Acid sulfate, Beach Ridges Interspersed with Swales (BRIS), tin-tailings, peat and steep land soils are problematic soils with severe limitations for crop cultivation in Malaysia. Agronomic challenges, particularly low cation exchange capacity (CEC), high acidity, intensely leached, low nutrient status and low water holding capacity are the main problems encountered by farmers in managing these groups of marginal soils for productive agriculture. These agronomic challenges need to be addressed to enhance crop production with efficient resource utilization and improvement in soil fertility. Thus, this paper highlights some of the agronomic practices and soil fertility management utilized in Malaysia for managing these marginal soils sustainably without reducing soil and crop productivity not only to meet the current and future food demand but also to simultaneously improve the livelihood of farmers and increase revenue for crop plantations. Some of the established methods in managing problematic soils in Malaysia include the use of either organic or inorganic soil amendments and their co-application, whereas examples of agronomic practices comprised of the improved drainage system, fertilization schedules, crop selection and an upgraded irrigation system. It is hoped that the details from the agronomic approaches and soil fertility management shared will provide insights and an in-depth understanding of marginal soil management in Malaysia.
Keywords: problematic soils, crop production, reclaimed, soil fertility management, soil amendments
Malaysia has a total land area of approximately 33 million hectares, out of which 13.2 million hectares are located in West Malaysia and East Malaysia at 19.8 million hectares. Based on the land cover statistics by the Department of Agriculture Malaysia, about 53% (7 million hectares) of the total land area in West Malaysia (Peninsular) is suitable for agriculture (DOA, 2020), whereas land area unsuitable for agriculture is reported to be higher in East Malaysia at 15 million hectares. These soils are usually referred to as problematic soils and consist of several marginal soils namely deep peat (> 2m), tin-tailings, BRIS, acid sulfate, steep land and saline soils.
Malaysia is an agriculture-driven economy where most of its arable land is utilized for agriculture. Hence, the need to ensure food security and to meet current and future food demand had resulted in the encroachment of these marginal soils for cropping. This paper examines some of the management aspects of the major problem soils and their prospects for agricultural development.
AVAILABILITY AND CONSTRAINTS
BRIS and tin-tailing soils
BRIS soils are a complex of soils typically referred to as the alternating parallel sandy beach ridges and low depressional areas which are commonly developed on the sandy coastal ridges of Malaysia. BRIS soils occur as a narrow belt varying in width between 0.2 km and 8 km from the coastline and they are mostly Entisols and Spodosols. Compared with BRIS soils, tin-tailings are heterogeneous soils resulting from waste deposits from mining activities. However, tin-tailing soils have no profile development and are classified as Entisols (Shamshuddin et al., 2021).
The properties of BRIS and tin-tailing soils are rather similar (Table 1) because their soil texture is sand though tin-tailing soils have a wider range of pH. This could be attributed to the original tin mining areas which consisted mostly of peat, acid sulfate or underlaying materials of limestone. Due to the sand texture, BRIS and tin-tailing soils are infertile with low water-holding capacity and are subject to high nutrient leaching (Sittaphanit et al. 2009). Also, these marginal soils are subjected to high soil temperatures, which could reach more than 40 oC at the surface, thus inhibiting germination and retarding crop growth. Moreover, during the prolonged dry season (June to September), the conditions of these soils are similar to that of the semi-arid regions. Conversely, during the wet season, some of the BRIS soils are completely inundated. Therefore, an effective infrastructural drainage system is crucial in flood-prone areas. In addition, improvement in agricultural technology with emphasis on sandy soil management is required to ensure productive agriculture.
