Webpages with more general information
Webpages with more detailed information.
Greenhouse gas emissions
Developed Rice fields in already reclaimed land have no or minor CO2 emissions. All fossil peat has been already oxidized and the remaining clay soil will not have CO2 emissions from fossil peat. However Rice fields throughout the world are a major contributor of CH4 emissions (together with the wetlands). But that greenhouse gas effect will only exist when anaerobic conditions will persist for considerable time in the rice field. The advantage of rice fields in Tidal Lowlands is that there is normally a constant flow of oxidized water in the Tidal Lowlands that reduces the effects of CH4 emissions in Tidal Lowlands..
CH4 gas will be oxidized in the atmosphere within 9 years after the emission from the rice field. It means that only with an increase in the area of rice fields this will contribute to higher levels of CH4 in the atmosphere. (except when the new ricefield is in a former wetland)
The conclusion is that increasing the yields of rice (including better water management) in existing areas of Tidal Lowlands will not bring any significant increase of greenhouse gases from Tidal Lowlands.
Acid Sulphate Soils
Presence of Acid Sulphate Soils is a major problem in the cultivated Swamplands of Indonesia. If this problem is not recognized and solved, the result will be a low yield and the environment will deteriorate to a level the people will abandon the area. Some mitigating measures are discussed below. More information is also found on page Management.
Over-drainage is a term frequently used when discussing problems in acid sulphate soils. It suggests for many people that the intensive canal system is the problem of the acidity and water retention is the solution to the over-drainage problem. In my own experience an expert of IRRI Manilla, thought back in 1991 in the same way and strongly criticized my field trials for the Swamp II Research project for leaching of acid sulphate soils!
Recommended Approach to solve the Problem: First of all should be recognized what kind of over-drainage is present in the field. There are two types of over-drainage , each with a totally different solution.
The other major problem for agricultural development is the presence of peat soils of extreme low fertility. Cultivated Peat soils may also subside over time to levels below water levels in the river. In that case drainage by pumping will be required which is in the wet tropics not economic. See also abandoned areas with peat soils.
Exposed acid sulphate soil material.(pyritic)
Oxidized pyritic soil material will release large quantities of acid groundwater to adjoining canals at the beginning of the rainy season. The red colour of the canal water is caused by oxidized iron. The water in the canal is extremely acid and can not be used for domestic uses and will cause severe corrosion on control structures. Only a few fish types will survive in this environment. Acid canal water for a long period is a good indicator that there is limited flushing capacity in the canal system. Good water management, including flushing of canal water at springtide, reduces the length of the period with acid canal water. Better access at short distances to nearby rivers is also very important. The best flushing results need control structures in the canals. One-way flow in the canals, induced by control structure operation in the canals, is the only available solution to flush out acid canal water at places far away from the river.
Stagnant water conditions in fields. Effect of seepage of extreme acid water from dike.
Stagnant water conditions in acid sulphate soils are the main cause of severe toxicity and acidity in the rice fields.
Low percolation or leaching quantities cause stagnant water conditions. The main reasons are an absence of an on-farm water management system and so-called ditch wall effects in tertiary canals which prevents leaching of the subsoil by rain or tidal irrigation water. Seepage of extreme toxic groundwater from slightly higher locations may also cause severe problems (interflow). Minor elevation differences of 10 cm are sufficient to advance to major difference in acidity problems. See photo on the left showing an abandoned area with stagnant water, bordering a slightly higher area with rice fields. In other areas only a small part, under influence of direct seepage of toxic groundwater, is affected. See photo on the right which shows a dike with very toxic soil bordering a rice field.
The most important mitigating measure is an improved water management system with supply and drainage, including an on-farm water management system. Access of canal water must be easy to the fields, requiring a short distance between tertiary canals. This enables increased water supply and percolation rates in the low lying interflow areas. In some cases the construction of an interception drain at the border of the high and low area may improve the conditions. But most important is the construction of an on-farm water management system. See Web page Management for more information.
