Soil Profiles: Bungor
Bungor Series
The Bungor Series is a member of the Bungor Family which is a fine, kaolinitic, isohyperthermic, red-yellow Tipik Lutualemkuts. It typifies the family and is developed over mixed sedimentary rocks. These soils are characterized by dark greyish brown A horizons with fine sandy loam textures and deep B horizons having brownish yellow to yellowish brown colours and fine sandy clay textures. Consistence is friable and becomes firmer with depth. The structures are weak to moderate medium and fine subangular blocky. At depths below 75 cm few medium to coarse distinct red mottles may appear. At depths below 150 cm the colours become paler. This soils is developed over interbedded sandstones and shales or sandy shales. These soils have a kandic horizon and must have a CECclay of less than 16 cmol (+) kg–1 clay in all subhorizons between 25 to 100 cm depth. No significant clay decrease to 100 cm depth is permissible.
Type Location
The Bungor Series was first established on the western part of lower Sungei Lepar Valley in east Pahang by Libby (1964) during the Reconnaissance Soil Survey of Lepar Valley, Pahang. The above pedon was described on a 12° slope in undulating terrain near the village of Sri Jaya at the 37th milestone Kuantan- Temerloh Road. Location: Topographic Sheet 4259, 3°40’20” N, 102°52’40” E (Grid Reference 4259 – 426060 m).
Range in Characteristics
Soils of the Bungor Series show very little variation in the areas mapped to-date. They have colours which range from strong brown, brownish yellow and yellowish brown (7.5YR5/6; 5/8; 10YR5/6, 5/8, 6/6, 6/8). Rarely the colours may be reddish yellow (7.5YR6/6, 6/8). Textures range from fine sandy loam to fine sandy clay loam to clay. Clay contents seldom exceed 50% and fine sand always dominates the coarse sand which seldom exceeds 20%. Structures are weak to moderate medium and fine subangular blocky and consistence friable to firm with depth. Red mottles often appear at depths below 75 cm and increase with depth. The depth of the soil though often deep may sometimes be shallow on steep slopes as they grade into the Kuala Brang and Kuah Series. Some soils of the Bungor Series have a thin band of nodular petroplinthite but the band cannot exceed 25 cm in thickness. As defined here soils of the Bungor Series must have a CECclay of less than 16 cmol (+) kg–1 clay in all subhorizons between 25 to 100 cm depth.
Competing Soils and Their Differences
Soils of the Bungor Series are very similar to soils of the Serdang, Batang Merbau, Munchong Series and Jerangau Series. Both the Munchong and Jerangau Series may have similar colours to the Bungor Series but are heavier textured and have oxic horizons. The distinction between the Bungor Series and the Batang Merbau and Serdang Series is difficult. The Batang Merbau Series has a sand fraction dominated by medium sand while the Bungor Series is dominated by fine sand. The Bungor Series in the field does not show up any coarse sand and even the fine sand is so rounded that it is often not felt. The Serdang Series has fine sandy clay loam textures. The Batang Merbau Series also is reported to have mica flakes throughout the profile as it is developed over mica schists. Some of the Durian Series mapped in the past also may have 7.5YR hues but these have much siltier textures, redder colours at shallow depths, shallower profiles and very firm consistence. The Kuala Brang Series which has many features similar to the Bungor Series is a moderately deep equivalent of the Bungor Series and the saprolite is encountered within 100 cm. Soils of the Bungor Series can be easily mistaken for the Bedup Series (Sarawak) and Kumansi Series/deep (Sabah) or Merit Series (Sarawak) but these soils have a CECclay of more than 16 cmol (+) kg–1 clay in some subhorizon between 25 to 100 cm depth.
Setting
Soils of the Bungor Series are developed over interbedded sandstones and shales or sandy shales. They have been mapped over a wide range of terrain ranging from gently undulating to steep. The commonest range is undulating to hilly.
Principal Associated Soils
Soils of the Bungor Series have often been mapped in association with soils of the Serdang and Munchong Series. The Serdang Series has fine sandy clay loam textures, is more friable and weaker structured than the Bungor Series. The Munchong Series on the other hand is heavy clay textured, more friable and has an oxic horizon. As defined here soils of the Bungor Series may now be associated with soils of the Bedup, Kumansi/deep and Merit Series from which it can be differentiated using the CECclay values.