Peatland covers approximately 2.6 million hectares in Malaysia accounting for 8% of the total land area in the country. Presently, about 1.08 million hectares or 40.2% of the peatland in the country have been developed for oil palm, pineapple, sago, rubber, coconut, and mixed horticulture (Choo et al., 2020), whereas the remaining areas are under forest cover. However, only premium cash crop commodities, particularly oil palm and pineapple are largely cultivated on peat soils. Fruit crops such as papaya, banana, coconut, ciku, rambutan, and durian are planted on peat soils under mixed cropping systems. These fruit crops account for 16% of the total fruit agriculture area in Malaysia. Sago, an aquatic plant adapts well to peat soils with minimal agronomic problems leading to improved livelihood and economic returns. Likewise, non-aquatic plants such as pineapple adapt well to low acid and low fertility conditions. Rubber cultivation has been attempted but the acreage decreased as numerous problems occurred (Bachik et al., 1984).
Generally, the selection of crops for cultivation on peat soils is limited by low nutrient content, high acidity, high water table, and poor root anchorage. However, peatland is suitable for a narrow range of crops, particularly those with shallow rooting and fibrous root systems. Root crops such as cassava and sweet potato have been found to adapt well to drained peat soils. The loose nature of peat soil helps tuber development, but these root crops are sensitive to flooding or too much drainage. The major limitation of the commercial production of these crops is the difficulty in developing mechanized field production systems, particularly for harvesting. Vegetable production (e.g., okra, french bean, cabbage, cucumber, tomato, and leafy vegetables) on peatland through intercropping is both agronomically and economically beneficial. However, the cultivation of vegetables in open field systems is subjected to damage due to heavy rainfall, excessive solar radiation, high incidence of diseases and weeds, and high leaching of applied fertilizers. Nevertheless, agronomic challenges, particularly nutrient deficiency, high acidity, irreversible drying, low bearing capacity, and water logging conditions, are the main problems encountered by farmers in managing peat soils in Malaysia (Ahmed et al., 2013).
Peatlands need to be drained for agricultural development. Once a peat soil is drained, the upper soil layer oxidizes and slowly decomposes resulting in peat shrinkage and surface subsidence. Initial subsidence is caused by loss of buoyancy and consolidation during which the rate of subsidence may be extreme (50 cm), whereas subsequent subsidence is caused by oxidation and shrinkage where the rate of subsidence stabilizes between two and five cm yearly depending on the current water management regime (Joosten et al., 2012; Safiyanu, 2018). Generally, the construction and maintenance of drains are fairly expensive. This is because the peatland drainage system is designed not only to provide proper water table control and to minimize soil subsidence but also as a flood mitigation control measure. However, excessive drainage leads to desiccation in the upper soil layer because of the loss of water volume resulting in the peat becoming water repellent. Over drainage is a common problem in peatlands because water naturally moves rapidly in the upper soil layer during the draining process. Also, reclaimed peat areas are susceptible to burning which could seriously damage crops and emit greenhouse gas, particularly carbon dioxide and toxic gaseous compounds that are carcinogenic (e.g., aromatic hydrocarbons and benzene).
Malaysian peat soils have a high void ratio and porosity due to the large, hollow, and porous organic fibers in peat soils. The high void ratio and porosity lead to high hydraulic conductivity and high permeability in peat soils. The bulk density of peat soils is typically low and ranges from 0.05 to 0.12 g/cm3 in the uppermost 30 cm layer. The woody nature and low bulk density of the soil restrict the use of machinery and top-heavy tree crops such as oil palm and papaya tend to lodge and topple over due to poor root anchorage in peat soils (Mohammad et al., 2007).
The chemical properties of peat soils vary with location and are dependent on the nature of the mineral substratum and the thickness of the organic layer. Ash content in peat soils is less than 10%, indicating a high amount of organic matter loss during ignition. Peat soils are also acidic with pHw (pH in water) values ranging between 3.0 and 4.5. These organic soils are also known to be deficient in micronutrients particularly Cu, Zn, Fe, and B. This is because Cu, Zn, Fe, and B occur mostly in non-extractable form due to the formation of stable complexes between these metal ions and the solid phase of organic matter to form strong humic-metal chelates (Abat et al., 2012). Preliminary studies by MARDI also indicated that there is fairly high microelement adsorption in peat soil (Ismail et al., 2007).
