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Greenhouse gas adsorption and emission, Leaching requirement for Acid Sulphate soils and Negative Hydrological effects in Peat Domes
There are claims that a Tropical Rain Forest are good for CO2 adsorption from atmosphere. That thinking needs comments.
It should be realized that in an undisturbed forest the adsorption of CO2 will be in principle equal to the emission of CO2. The adsorption of CO2 is caused by growth of trees and by fresh new green material in the forest. Emission of CO2 in an undisturbed forest is caused by dying trees, rotten wood and oxidation of organic material in the topsoil. In principle, the total amount of adsorption of CO2 will be equal to the total amount of emission of CO2 in an undisturbed forest, the balance must be a zero CO2 adsorption/emission. Only when the forest has been cut partly earlier and is protected now, the "sink" of the forest in total CO2 will increase during the period with new growth of trees; but only during this growth period.
Primary Peat Forest
However, in undisturbed peat soil areas the total amount of adsorption will be bigger than the total amount of emission. For peat soils in the tropical rainforest climate that amount will be about 2-5 tons CO2/ha /year. This adsorption of CO2 is caused by the yearly increase in thickness of the peat layer in the undisturbed peat forest of the ombrogenous peat soil. According Driessen and Subagjo, of the Soil Research Institute in the nineteen seventies, the average increase in the last 5000 years was 1.8 mm/year for ombrogenous peat soils, or about 2.3 tons CO2/ha/year, or 63 g C/m2/year. (this includes measurements based on C14 age determination of the peat). For the about 10 million ha of peat soil in Indonesia that means in total 23 million tons CO2/year, or 6.25 x 1012 g C/year has been conserved in the different peat soils of different age. (5000 years for the oldest, down to 1000 years for the youngest.). In all other swamp forests there is no growth of organic layer and the CO2 balance of adsorption and emission will be zero. To see the maps of the Nation Wide Study of coastal and near-coastal swamplands of Indonesia (1984) click Nation Wide. This study is still the most reliable and intensive swampland survey ever be done at Nation Wide level; concerning: soil types-depth of peat-natural vegetation-agro climate-hydrology and topography-tidal movements/ranges/levels-salinity. Click the map you want to see or Right Click the map you want to download and use Save Target as.. (for Windows Internet Explorer) or Save Link as.. (for Mozilla Firefox))
When the Primary Swamp Forest (including peat forest) will be reclaimed for new Agricultural land than about 200-400 tons CO2/ha will be lost by burning and wood cutting. (That equals 54.5 - 109 ton C/ha, which is less than the non-swamp tropical rainforest, that could be 120-150 ton C/ha, this figure is based on Houghton, 1995 a.o) The CO2 content of the trees and green material depends on the type of tropical forest that depends very much on soil type and its hydrological characteristics. Further an important part of the wood will stay on as a "sink" of the CO2 when it is used for construction, furniture etc.
Plantation Forest and Agricultural land
When new plantation Forest will be planted a yearly adsorption of CO2 will exist caused by the growth of the forest. After cutting the forest again in principle the same amount, as will be adsorbed during the growth of the forest, will be emitted. The plantation forest will have a smaller "sink" than the Primary swamp forest.
Agricultural use (including oilpalm and rubber plantations) of swamp land in Lowlands will also result in principle in a zero CO2 adsorption/emission balance. Each year the CO2 of the grown green material will be emitted again with a relatively small "sink" in comparison with primary forest and plantation forest. (The exception will be for the for the peat soils that will have a yearly emission of oxidized peat to CO2: see webpages Impact .
Effects of cattle/ruminants, the true story
In the manure and emissions from cattle/ruminants some of the CO2 will change to CH4 which is a more serious greenhouse gas than CO2. But the largest CH4 emission is from natural wetlands and the wetland/irrigated ricefields, that are not regular dried; all will have bigger CH4 emissions in total than ruminants. However within 9 years all the emitted CH4 in the atmosphere will be oxidized again into CO2 and the Carbon balance remains zero. (Besides; Tidal Lowland rice fields will have no significant CH4 emissions compared with most wetland/irrigated rice fields, because they are mostly regularly oxidized by the tidal movements). However it should be also realized that increase of the bio-industry in the world will also increase the amount of CH4 in the atmosphere. Although better farming practices can reduce the CH4 emissions considerably.