Literature often focuses on the chemistry and acidity of the acid sulphate soils. For that reason applications of lime to the soils are recommended as the main measure to improve conditions. In Indonesia this solution is too expensive and also not required. Leaching and oxidation of the rootzone, which keeps away toxic elements and improves the C/N ratio dramatically, are good ways to make the acid sulphate soils suitable for Indonesian conditions. I also believe that in more drier climates like in Thailand and Vietnam (my own experience) and probably also for areas in Australia, stagnant water and lack of leaching/percolation is the main cause that conditions deteriorate to levels no cropping is possible anymore.
Areas are abandoned because of severe acidity or because of the presence of peat soil with extreme low fertility.
Melaleuca re-growth in former rice fields.
To reclaim abandoned area requires a high investment in improving the infra-structure. Usually no farmers can be found anymore. When present in large continuous blocks the Forestry option should be considered as a more economic alternative. In other cases large-scale rice farming could be considered.
Acid sulphate soils. Re-growth of Melaleuca in abandoned fields with acid sulphate soils is easy. The trees come out often spontaneously and are most suited in these conditions. In other cases re-planting may be required. It should however be not forgotten that all abandoned areas with acid sulphate soils have a potential to be used for rice again by the introduction of the proper technologies. See Index for more information.
A new alternative emerging is the planting of Albizia in abandoned swamp areas. This requires the involvement of the farmers, who abandoned the area. (they usually still own the land).Sometimes it is difficult to get them interested again in cultivating their abandoned land. In Jambi province, a huge pulp factory promotes the planting of large areas with Albizia trees in the swamp region. In the Pamusiran Scheme, the Min. of Forestry in the Prov. of Jambi encouraged the farmers to plant Albizia seedlings in an area of 350 ha. This requires the digging of ditches, each 50 m and 1.00 m deep. These ditches should be connected to the main drainage infra-structure. After five years the trees are ready to be processed to pulp. The project looks promising, but would require a yearly maintenance of the ditches. The economic prospects are good for smallholder Albizia plantations. The main limitation will be transport and its costs.
Forestry on Peat Soils in natural conditions is not sustainable!!! Forestry concessions for selective cutting have been licensed on peat soils over major areas of the 16 million ha peat soils of the Tidal Swamps in Indonesia. Nobody realised in the past that Forestry by Selective Cutting can not be maintained and trees show no re-growth after the valuable wood has been cut. Even a few years ago experts still thought this re-growth was possible; only better protection was all that was required. How wrong they were! The explanation is that most of the minerals required for new tree growth are not present in the peat soil, but in the living organic matter and the recently decomposed dead organic matter of the trees. Additional burning of the organic matter of the surface will mean again loss of minerals, because the ash with the minerals easily wash out of the root-layer. Wood removal by selective cutting means the minerals are gone and no minerals are left in the already extremely poor peat soils.
Because Forest Concession Holders on peat soils realise after a number of years no valuable wood is left in the area and they see no re-growth, they aim to change the area into pulpwood or oil palm plantations (with deep drainage and extensive mineralisation of the peat soil with fertilizer applications). This is now happening in Indonesia. After an extreme dry year (1997) the Concession Holders clear-cut the remaining forest on the peat forest, which had suffered from the drought and the peat fires. They than change the area into pulp-wood and oil palm plantations. There are two problems with this practice:
Peat soils, not drainable. In Malaysia numerous examples can be found of abandoned areas where tree crops previously were planted, but the peat soil now has subsided below the water levels in the river. (effective drainage depth is zero). They are not drainable anymore by gravity and pumped drainage in the wet tropics is not economic, certainly not for tree crops. These abandoned not drainable peat soils are not suitable anymore for any use, also not for forestry. It is extremely important that peat soils planted with tree crops remain drainable after subsidence, so that future generations will have also something left to plant. For some regions sustainable drainage is possible, in others this will be impossible. Hydro-topographical surveys are essential before ever a concession should be given for tree crop cultivation in peat soil. In general can be said that peat soils opened up for tree crop (oil palm) and pulpwood plantations require a tidal range of at least 3-3.5 m in the adjoining river. Next the level of the bottom of the peat layer should be situated at least above the mean water level in the adjoining river to sustain an effective drainage depth.
At the moment there is high pressure in Indonesia to open up the peat lands to plant oil palm. In many cases areas peat lands are now planted with oil palm that can not maintain drainability. Only a limited number of those peat lands have a potential to maintain its drainability after subsidence!