Acid sulfate soils are only found along the coastal areas of the country. Under natural conditions, acid sulfate soils are subjected to tidal influence and are frequently inundated by seawater. However, acid sulfate soils must first be reclaimed before they can be used for agriculture. A considerable acreage of acid sulfate and potential acid sulfate soils in Malaysia contains substantial quantities of pyrite minerals (FeS2). The limitations of acid sulfate soils with underlying pyrite minerals for agriculture in Malaysia are well-documented. These include very low pH, Al toxicity, nutrient deficiency, susceptibility to flooding and the adverse effect of excessive drainage (Shamshuddin et al., 2017).
In the past, large areas of acid sulfate soils on the West Coast of Peninsular Malaysia were over-drained, which lowered the water table below the pyrite accumulation zone. This process slowly oxidizes the pyrite resulting in very acidic soil (pH 2.6 to 3.4). The distribution of pyrite in soils is usually sporadic, both vertically and horizontally. Thus, acid sulfate soil often occurs as patches in association with other fertile soils. This poses practical problems during land reclamation, where some areas are unavoidably subjected to excessive draining during the draining process (Padmini et al., 2022).
One of the major constraints associated with soils in sloping areas is erodibility. The topography and intensity of tropical rainfall led to topsoil erosion, soil structure degradation, excessive runoff, deposition, and siltation. Ghulam and Wong (1989) showed that erosion in areas with steep slopes is affected by the slope gradient and land use type. Also, their study indicated that erosion from areas with good plant cover varied from 3% to 15% of the erosion from adjacent bare areas with similar slopes.
The phenomenon of soil erosion is important in Malaysia due to the high occurrence of steepland. Steepland refers to land with slopes with gradients of more than 25° in Peninsular West Malaysia, whereas the corresponding gradients in East Malaysia, namely Sabah and Sarawak are greater than 25° and 33°, respectively. In West Malaysia, 42% of the land surface has slopes with an inclination greater than 20o. In Sarawak, mountainous upland (>33o) occupies 70% of the area, while in Sabah, 22% of the land surface consisted of steepland (>20o) (Shamshuddin et al. 1983). When the native vegetation from these areas is cleared for development, soil erosion and land degradation associated problems will occur if soil conservation measures are not implemented.
The problems of erosion and excessive runoff usually begin at the stage of land clearing. In 2021, a massive and disastrous mud flood and landslides occurred in the state of Kedah, Peninsular Malaysia, which was triggered by land clearing activities. Moreover, the heavy types of machinery used during land clearing which adversely affects the physical structure of the soil was also identified as the cause of the catastrophe, making it more vulnerable to erosion. Ghulam and Norhayati (1989) indicated that erosion of the original topsoil reduced the infiltration capacity of land even after it was planted with new trees and developed a closed canopy.
In general, soil conservation measures are not always implemented immediately after land clearing. Soil conservation measures utilizing cover crops to control soil erosion are effective only after a certain period. For example, complete coverage by leguminous cover crops requires at least three months to be effective as soil erosion measure control after the seeds were sown.
Other factors contributing to soil erosion and sedimentation include the cultivation of crops that are unsuitable for steep slopes. In Malaysia, vegetables are mostly grown on steep slopes in Cameron Highlands, covering an area of more than 2,000 hectares. The reservoir in a hydroelectric scheme at Cameron Highlands, which is located downstream suffers from a severe sedimentation problem due to the intensive vegetable farming on these steep lands. In the past, silt occupied about 1/3 of the total storage capacity of the reservoir and the life span was reduced by half. Similarly, in areas where shifting cultivation is practiced, annual crops such as upland rice and maize are planted on steep slopes. The problem of soil erosion is compounded by the fact that the fallow period is rapidly decreasing, in some cases to less than three years (Awang Noor et al., 2008).