So undisturbed forest, plantation forest and agricultural land, all have zero balance of adsorption with emission. Only land use changes and farming practices will change the "sinks". Further drainage of peat soils will contribute to increase of CO2 in the atmosphere (see also webpages Impact and Problems).
Sinks in various land uses.
The various land uses only have different quantities of sink of CO2 and changes in land uses might change the sink of the land use. For Indonesia the following sink values might be valid:
So if you want to calculate the sink loss of the cutting of forest into a new land use than do not forget to deduct the sink loss of the forest with the new land use sink.
By draining the peat soil up to 70-100 cm not only high CO2 emissions will occur, but also the drainage potential in the peat soils will disappear and after 15 to 20 years most deep ombrogenous peat soils can not be drained any more by gravity, while pump drainage is in a tropical rainforest climate not an economic alternative. (Needed pump capacities per ha, more than three times larger than in Holland, for instance). See also cross-section figure of the peat dome below.
It means only a limited amount of the total peat dome can be drained and oxidize and will give CO2 emissions by cultivation. Total calculations of the C quantity of a peat dome are unrealistic; it should mention that only a limited quantity of it can be oxidized by lack of drainage potential.
Not drainable peat lands will return to peat forests with a low tree density and marginal growth of the wood.
Peat soils and hydrological Effects
Subsidence and drainage potential are the most important factors that influence the potentials of peat soils for sustainable reclamation and its recommended use.
The initial subsidence just after reclamation of the virgin peat soil is about 40-60 cm in general in Indonesia, while the yearly subsidence after reclamation is about 10 cm per year when tree crops like oil palm are grown. It means that a subsidence of 2 meter is not unusual for the first 15 years when the peat is reclaimed. With older reclaimed peat soils there is a tendency that the subsidence rate reduces, resulting in a peat subsidence of in total 3.5 m for oil palm plantation areas 40 years after reclamation. These figures are based on actual measurements in Indonesia and Malaysia.
Because of this subsidence problem the drainage potential could dramatically decrease with time and peat soils may become not suitable for any agricultural use. (Drainage by pumping is not an option for Tropical Peat Soils). It is therefore essential that decisions for reclamation of virgin peat soils is combined with an assessment of the sustainable drainage potential based on a drainage lay-out of the Scheme. When the peat soils are already reclaimed and drainage potential is reduced, decisions have to be made concerning the proper land use that sustains its agricultural/forestry potential.
Other land uses that require less deep groundwater levels will have a lower subsidence rate and might be an alternative for areas with reduced drainage potentials.
You can also download more information concerning Ombrogenous peat swamps.(pdf file; right click Download and use Save Target as.. (for Windows Internet Explorer) or Save Link as.. (for Mozilla Firefox))
Negative Hydrological effects in Peat Domes caused by artificial drainage in adjoining agricultural land. True or Not True?
A number of researchers claim that drainage at the border of a peat dome results in a drop of land levels by subsidence in the peat dome and contributes to excessive drying of the peat surface, making it extra sensitive to fire hazards. The cause is, according these researchers, the extreme high permeability of the peat soil.
The effect of continued subsidence in the adjoining developed area on the border of the upper dome could have an effect of subsidence in the peat dome up to 1000 -2000m from this border. Caused by the drainage effect of the adjoining developed border areas there are also lower water levels on the peat dome resulting in subsidence. This is especially the case when the developed border area also consist of deep peat. In case the adjoining developed border area of the peat dome consist mainly of clay soils or shallow peat soils the effect on the peat dome is minimized, because these soils have a minor drainage effect on the peat dome.
However what is most important? The top of the peat dome as supplier of water to the adjoining land. That could diminish dramatically when the area of a conserved central peat dome becomes smaller. What counts is the total surface area of the flat peat dome in the middle part (as a storage of the supply water to the lower areas; = rainfall minus evapotranspiration) in relation to the total perimeter length of the peat dome at the border. That relation determines how long interflow(=sub-surface flow on a slope) from the peat dome to the lower developed area will occur during a dry spell. Interflow will be the most important water source to keep the water tables high in the developed deep peat areas on the border of the peat dome. Besides a water control system in the developed peat area will be important here. Keeping water tables high is essential in these areas to prevent a subsidence to a level no drainage will be possible anymore. (See drawing above)
The peat dome slope on the borders might have a slope of 2-6 m/1000m. In other places slopes of 0.75 m/1000m have been measured. These slope differences are clearly related to different permeabilities that are related to the type of peat; with fibric peats having the highest permeability (and lowest slope) and sapric peats the lowest permeabilty (and highest slope).