Drainage and Permeability
Soils of the Bungor Series are well drained and have a good permeability.
Use and Vegetation
Soils of the Bungor Series are commonly planted with a variety of crops including rubber, oil palm, fruit trees, cocoa. Some of these areas are still under primary forest vegetation.
Distribution and Extent
The Bungor Series is fairly well distributed in Peninsular Malaysia. It has been mapped in Perak, Selangor, Negeri Sembilan, Johore, Malacca, Pahang, Terengganu and Kelantan. Their extent is however not known.
Series Established
The soil was established during the Reconnaissance Soil Survey of the Lepar Valley, Northeast Pahang (Libby 1964). The source of name is the village of Paya Bungor on the Kuala Lumpur-Kuantan road.
Remarks on Classification
Soils of the Bungor Series are classified here according to the Malaysian Soil Taxonomy – Second Approximation (Paramananthan 1998) as a member of the fine, kaolinitic, isohyperthermic, red-yellow family of the Tipik Lutualemkuts. They have a deep kandic horizon which has a low base status and in which the clay content does not decrease significantly within 1.0 m of the surface. The CECclay is less than 16 cmol (+) kg–1 clay in all horizons between 25 to 100 cm depth. Soils of the Bungor Series would be classified as Typic Kandiudults in the Keys to Soil Taxonomy – Eighth Edition (Soil Survey Staff 1998). In the FAO/ UNESCO Soil Map of the World – Revised Legend (FAO 1990) they will be classified as Haplic Nitisols.
Suitability for Agriculture
These soils are some of the better sedentary soils found in Peninsular Malaysia. Terrain should be the major limiting factor in these soils. Their fertility status like most soils in this country is low.
Soil Profiles: Bekenu
Bekenu Series
The Bekenu Series is a member of the Bekenu Family which is fine loamy, siliceous, isohyperthermic, red-yellow to yellow Tipik Tualemkuts. It typifies the family and is developed over mixed sedimentary rocks. Soils of the Bekenu Series are redefined here as being characterized by their deep, well drained profiles with brownish yellow to yellow subsoil colours dominating the subsoil. These soils have an argillic horizon with fine sandy clay loam textures and a ECECclay of less than 24 cmol (+) kg–1 clay in all subhorizons between 25 to 100 cm depth. Structures are weak medium to coarse subangular blocky and consistence is friable. Patchy clayskins occur on ped faces.
Type Location
Soils of the Bekenu Series were first described by Andriesse (1972) during the reconnaissance soil survey of West Sarawak. The above pedon was described by Lim Chin Pang for the CLAMATROPS Tour II organised by the Malaysian Society of Soil Science in 1977 at the 24th milestone Bau-Lundu Road in West Sarawak. The pedon was located on rolling (12–24% or 6–12° slopes) terrain at an elevation of 50 metres (150 feet). The vegetation was logged lowland Dipterocarp Forest. Location: Topographic Sheet 1/109/8, 1°33’20” N, 109°54’00” E (Grid Reference 1/109/8 – 892715 m).
Range in Characteristics
In the past in Sarawak, soils of the Bekenu Series were mapped as Red-Yellow Podzolic soils which can either have a cambic, kandic or argillic horizon with hues of 10YR or 2.5Y with any CECclay value. They are redefined here as soils having only an argillic horizon with red-yellow to yellow colour class and a CECclay of less than 24 cmol in all subhorizons between 25 cm to 100 cm depth. Little is known about the range in characteristics of the Bekenu Series. They generally occur on rolling, hilly to steep terrain. On the steeper terrain the profiles become moderately deep and are no longer the Bekenu Series. Textures in this soil are uniformly fine sandy clay loam and colours are brownish yellow, yellow to olive yellow (10YR6/6–6/8, 7/6–7/8, 8/6–8/8; 2.5Y6/6–6/8, 7/6–7/8, 8/6–8/8). Structure are generally weak medium to coarse subangular blocky and consistence friable. Patchy clayskins are often present. Only the deep soils are retained as belonging to the Bekenu Series in this redefinition. CECclay values are higher than 16 but less than 24 cmol (+) kg–1 clay. In some profiles a few subhorizons may have a CECclay of less than 16 cmol in the 25 to 100 cm depth.