MANAGEMENT AND DEVELOPMENT FOR IMPROVED AGRICULTURE
BRIS and tin-tailing soils
Although the BRIS soils are poor in terms of nutrient content and water-holding capacity, only a few numbers of the crop have been found to grow satisfactorily on this soil. However, with adequate fertilizer and proper soil and water management, many crops especially those that can tolerate drought can be used for the cultivation of BRIS and tin-tailing soils. Some examples of these crops include coconut (Cocos nucifera), cashew (Anacardium occidentale L.), tobacco (Nicotina tabacum L.), watermelon (Citrullus vulgaris L.), passion fruit (Passiflora edulis f. flavicarpa), carambola (Averrhoa carambola), guava (Psidium guajava), sweet potato (Ipomea batatas), Napier (Pennisetum purpureum), kenaf (Hibiscus cannabinus), and a variety of vegetables. Their productivity could be improved when the soil constraints namely poor nutrient content, low water holding capacity, excessive drainage, and high surface temperatures resulting in high moisture crop stress are collectively reduced. For example, improved irrigation systems and mulching were found to be effective in minimizing rapid evaporation and reduced soil temperature. The application of manures and composts is effective in controlling the low water-holding capacity and high infiltration rates of the soils besides providing plant nutrients. However, these nutrients are not sufficient, and additional and frequent application of fertilizers is necessary to maintain good crop conditions. The irregular topography of tin tailings affects crop growth and thus, land leveling is a suitable solution prior to planting on tin-tailing soils.
Some agricultural practices under sandy-textured soils have been introduced to support the production of some crops in these areas. The predominant agronomic measures recommended are the application of soil organic matter, liming and fertilizer management to improve the soil fertility level throughout the cropping period (Soo et al. 2019). For example, a two-fold increase in the yield of crops planted on BRIS soils was reported with the application of Palm Oil Mill Sludge (POMS) at a 6% (7 kg/m2) rate as basal treatments. Similarly, amending sand tailing areas with POMS in conjunction with oil palm Empty Fruit Bunch (EFB) also recorded a yield increase for fruit tree cultivation. Also, co-application of POMS (6% w/w) and EFB bears higher fresh fruit yields compared with that of organic manure treatment such as chicken dung for carambola cultivation. This further indicates that organic matter amendments, particularly POMS and EFB promise to be more effective in improving the productivity of sandy soils (Vimala et al. 2008).
Application of gypsum in conjunction with organic amendments at a rate of 20 t/ha for sweet corn cultivation on BRIS soil produced a higher number of cobs approximately 35,757 cobs/ha. This fruit yield per hectare is reported to be even higher for sweet corn planted on mineral soils with an average of 30,000 cobs/ha. Likewise, the co-application of gypsum and organic amendments at a different rate (40 t/ha) for Napier and kenaf production on BRIS soils also produced a good yield with 13.17 t/ha and 38.66 t/ha (fresh yield of kenaf fodder), respectively. Those applications were applied as basal treatment during land preparation and followed by standard agronomic practice for crop production of sweet corn, Napier, and kenaf (Faridah et al. 2018). In addition, fertilizer management also takes into consideration the high nutrient leaching factor due to the sandy texture of BRIS and tin-tailing soils. Therefore, the split technique and frequent fertilizer applications are recommended not only to reduce leaching losses of N, P, and K but also to increase nutrient uptake and use efficiency by crops.
Sustainable farm management practices are a requisite for the successful cultivation of crops on tropical peat soils. Some of these practices include peat compaction, water table management, drainage system, and liming.