Why do peat domes burn during extreme dry seasons? The top 40 cm will dry out by evapotranspiration. Excessive logging produces wood remants that easily burn. A fire in bush/grasslands, often occurring also in undisturbed areas along rivers, extends into the adjoining peat dome, especially in combination with excessive logging in the peat dome. Prevention: stop excessive logging on peat domes, and start a more sustainable forestry system only on the borders. See web page Problems
Greenhouse Effects from drained and developed Peat Domes. The subsidence on peat domes depends on the depth of drainage, with water tables at 80cm causing 10 cm subsidence per year. In first instance most of the subsidence is caused by compaction of the peat sufaces when the groundwater levels are lowered. But a minor part of the subsidence consist of decomposition of the peat by oxidation, resulting in CO2 emissions. With time the rate of subsidence will decrease by a reduced rate of compaction, but the amount of decomposition (=CO2 emission) will be constant. The whole subsidence problem, including the CO2 emissions could be reduced to a minor problem when water tables in the developed peat areas could be kept high. (about 40-50 cm below surface)
It means high watertables in the developed peat areas on the borders of the peat dome have three positive effects: 1)Sustainable drainage of the developed areas will be possible and 2)green house effects will be minimized while 3) central peat domes might be conserved to enable sustainable cultivation in the developed peat areas.
Most of the rice soils are actual or potential acid sulphate soils. Therefore High Rice Yields in Swamp land require leaching/percolation of the root-zone of the rice plant. Most effective this will be during land preparation and the early stages of rice growth. In some cases this should be followed by repeated cycles of shallow drainage and sun-drying of the root-zone at the end of the tillering stage of the rice plant. Leaching/percolation requires mechanized land preparation and supply by rainfall and irrigation and an adequate drainage system of which sub-surface drainage is the most effective way to provide percolation. For more information on sub-surface drainage systems see WebPage Design Micro.
Leaching/Percolation has a major influence on rice potentials in the Tidal Swamp areas and is a key explanation for the physical problems encountered in these areas when insufficient percolation occurs. Physiological and foliage diseases in the rice plant caused by stagnant groundwater are the most obvious reason for low yields in the swamps
Percolation requires: 1) a certain Effective Drainage Depth during the growing season(=average water levels in the adjoining tertiary canal are about 30-40 cm below field level surface) and 2) sufficient water supply by rainfall or irrigation (tidal flooding or pump irrigation).
The question remains how much leaching/percolation is required. About ten years ago we concluded, from collected data in rice fields, that about 8mm/day percolation is required for yields of more than 3 ton/ha. With data we collected during ISDP we concluded that this figure for required leaching/percolation quantities can be lower. About 5-6 mm/day during mechanised land preparation and early growth, while 2-4 mm/day for the remaining growth stages of the rice plant would be sufficient. See graph Rainfal, Leaching and Waterlevels for the leaching quantities in a test area during one year monitoring. In non-acid areas the the leaching requirement may be even lower and demands only some leaching based on natural rainfall during land preparation.
A frequently asked question concerns the influence of the depth of the pyritic layer on the rice yield potential. In Indonesia we never found a relationship between yield, acidity and the depth or content of pyrite in the pyritic layer. However a relationship of yield is found with the leaching factor, which also often is related to the position in the landscape (high or low= 10 cm surface level difference can make all the difference) or the distance to the river or the nearest canal, or if the canal is double connected or not etc.etc. So you must understand the hydro-topographical characteristics of the site to know the potentials of the acid sulphate soils.
The need for high percolation rates for poorly drained rice soils has been noted also by Cheng (1984) in China. He recommends percolation rates of 7-20 mm/day, depending on the soil types and farming practices. Research in China showed that by improving the percolation rate and lowering the groundwater table in the off-season causes padi yield increases from 2-3 ton/ha to 6-8 ton/ha. This was attributed, among others, to the changes in the types of organic matter by oxidation. By oxidation the organic matter became active in improving fertility. The C/N ratio will improve dramatically.