Competing Soils and Their Differences
Soils of the Bekenu Series can easily be confused with other soils developed over mixed sedimentary rocks. Where the clay contents approach 35% they can be confused with soils of the Merit or Bedup Series in Sarawak, the Bungor Series in Peninsular Malaysia and the Kumansi/deep Series in Sabah but all of these soils have more than 35% clay while the Bekenu Series has less. Where the clay content is close to 18% soils of the Bekenu Series can be confused with soils of the Nyalau Series in Sarawak, the Malau Series in Peninsular Malaysia and Kapilit Series in Sabah all of which have less than 18% clay. Other deep soils with fine sandy clay loam textures include the Tukau Series over non-accreting alluvium and the Biawak Series with 2.5Y Hues throughout over metamorphosed sedimentary rocks in Sarawak, the Serdang Series in Peninsular Malaysia and the Tanjong Lipat Series in Sabah. In the proposed redefinition here, the Serdang Series has a kandic horizon (CECclay < 16 cmol) while the Tanjong Lipat Series has an argillic horizon with an CECclay of more than 24 cmol. The Tukau Series like soils of the Rasau Series developed over non-accreting alluvia. The Biawak Series could possibly be correlated to the Bekenu Series yellow variant and this variant could then be deleted from the list of soil series. More data is required.
Setting
Soils of the Bekenu Series typically occur on rolling and hilly terrain (slopes of 12–38% or 6–20°) at elevations of less than 1,000 metres (3,300 feet).
Principal Associated Soils
In the lowlands, soils of the Bekenu Series to-date have been mapped in association with soils of the Nyalau and Merit Series. On the steeper slopes moderately deep and shallow equivalents have also been mapped. These soils are distinguished using the particle-size class and the diagnostic horizon.
Drainage and Permeability
Soils of the Bekenu Series are well drained soils with a good permeability.
Use and Vegetation
Soils of the Bekenu Series have been used extensively for agriculture. They have been used for shifting cultivation, rubber, oil palm and pepper. On the steeper slopes these soils are retained under forest.
Distribution and Extent
To-date soils of the Bekenu Series have only been mapped in Sarawak. The actual extent of these soils is not fully known.
Series Established
This soil was first established by Andriesse (1972) during the reconnaissance soil survey of West Sarawak. The source of name is not known.
Remarks on Classification
The Bekenu Series as redefined here is classified here according to the Malaysian Soil Taxonony – Second Approximation (Paramananthan 1998) as a member of the fine loamy, siliceous, isohyperthermic, red-yellow to yellow family of Tipik Tualemkuts over sedimentary rocks. They are classified here as soils that have a deep argillic horizon with a CECclay of less than 24 cmol (+) kg–1 clay in all subhorizons between 25 to 100 cm depth and with brownish yellow colours. In the Keys to Soil Taxonomy – Eighth Edition (Soil Survey Staff 1998) these soils would probably be Typic Paleudults because these soils have a deep argillic horizon. In the FAO/UNESCO Soil Map of the World – Revised Legend (FAO 1990) the Bekenu Series would probably be classified as Haplic Acrisols due to their CECclay values of less than 24 cmol and the low base saturation.
Suitability for Agriculture
The low fertility status and the terrain on which these soils occur are the main limiting factors for the use of these soils. With proper fertilisation and soil conservation measures a wide range of crops can be cultivated on these soils. These include oil palm, rubber, pepper, fruit trees and upland rice.
Soil Profiles: Apas
Apas Series
The Apas Series is a member of the Apas Family which is a very fine, oxidic, isohyperthermic, red Tipik Tempalemoks. It typifies this family and is developed over andesites. Soils of the Apas Series are characterized by their deep well drained heavy clay textured oxic horizons which have an ECEC of more than 1.5 cmol (+) kg–1 clay. These soils are red or yellowish red in colour in the subsoils. Structures are moderate to weak, fine, subangular blocky and consistence is friable.
Type Location
Soils of the Apas Series were first established by Paton (1963) during the reconnaissance soil survey of the Semporna Peninsula. The above pedon was described by Paramananthan (1997) for the Soil Familiarisation and Soil Management Tour 2/1997 Tawau-Semporna, Sabah. The pedon was located under oil palm on rolling terrain at an elevation of 150 m (450 feet) in Ladang Sungei Kawa along the Tawau-Quoin Hill road. Location: Topographic Sheet 4/118/9, 4°23’15” N, 118°01’50” E (Grid Reference 4/118/9 – 919843 m).