Peat soil compaction is carried out after land clearing under sufficient drainage. The soil is compacted using hydraulic excavators along the intended planting rows. Soil compaction generally increases bulk density in the upper soil layer (10 cm to 20 cm) approximately from 0.1 g/cm3 to 0.3 g/cm3 which is suitable for long-term cultivation. This practice also reduces the risk of lodging or leaning on tall and top-heavy fruits such as oil palm and papaya. Moreover, peat soil compaction also decreases the risk of peat fires. This is because the compacted peat surface is not easily dried out and is capable of holding water longer due to the smaller and less connected pore spaces. However, it must be stressed that peat compaction poses the risk of flooding due to the collapse of hollow pore spaces of the fibrous organic material leading to low permeability (Huat et al., 2011).
Water table management is one of the essential farm operations for agricultural peatlands. This is because the water table influences crop performance, productivity, and surface subsidence. The water table at 30 cm to 50 cm and 50 cm to 80 cm are recommended for shallow (vegetables and sago) and deep-rooted (oil palm) crops, respectively. However, the water table is recommended to be maintained at 50 cm from the soil surface irrespective of crop type for long-term cultivation because this water table regime stabilizes surface subsidence (2 cm/yr), prevents peat fires, and provide adequate drainage for optimum crop growth.
Drainage in peat areas is designed to provide a proper water table for crop growth and to drain excess water during heavy rainstorms/wet seasons to avoid flooding. At the farm level, construction of a higher number of smaller and shallower drains measuring 0.6 m wide and 0.9 m deep with 50 m drain spacing is recommended for both annual and perennial crops. Water control structures with a cascade of close-spaced adjustable weirs are often installed at downstream of each drain to maintain appropriate water table levels in on-farm drains.
Liming is necessary for peat soils due to their acidic nature. The amount of lime applied depends on the acidity of the peat soil and specific crop requirement. Common liming materials used on peat soils include hydrated lime, dolomite, slag, burned lime, and calcitic lime. A liming rate of approximately 20 to 30 t/ha of calcium carbonate is generally applied to peat soils for a wide range of crops. However, liming rate of about 3 to 7.5 t/ha of lime is recommended for short-term crops, but a higher rate is needed for vegetables, whereas annual application of lime of about 0.25 to 0.5 kg lime per planting hole is recommended for fruit trees and perennial crops. However, the frequent liming application is recommended to gradually increase the peat soil pH. This is because liming using a high amount of lime in one application will cause an imbalance of cations, particularly Ca, Mg, and K in the peat soil.
Acid sulfate soils
Acid sulfate soils pose fewer problems when used for waterlogged plants like rice. However, when they are used for dryland crops that require drainage, soil acidity becomes severe. Production of wetland rice on acid sulfate soils (25,000 ha) in the Muda Agricultural Development Authority (MADA) scheme was reported to increase with time. In the early years, when single cropping was practiced, the yield of rice was below 2 t/ha but a two-fold increase (4 to 5 t/ha) in rice yield was achieved when double cropping was practiced for more than 30 years. The increase in yield was due to the prevention of sulphidic properties generated under flooded conditions (Shamshuddin et al., 2014).
For the cultivation of the potential acid sulfate soils for dryland crops, the most appropriate strategy is to prevent the soil from drying out. This is because the pH of the surface soils can be easily corrected without difficulty when the pyritic subsoil is kept waterlogged. For example, in West Johore, some farmers and smallholders in areas with acid sulfate soils maintain the water table about 40 cm from the surface by allowing seawater to enter the drainage channels during high tide. The coconut in these areas produced approximately 70% more nuts compared to that of the bunded areas. Furthermore, Zahari et al. (1989) showed that with the controlled water table, the coconut yield increased from 2,350 nut/ac/year at the onset of the experiment to 2858 nuts after four years. However, contradictory results were reported for cocoa cultivation where cocoa yield was higher under freely drained conditions but recorded lower yield under a controlled water table environment.