Continued submerging without percolation increases the accumulation of CO2, H2S, organic acids and reduced iron, often in toxic quantities. Percolation increases the dissolved amount of O2 content of the groundwater and will increase the ability to get rid of toxic substances. Low percolation rates reduced the aerated porosity in the soil. This causes that the uptake of nutrients by rice roots will become slower and the need for the application of chemical fertilizers will increase. Low percolation rates can be found in areas subject to interflow. See also Web page Problems.
Greenhouse effects caused by methane production in wetland rice fields. Neue et al. (1989) of the IRRI in Manilla states that for rice fields with a high organic matter content flushing and periodical drainage will be essential for high yields and to prevent the formation of methane. Organic matter decomposition in submerged rice soils is closely associated with methane formation. This methane production can be prevented by high percolation rates or aeration periods.
Leaching trials in Model areas of ISDP. The effect of the leaching has been measured for the chemical characteristics of the soils by Sutrisna et al (2000). Most remarkable were the improvements for Soluble Ferrous Iron in the groundwater for the first 50-100 cm from the surface and the dramatic improvement of the C/N ratio in the surface layer.
Percolation and drainage versus water retention for acid sulphate soils
Deep drop of groundwater during long dry season. There is one major misunderstanding in the existing recommendations for soil/water management in Tidal Lowlands of Indonesia. It is assumed that water retention in canals can prevent the drop of groundwater levels below the pyrite layer of the acid sulphate soils and prevent acidification of the soil. There is now sufficient prove that this assumption is wrong.By daily groundwater observation for many years during long dry seasons such as in 1991, 1994 and 1997, but also during August 1999 it became clear that the groundwater table can not be maintained above the pyrite layer. This drop of groundwater table is independent of the water levels in the canals. Groundwater levels in the fields almost completely depend on the balance of rainfall and evapotransporation during relatively dry periods. Canal water levels and even the micro system at field level can not prevent this. The field ditch system (micro-system) is only effective for supply objectives in areas with tidal flooding types above land level, but not for areas with flooding types below land surface. (the latter flooding types cover the majority of Tidal Lowlands). Even the sub-surface drainage system has only a limited potential to supply enough water during a long dry season.
Because there is in Indonesia enough rainfall for leaching the main objective for water management in acid sulphate soils is leaching/percolation by controlled drainage and flushing the canals from acids. (This has been proven also by using the SMASS computer Model, Bronswijk and Groenenberg, 1992) By leaching you will get rid of the toxic elements formed during a long dry season and continuous percolation will prevent that the toxic elements may reach the rootzone of the rice plant during early growth. Data collected in the Model areas prove that the recommended leaching/percolation technique is successful to counter-balance high acidity and improve conditions in the field.The relation between high yields and high percolation rates were also found in the Indonesian swampland projects in South Sumatra province. Percolation rates were measured by daily recording of rainfall, irrigation, water levels and evapotranspiration at selected locations. The deep drop of the groundwater has not only negative aspects. There is also ample prove that a deep drop of groundwater tables even has a positive effect on pH and fertility in the surface layers and that rice crops planted after a long dry season are considerably better performing than after a normal, quite wet, dry season. Among others the experience is found in Telang-Saleh, Palembang. The wet season crop of 94/95 resulted in a very high yield following an extreme dry year in 1994. It is however of major importance that for this rice crop after a long dry season also sufficient leaching is applied during early growth.
Comparison with Australian conditions. It looks that Australian conditions and objectives of the control of acidity are different from those in Indonesia. An Australian computer model, made to control acidity, worries mainly on acidity released to the canals. Completely different from the objectives in Indonesia, where the acidity release to canals and the environment is a limited problem which also can be solved permanently by one-way flow by gate operation. The objectives in Indonesia concentrate on how much leaching is required to prevent acidification and toxic conditions in the top soil during the growing season after the yearly, un-avoidable, pyrite oxidation in the dry season. The reason of the difference of approach is not clear for me at the moment; may be there is more and longer oxidation of pyrite in Australia during crop growth, or the rainfall pattern is not favourable in comparison with the Indonesia. A major disadvantage of the Australian approach is that it looks like that it only slowly solves the problem. This contrasts with the Dutch approach where previous acid sulfate problem soils, by continuous leaching of the acids, now belong to the richest areas for agricultural production. Anyhow Computer simulation of Indonesian conditions (Suryadi, 1996) shows also that leaching during land preparation for rice cultivation and flushing the canals by the tides will be in most cases sufficient to control acidity.
