Problem Soils: Managing Saline Soils
[addw2p name=”problemSoils”]
Kranji
Saline soils occur by the sea or around river mouths and are constantly inundated by sea or brackish water. Consequently, they have a young A/C profile with conductivity commonly above 10,000 µmhos cm-1. In potential acid sulfate soils such as Bakau series, may contain high water soluble sulfate exceeding 0.35%. Saline soils generally occur in low rainfall region in Malaysia.
Our plantation tree crops are not salt tolerant and hence cannot be grown on saline soils before ameliorations. Despite this, a number of large plantation companies in Malaysia, such as K.L. Kepong Bhd., Sime Darby Bhd. and Golden Hope Plantation Bhd., have successfully grown oil palms on it. However, before reclamation work proceeds, we have to ensure that at least the following conditions prevail at the site.
- materials for bunding are available,
- if (a) is unavailable, then the “n” value of the soils should be less than 0.7
- most of the land boundary should not be erosional surface,
- the land should preferably be higher than the sea or river level at low tides,
- rainfalls should be sufficient (> 1700 mm yr-1) to allow flushing and leaching of salts,
- land area must be sufficiently large to dilute the cost of reclamation and maintenance to economic level
Preventing further intrusion of sea or brackish water of more than 1000 µmhos cm-1 into the land is central to reclamation of saline soils. This is accomplished by construction a band around the periphery of the land. The bund should be at least 3 feet above the highest tide level.
Consideration must be given to the river and its tributaries in the land in deciding the course of the bund.
Upon completion of bund construction, a drainage network comprising main and collection drains must be laid down to reduce the water table and allow for subsequent flushing of the drains. There must be sufficient watergates and water pumps to remove the water trapped in the land. The periodic flushings usually continue for two to four years before the conductivity drops below 2000 µmhos cm-1 within the top 45 cm to allow successful planting of oil palms.
Once the above is achieved, field drains are then constructed to lower the water table to between 50 to 70 cm from the soil surface. Planting of oil palms and other cultural practices resemble those of coastal soils. However, boron application is generally unnecessary.
Bund maintenance to prevent seepage and leakage and sound water management are necessary to ensure successful reclamation of saline soils for oil palms. An example of yield profile of oil palms on saline soils with mean annual rainfalls of 18.22 mm is shown in Figure 5. The mean FFB yields were low due to two periods of distinct dry season per year although occasionally they may exceed 24 t ha-1 yr-1.