Rubber does not grow well on acid sulfate soils. In West Johore, latex yield is about 500 kg/ha/year, which is about half of that obtained in non-acid sulfate areas. Conversely, oil palm survives relatively well on acid sulfate soils. However, in the absence of ameliorative measures, the yield (fresh fruit bunches) is less than 5 t/ha/yr. With fertilization and proper maintenance of the water table, the yield could reach 18 t/ha/yr (Paramanathan et al., 1986).
Vegetable farmers in Malacca and Johore (South of Peninsular Malaysia) generally construct ridges on non-pyritic topsoil and immerse on-farm fields with fresh water. With regular liming and appropriate fertilizer application, vegetable yields for this area are very satisfactory.
A large percentage of steep land in Malaysia occurs at high altitudes and is characterized by a subtropical climate. It could support crops that cannot be grown in the lowlands like tomatoes, cabbages, and other ornamental plants. However, recent advances in crop production technologies, particularly for lowland tomatoes and cabbages have been developed recently and were established in some areas on low land. Despite the steepness, there are also areas where the soils are relatively deep. These factors offer possibilities for crop cultivation in highlands.
The conversion of sloping land from forest to crop cultivation needs to be studied and planned very carefully due to the fragility of the soils and the possible adverse effects on the environment. As such, an appraisal study characterizing the climate, soils, and water resources on the intended steep land is required to obtain information on their limitations and potential for development before any reclamation project can be carried out. Also, the appraisal study will help to identify suitable steep land areas for agriculture development according to land use type. Concurrently, research on soil erosion and conservation is important and is being implemented through national and international collaboration and networking, including research on soil erosion processes on sloping land under tree crops and the development of physical models that can facilitate conservation planning.
The Malaysian Good Agricultural Practice (my GAP) managed by the Malaysian Department of Agriculture (DOA) had introduced guidelines that highly emphasized sustainable management of steep land areas. The guideline has become one of the tools to guide farmers in controlling soil erosion in the country (Zakiyyah et al., 2019). One of the recommendations is to use legumes, vetiver grass (Chrysopogon zizanioides) or kim chiam/ daylily (Hemerocallis fulva) as slope stabilizers. The cultivation of annual crops under rain-shelter also forms the basis of the agricultural system on steep land (Aminuddin et al., 2005). However, its use needs to be controlled due to the risk of soil salinity development under rain-shelter systems. The construction of terraces in agricultural areas is one of the methods that can be practiced by farmers in this sloping highland area. In addition, the use of natural mulching such as rice straw and crop residues, and minimal plowing methods also help to reduce erosion. Agriculture on sloping areas should be developed according to the contour or cultivated with two or three types of crops simultaneously in one area (intercropping).
The steep land agriculture guideline by the DOA (2020) recommended that any activities on agricultural land exceeding 25° gradients must have refrained with the exception of durian (Durio zibethinus). The agriculture guidelines for the management of steep land areas enable these lands to be used for agricultural activities sustainably via controlling steep land erosion effectively besides conserving the environment.
A proper understanding of the characteristics of problematic soils (steep land, peat, BRIS, tin-tailing, and acid sulfate soils) has allowed farmers and plantations to exploit marginal soils successfully in Malaysia. Upon corrections or alleviation of the soil constraints, the crop performances can generally match those of better soil types. However, more than one soil management approach is usually required, and these must be implemented correctly and interactively. Among others, good timing is also essential to ensure success. Nevertheless, it must be cautioned that the cultivation of certain crops on marginal soils entails higher cost, difficult inputs, and good managerial skills but also exposes the farmers and smallholders to a higher risk of failures and competitiveness. It is therefore advisable to regard planting on marginal soils as a last resort rather than an opportunity for development and business. The sustainability of agriculture in marginals soils is greatly influenced by good practices and land use planning. Studies on the determination of the most suitable tree crops, farming systems, and soil conservation measures are necessary to avoid soil degradation and environmental problems. Any development need must be balanced by the prevention of soil degradation, erosion, environmental problems, and depletion of forest resources.
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