Land Development : A Fundamental of Sustainable Agriculture


Reactivation Theory

His Majesty the King has made annual trips to the southern part of Thailand and found out that southern people were facing the problem of "peat swamp" from the flooding in the rainy season. Drainage of water from peat swamp resulted in acid sulfate soil which again is not suitable for agriculture.

Peat soil is generally composed of organic materials on the top soil whereas the sup soil (more than 1-2 meters deep) is mainly sulfate in component (pyrite : FeS2 ). Wherever water is drained out from the soil surface, pyrite reacts with oxygen in the air to form sulfuric acid making more acid sulfate soil.

Trying to overcome this complication His Majesty has set up a research project on "Reactivation of acid sulfate soil". He suggested a technique of repeatedly switching the soil from soak wet to dry and make it extremely acid. Then use 2 main treatments to revitalize this extremely acid soil for cultivation. The treatments are as follows:

1.Control the level of underground water
By keeping the water above the pyrite muddy soil, the pyrite itself is unable to react with oxygen in the air (oxidation of pyrite is prevented) by following the procedure: 1.1 set up the draining system in the whole area
1.2 drain the surface water to wash out acidity
1.3 keep the water level in the draining canal not lower than 1 meter from the top soil all year round Draining must be coupled with good irrigation system to make it effective. Draining system itself will prevent the flooding and drain the excess water while irrigation system would wash out acidity and keep the underground water at the specific level.

2. Three procedures to revitalize acid sulfate soil depending on the type of soil 2.1 washing out acidity by
2.1.1 flood in and drain water out 2-3 times
2.1.2 let the water stay on for 1-2 weeks before draining
2.1.3 do the washing during the rainy season to save irrigation water
2.1.4 washing out acidity must be done continuously for long term purpose,
once or twice is not enough 2.1.5 this is the easiest way but use a lot of water both for washing and maintain
the level of underground water Soil pH would be higher while the toxic elements like ferrous and aluminum will be diluted to the suitable level of cultivation if nitrogen and phosphate fertilizers are added to the soil.
2.2 Adding lime to soil surface
2.2.1 use local available lime, i.e., Marl in central region or lime dust in the south,
and distribute the all over the soil surface (1-4 tons /rai) and plough 2.2.2 the amount of lime used depending on the level of soil acidity

2.3 Adding lime couple with washing out acidity and control the level of underground water. It should be performed in steps as follows:
2.3.1 lime is added (1-2 tons/rai)to activate water effectively
2.3.2 plough the soil over
2.3.3 washing out acidity with water
2.3.4 keep the underground water above muddy soil to prevent oxidation of pyrite

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