Range in Characteristics
Little is known about the range in characteristics of the Apas Series. The soils are almost always deep with colours ranging from yellowish red to red within 50 cm of the soil surface. Field textures are uniformly clayey with more than 60% clay. However poor dispersion sometimes gives high silt values in the analysis results. Structures are weak to moderate medium subangular blocky and consistence is friable. The ECEC must be more than 1.5 cmol (+) kg–1 clay. It must be pointed out that those soils mapped in the past as Apas Series with an ECEC of less than 1.5 cmol should be now reclassified as the Segamat Series.
Competing Soils and Their Differences
Many soils have the red colours similar to that of the Apas Series. Soils having both a red colour, heavy clay texture and an oxic horizon include soils such as the Segamat, Prang and Kampong Kalam Series. These soils have an ECEC of less than 1.5 cmol (+) kg–1 clay. Other red soils with an oxic horizon include the Tarat/deep, Sagu and Patang Series which all belong to the Apas Family. These soils have an ECEC of more than 1.5 cmol (+) kg–1 clay and are differentiated by the parent material from which they are formed. The Apas (moderately deep soil), Tarat and Jebong Series (moderately deep soil) are all developed over andesites and could possible be correlated to form just one soil series after more work is done. The Sagu Series is developed over limestone while the Patang Series over hornfels (metamorphic rocks).
Setting
Soils of the Apas Series typically occur on undulating, rolling to hilly terrain (4– 38% or 2–20° slopes) at elevation of less than 200 metres (< 660 feet).
Principal Associated Soils
The Apas Series has often been mapped together with other soils developed over fine grained intermediate and basic igneous rocks such as andesites and basalts. As redefined here soils of the Apas Series can be expected to be mapped in association with soils of the Segamat, Table Series and soils of the Kobovan and Beeston Series. In the existing maps the Apas Family included soils with an ECEC of more than and less than 1.5 cmol (+) kg–1 clay. The Apas Series as redefined here only includes soils with an ECEC of more than 1.5 cmol. Both the Kobovan and Beeston Series have an argillic/kandic horizon while the Table Series has brown colours.
Drainage and Permeability
Soils of the Apas Series are generally well to somewhat excessively drained with good permeability.
Use and Vegetation
Soils of the Apas Series have been planted with oil palm, rubber and cocoa but in some areas they remain under primary forest.
Distribution and Extent
The Apas Series has to-date been only mapped in the Sandakan and Tawau Residencies in Sabah. Their actual extent based on their redefinition here is not known but can be expected in areas mapped as Segamat in Peninsular Malaysia and as the Tarat Series in Sarawak.
Series Established
The Apas Series was established by Paton (1963) during the reconnaissance soil survey of the Semporna Peninsula. The source of name is the Apas River to the east of Tawau.
Remarks on Classification
The Apas Series as redefined here is classified according to the Malaysian Soil Taxonomy – Second Approximation (Paramananthan 1998) as a member of the very fine, oxidic, isohyperthermic, red family of Tipik Tempalemoks over fine grained intermediate and basic igneous rocks. They are classified here as soils having a deep, red oxic horizon which have heavy clay textures and an ECEC of more than 1.5 cmol (+) kg–1 clay. In the Keys to Soil Taxonomy – Eighth Edition (Soil Survey Staff 1998) this soil would probably be classified as a Typic Hapludox. In the FAO/UNESCO Soil Map of the World – Revised Legend (FAO 1990) the Apas Series would probably be classified as Haplic Ferralsols.
Suitability for Agriculture
The main limitation for agriculture in these soils is their generally low fertility status, high P fixation and their high permeability.
Soil Management: Soil Profiles
The soil profiles are taken from ‘Soils of Malaysia | Their Characteristics and Identification’ by Selliah Paramananthan from Param Agricultural Soil Surveys (M) Sdn. Bhd., A4-3 Jalan 17/13, Happy Mansion Block A, Section 17, 46400 Petaling Jaya, Selangor, Malaysia. To purchase this book, please click here.
