulted in effective geological approaches to lower the salinity of the soil and protect the land from increasing salinity, as well as saline tolerant plants and an action plan for the Haiyong Community. These satisfactory results have led to the improvement of soil quality by six steps and the opening of the Saline soil develop-ment learning Center

At the learning center, the development model from the study is passed on to groups of farmers to further experiment and share the results among the community to be applied in all other saline soil affected areas. The Demonstration Center for Knowledge Distribution directed by head farmer Khruea Suwanchai-rob is the experimental farm located at Tambon Haiyong, Phangkhon District, Sakon Nakhon Province.

The Department of Mineral Resources manages geological issues and geological resources

through people's participation for the benefits and happiness of the whole society.

Published in 2015 Division of Mineral Resources Conservation and ManagementDepartment of Mineral Resources (DMR)Ministry of Natural Resources and Environment (MONRE)75/10 Rama VI Road, Ratchathewi, Bangkok 10400www.dmr.go.th