What says practical experience?: There are a number of publications which maintain that leaching of acid sulphate soils is a slow process. (See for an overview: To Phuc Tuong et al.,1992). This statement is clearly challenged in practice. It appears that mechanized land preparation and near surface groundwater flows based on terrain height differences or a dense ditch system can effectively remove acids in a short time and good rice yields can be obtained. Not only the acids can be removed but also the pyrite will disappear from the surface layers by oxidation in the dry season.
The need for leaching. In Literature little can be found about leaching in recent publications. A likely explanation is given by To Phuc Tuong (1992) who states that the leaching process of acid sulphate soils involves many complicated mechanisms which are not yet fully understood. He notes however that farmers in the Plain of Reeds in the Mekong Delta are successful upon repeated cycles of puddling and flushing of the rootzone of the rice plant. This success of the Vietnamese farmers shows in the latest satellite images of the Plain of Reeds. These images indicate a dramatic increase of the cultivated rice land area compared with the satellite images made just 10 year ago. To Phuc Tuong et al.(1992) also concluded from a number of trials that the leaching effect of the acid sulphate soils was greatly enhanced by the land preparation and by sun-drying. My own recommendations for soil and water management are found in Webpage Operation.
Husson (1998) hardly mentions the word leaching but observes that low lying fields do not show improvements, even not after a number of years of cultivation. (apparently there is not sufficient effective drainage depth; my comment). This was in contrast with the results in the medium and high lying fields, which showed major improvements in yields after 2-3 years with repeated cycles of land preparation and cultivation. These rice fields all have a dense system of canals and field ditches. See Webpage Scheme Photos and Webpage Design Micro for examples of an intensive system in Indonesia.
Mechanised Land Preparation: the key to success in acid sulphate soils
The need for mechanised land preparation with pumping during this period. Kselik (1990) conducted trials in South Kalimantan for the Dutch funded LAWOO research project. He concluded that water could be maintained much longer in puddled soils by mechanised land preparation, including pumping. From continuous observation of the crop deficiencies during the trials, it was found that puddling had a beneficial influence on nutrient availability (Less fertilisers required). Nutrient deficiency symptoms were reported to occur later and were less severe in the puddled plots. The trials were conducted in a very acid area with abandoned sawahs. The reported advantage of the water management + puddling is 1.5 ton/ha without any fertiliser use (an increase from 0.9 ton/ha to 2.4 ton/ha in the first year of the trials).
Reducing the amounts of toxic Agricultural Chemicals. Another very important advantage of mechanised land preparation is the possibility to plant large areas in a short time. This will reduce the hazards from rat attacks by the possibility to synchronise rice planting. (There will be less chemicals required to control the rats). Puddling will reduce water losses and improve water control. Mechanised land preparation will cause adequate weed control and therefor there will be no need for herbicide use. The stronger rice plants obtained by proper water management and mechanised land preparation will make the rice less vulnerable to diseases and pests. Mechanised land preparation, combined with pumping during land preparation, will have therefore an additional advantage: A major reduction in the need for agricultural chemicals.
NGO's have been critical of the excessive use of toxic Agricultural Chemicals in some demonstration plots in ISDP. See also my Webpage Impact, pollution agricultural chemicals. Mechanised land preparation combined with leaching is the answer to tackle this problem.
Reducing the amounts of water losses. In Vietnam it has been noted that repeated cycles of mechanised land preparation significantly improved water control in the highly permeable surface layers. After a number of years the plough-layer could maintain water layers on the surface longer and and more often, contributing highly to better yields. After a number of years the need for frequent root-zone leaching diminishes as the toxic conditions have been greatly improved and more attention can be given to better water control.
An graphical example of a farmer who applied mechanised land preparation with pumping during this period is found on WebPage Model Areas, best field in SK 4
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