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Problem Soils: Conclusions
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Proper understanding of soils and crops has allowed us to exploit marginal soils successfully in Malaysia. Upon corrections or alleviation of the soil constraints, the oil palm performances can generally match those on better soil types. More than one soil management approaches are usually required and these must be implemented correctly and interactively. Among others, good timing is also essential to ensure success.
It must be cautioned that cultivation of oil palms on marginal soils entails higher cost, difficult inputs, good managerial skill and exposes the planters to higher risk and poorer competitiveness. It is therefore advisable to regard planting on marginal soils as a last resort rather than an opportunity for development and business.
Problem Soils: Managing Sandy Soils (Quartzipsamments)
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Lintang
The extent of quartzipsomments in Malaysia has not been reported. However, they are known to occur extensively besides mining or ex-mining areas and flat river basins. Some of these soils are classified as Sg. Buloh, Subang, Nangka, Lintang and Jambu series. The major limitations of these soils mirror those of podzols except that perched water table does not exist.
The management procedures for oil palms on these sandy soils are similar to those on podzols except that scupper drains are not dugged. Our experience with plantings on these soils has been fortunate because they occur in high rainfall regions of Central Perak and Southern Kedah. Their yield performances are shown in Figure 7 also.
Problem Soils: Managing Podzols or Spodosols
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Buso
Podzols generally occur within BRIS (Beach Ridges Interspersed with Swales) soils although they have been found on moderate hills in East Malaysia. The total extent of these soils in Peninsular Malaysia alone has been estimated at 162,000 ha (Choo, 1991). Majority of these soils are used for tobacco, vegetables, cashew nut trees and star-fruit trees. Of late, some of these soils which occur in the plantations have been cultivated with oil palms.
The major constraints in Podzols are perched water table, low nutrient status and CEC and poor moisture retention capacity. Some podzols may not have perched water table and these soils resemble quartzipsamments, which are discussed later.
The obvious first priority is to remove the stagnant water on the soil surface. This is easily accomplished by digging scupper drains with lower depths breaking the hard spodic horizons. The intensity of drains is usually 1 in 8 palm rows although this varies with sites. The top width of the drain is 60 cm and the bottom width is 30 cm to allow for more gentle slope, therefore easier maintenance.
Upon surface drainage, the conditions reverted to the other extreme of likely severe moisture stress due to excessive drainage and low moisture retention capacity. Hence, water conservation practices similar to those described for lateritic soils earlier must be improved immediately. The EFB mulching rate should be increased to 60 to 80 t ha-1 yr-1 and this is continued for at least 5 years before a lower rate is adopted.
The poor nutrient status and retention capacity pose a dilemma of high total fertiliser input but low rate at each application. This is generally solved by using compound or mixture fertilisers supplemented with straight fertilisers. The total fertiliser applications may reach 7 to 9 rounds a year and this should minimise leaching losses. Despite the sandy soils with anticipated low P fixing capacity, high phosphate rock is still recommended to ensure good root development and activity. Very high rate of ground magnesium limestones (GML) is also necessary to build-up the soil Mg status and prevent Mg deficiency.
Good ground vegetation is also important in reducing the surface soil temperature, which helps to reduce soil water evaporation and improve microbiological activity. The leaf litter return also binds the soil particles for better structure and aggregation.
Our experiences with planting oil palms on Podzols with satisfactory rainfall or more than 2000 mm yr-1 has been encouraging as shown in Figure 7.
Problem Soils: Managing Shallow Lateritic Soils
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Jitra
Shallow lateritic soils such as Malacca and Gajah Mati series, and their associated soils occupy 0.6 million hectares in Peninsular Malaysia (Law and Selvadurai, 1968). Early experiences indicated that oil palms grown on shallow lateritic soils came into bearing two years later and three times less compared to deep soils (Tan and Thong, 1975; Pang et al., 1977). Increasing the fertiliser rates only partially alleviate the constraint and improve yield by –% (Tan, 1973). Productivity also seems to improve with palm age (Tayeb et al., 1991).
These results show that the main problems with shallow lateritic soils are low effective soil volume, poor nutrient status and water holding capacity. These detriments further hinder root development, which aggravates oil palm growth and production. It has to be mentioned that the types and compactness of the laterites also play a major role on the degree of severity of limitations to oil palms. For example, the less compact and subangular laterites of Jitra series pose only moderate limitation to oil palms compared to very serious limitation in Malacca series despite both being shallow lateritic soils.