Peat soils, hydrophobic . Re-growth in abandoned reclaimed areas with peat soils of an extreme low fertility is most difficult. By repeated cultivation the soil has become so low in fertility that re-planting requires special treatment. By direct exposure to sun light during cultivation the peat soil becomes irreversible dry in the surface layer and will change into dry pellets. (=hydrophobic peat soil, that means no biological activity is possible anymore for these dry peat pellets). Direct sun-light exposure may raise temperatures in the peat surface layer to more than 70 degrees Celsius and will cause irreversible drying. Adding mineral soil, sand or volcanic ash to the surface will prevent this increase of soil temperature, but in practice is excessive expensive. At least 40 tons of soil per hectare is required for a sustainable solution of the problem.
Below I propose for Peat soils a sustainable alternative: Forestry with minimal controlled drainage.
Annual crop cultivation always will include, for part of the year, direct sun light exposure of the surface layer. Therefor only trees are suitable for such peat soils as they can provide permanent soil surface cover. For re-planting of trees the seedlings should be planted in 30-40 cm deep planting holes to which zinc and copper elements has been added to guarantee healthy growth. Shallow controlled drainage would be required. (in contrast to deep drainage for pulpwood and oil palm plantations) Drainage ditches (with canal collectors) should be constructed each 100 m to promote the oxidation and the decomposition of the peat top layer. Mulching of the top-layer will be essential. Only when sufficient nutrients have returned to the toplayer, the newly planted trees will grow. This high investment may be only economic when high value Ramin trees (Gonystylus bancanus) are planted. It is essential that after a number of years a balance is found by shallow controlled drainage between decomposition and accumulation of organic matter.
In this respect I claim, based on my field surveys, that groundwater levels in peat soils in Indonesia drained not deeper than 30- 40 cm below surface, will not cause significant subsidence and will not cause an oxidation exceeding the organic matter accumulation. In natural conditions there are also very large differences in tree growth between peat soils where groundwater drops to 40 cm during dry spells and peat soils which contain water in the surface layers for long periods.
Maintaining water levels at 30-40 cm below surface by controlled drainage might be also a solution for the pulpwood plantations on deep peat soils that will experience growth problems for the acacia and other trees. When tidal range is at least 3 m on average and present topo-level of the peat is at least 60 cm above mean water level in the adjoining river or water course than there are reasonable prospects the pulp plantation can be maintained with reasonable growth. When one or more of these criteria can not be met, I expect that the prospects for the plantation are meager.
Also for peat soils with severely degraded Swamp Forests the Forestry option is an attractive alternative. Wood enrichment will be required by planting with valuable forestry trees in between the existing vegetation. The construction of drainage ditches each 100 m to promote the decomposition of the peat top layer will be sufficient to produce sufficient minerals for growth of the forest. Also here Ramin trees are recommended. This Forestry system already existed 60-70 years ago in Riau province, Sumatra island.
The question remains: Is sustainable Forestry on peat soil possible?
So far I know, the only agricultural system including drainage of peat soils, without loss of peat by oxidation, exists in Holland for the grasslands/meadows. Here water levels are kept high throughout the year by a very intensive canal/ditch system. The peat top layer has been enriched to provide just sufficient minerals for an abundant grass production. However I do not believe this system will work in Indonesia. In Holland the peat grasslands already suffer during hot summers and the hot sun in Indonesia will surely cause excessive oxidation of the peat. But based on my experience in the Peat Swamp Forests of Indonesia and Malaysia I am convinced that a relative wide extensive canal/ditch system (with water level control) can maintain the peat layers in the tropical rainforest climate of Indonesia. The challenge will be to introduce a drainage system with low maintenance costs. Maintenance costs of drains are expensive in peat soils. A mineral enriched surface layer will be essential to sustain the wood production at a high level. (Especially zinc and copper are critical). I consider a canal system with relatively high water levels also the only way to prevent wild fires over large areas when the peat lands are still covered by young trees.
There is a high need to introduce a sustainable Forestry system on peat soils.
This might prevent the total disappearance of the Peat Swamp Forest
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