The main approaches to obtain satisfactory oil palms on shallow lateritic soils are to improve soil fertility and implement soil and water management adroitly. Improvement in soil fertility is necessary to increase nutrient uptake per unit soil volume. Since most lateritic soils are well weathered with low CEC and high P fixing capacity, it is necessary to maintain high and balanced rates of manuring as well as frequent applications to the palms. It is also essential to apply very large quantity of phosphate rocks to ensure sufficient P for good rooting activity.
The primary aims of soil and water management here are to reduce run-off and soil erosion, and build-up organic matter in the soil. These are achieved by:
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maintain desirable ground vegetation such as legumes during immaturity to early maturity phase and light grasses and Nephrolepis biserrata in later years,
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Spread the pruned fronds as broadly as possible. In flat areas, L-shaped frond stacking should be carried out while in terraced areas, they should be staked on the terraced lips and between the palms along the terraces,
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terraces must have sufficient back-slope and regular stops along the terraces to trap soil and water,
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mulching with empty fruit bunches (EFB) if available
Irrigation should only be conducted if it is economically viable, easy to maintain and a ready source of water during the dry season is available as mentioned in Part I of this lecture notes.
It is also advisable to increase the planting density to 148 palms ha-1 and extend ablation by 3 to 6 months for maximum leaf area index and high better yields.
Proper implementation of above soil fertility, and soil and water managements had raised the oil palm. Yields on commercial scale as shown in Figure 6.
Problem Soils: Managing Saline Soils
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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.
Problem Soils: Managing Shallow Acid Sulfate Soils
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Sedu
Acid sulfate soils are estimated to cover an area of about 110,000 ha in Peninsular Malaysia with at least 20,000 ha under oil palms (Poon and Bloomfield, 1977). These soils are characterised by very low pH values (< 3.5) and the presence of yellowish jarosite (Kfe3 (So4)2 (OH)6) mottles (Shamshuddin and Auxtero, 1991).
The problems with acid sulfate soils are:-
- they tend to be waterlogged in their natural state and must be drained before cultivation, and
- draining beyond the pyrite layer will generate excessive acidity which is detrimental to palm growth.
The latter is due to the oxidation of pysite to form sulphuric acid as shown below:
This oxidation also causes breakdown of clay minerals which releases Al, Mn and K into the soil solutions (Shamshuddin and Auxtero, 1991). The drop in pH to below 3.0 is not uncommon and the oil palms will suffer hyperacidity symptoms and poor yields Toh and Poon (1982) further, classified acid sulfate soils into 3 categories based on oil palm performances. Their severe category has acid layer at 0 to 60 cm while current soil classification in Malaysia tag it at 0 to 50 cm for shallow acid sulfate soils, such as Linau and Sedu series.
Hew and Khoo (1970) found that liming was generally ineffective to control acidity in acid sulfate soils. Poon and Bloomfield (1977) then showed that by creating anaerobic conditions, the reaction in equation (1) will not proceed and thus, preventing the generation of acidity. Since inadequate drainage will give rise to flooded conditions which also adversely affect palm performance, a balance has to be struck between over and under drainage.
This balance is achieved through a network of field, collection and main drains similar to those found in peat swamp as described earlier but their objective differs. The prime requirement in the management of acid sulfate soils is that the water-table should be maintained above the pepsitic layer for as long as possible. This is again carried out using stops, weirs and watergates, their numbers are largely determined by the depth to pysiritic layer and slope of the land. Normally, the water-table is maintained between 45 to 60 cm from the soil surface, hence, the depth of field drains should not exceed 75 cm. Otherwise, there is a risk of accelerated oxidation of the pyritic layer during dry weather conditions (Poon, 1983).
Another important aspect in the management of shallow acid sulfate soils is to provide for periodic flushing of the drains to remove the accumulated toxic polyvalent ions such as Al3+ and the extremely acidic water (Poon, 1983). Therefore, during the wet season, all the water retention blocks and watergates are opened to allow flushing. One to two flushing during the wet season are usually adequate. Before the end of the wet season, the blocks and watergates are again closed to allow fresh water to build up to the required level.
The other aspects of management of acid sulfate soils are similar to those of coastal non-acid sulfate soils. The success in using water control to manage oil palms on shallow acid sulfate soils is best illustrated by Figure 4.
