Webpages with more general information
Webpages with more detailed information.
Land & Water Use
All Swamp Schemes are situated in the Tidal stretch of the rivers. Most areas in Tidal Swamp Schemes are rain-fed. This limits wetland rice to only one crop per year. Increasingly farmers are planting soybean or maize as a second crop. Few farmers plant a second rice crop. Although there are at many places potentials for pump irrigation in the dry season in order to grow rice, the practice is very limited and mainly found in experimental plots. In South Sumatra province a trial on large scale is going on to extend the technology and required infrastructure for two rice crops per year in areas with tidal irrigation potentials.
Beside foodcrops, many farmers are also planting tree crops, especially in the coastal areas of Riau province. Tree crops, at canal distances of more than 3 km from the river, require a tidal range of at least 3-m in the adjoining river. When planted within 1 km from the river the required tidal range is 2-m.. Even less tidal range is possible when they are planted on raised beds. In many cases tree crops are also the favorite crop when the adjoining river is saline for a large part of the year, or when the land is situated more than 50 cm above Mean High Water. Saline areas with less than 1.5- m tidal range are the favorite area for fishponds.
Successful Tidal Swamp Schemes are characterized by the application of proper water management and mechanization/advanced post-harvest management combined with credit availability for farmers. The water management for Wetland Rice in Tidal Swamps requires leaching of toxic elements from the root zone; dryland crops and tree crops require groundwater levels 40-80 cm below land surface. For that reason field ditches should be made at a 25-m spacing. For dryland crops and tree crops these ditches are 50-90 cm deep, for rice 30-40 cm deep. Soils are shallow peat (muck) soils or acid sulphate soils. Based on this intensive water management system the swamp soils can be made suitable for agriculture.
Failures in development are related to insufficient drainage, leaching and flushing. It is impossible to keep water levels above the pyrite layer of the acid sulphate soils during a dry season. That means sufficient leaching is required to remove the formed acids from the soil. Publications from Australia concerning acid sulphate soils seem to worry mainly about acidity release to the environment, a problem which is in Indonesia of limited importance (See below under: What to improve?) For that reason the Australians mostly recommend water retention. However to recommend water retention in Indonesia and Vietnam has a disastrous effect on the yields of rice. Here leaching and flushing the canals is a main objective for water management. See Webpage Thesis, section Deep drop of groundwater, and section Need for Leaching for my comments. For the effects on the environment See webpage Impact for acid release to environment.
In areas suffering from acidity problems it is a popular saying that they suffered from over-drainage. That word gives often a very wrong impression of what is really the problem. It suggests that the large and intensive systems of drainage canals and field ditches are contributing to the problem, while those canals and ditches are essential in solving the problem in most cases. The focus of everybody, working in the swamps, should be on flushing and leaching. Stagnant water is mostly the problem. Farmers should immediately note when their rice crops suffer from stagnant water, showing blast or brown spot or retarded growth, to open all the gates and start flushing and leaching their fields! A relatively dry field in this stage is better than a field with stagnant water in the root zone! Notwithstanding real over-drainage exists in the Tidal Swamps of Indonesia. See Design Macro for an example.
Leaching of soils is connected to accumulation of acids in the canals. See under What to improve? on this Webpage Scheme photos how water quality in canals could be controlled. (See below).
Most deep peat soils in the Tidal Swamps of Indonesia are not suitable for agriculture because they become hydrophobic after exposure to direct sunlight. Also Forestry by Selective Cutting under natural conditions is not sustainable on these deep peat soils. For these Forestry Concession Areas a new Forestry system is proposed based on an extensive system of shallow drains with water level control. This Forestry System can maintain the peat layers for the future. Existing Peat Swamp Forests could be enriched with new Forest Trees and severely degraded forests could be planted with Ramin trees as an attractive alternative. Tree Crop plantations (like oil palm) on deep peat soils can not maintain the peat layers and therefor are only suitable when the bottom of the peat layer is situated above mean sea level and the tidal range in the adjoining river is at least 3-m.
Drinking water supply is important in Tidal Swamp Schemes. The ISDP project supplied large containers for rain water storage with great success.
Poultry development suits the Tidal Swamp environment. Bran meal obtained by processing rice grains (dedak), crushed whole maize grains and dried fish-heads are in a mixture excellent for poultry feed.
A major effort has been the development of Water Users Associations who will take care for the tertiary development, operation and maintenance. In Tidal swamp Schemes it is of utmost importance that there is an operational water management system, based on an appropriate infrastructure.
Mechanised land preparation, broadcast seeding combined with pumping during land preparation (especially for the second crop when to soil must be puddled) is the key to successful swamp land development in Indonesia. Large scale introduction of this technology is essential but lacks at the moment sufficient support. The Water User's Associations should play a major role in the purchase and the operation of the mechanization tools. See my Webpage Thesis, need for mechanisation. Also in the Plain of Reeds of the Mekong Delta in Vietnam, the large scale introduction of mechanized land preparation has been essential. After a number of years the introduction of mechanised land preparation also contributes to better water control in the fields. This all requires also the availability of credit facilities for the farmers.
Main canals and control structures play a crucial role in flushing the acid water out of the system and maintaining the required water levels in canals. Water flows can be regulated by gravity flow, using control gates, in the Tidal system. Dead-ended canals should be avoided at all canal levels, including tertiary and quaternary canals. Box culverts made by the farmers are needed to maintain connections of canals at tertiary levels when they cross the (field) roads. Structures which require frequent operation should be located close to the home-steads. Fiberglass removable flapgates are a new promising development. They can be oprated for supply as well as drainage, depending on the requirements. Pump irrigation during mechanised land preparation will increase yields considerably. At present no operational pump irrigation system exists for dry season irrigation. They need a system based on supply.
The infrastructure water management system demands a strong community with a high social capital, willing to co-operate with each other. Potential high yields and income will be the driving force.
What to improve?
Home-stead areas are inundated during extreme high rainfall periods. Mostly for only a few hours, but in rare cases for several days. Improvements can be made by construction of a special flood protection system for the home-stead areas with its own separate water management system, not connected to the rice fields. An improved water management will be a key to make living conditions better in the swamp schemes and will increase the development options. That applies to better rice growth with less toxic conditions and possibilities to plant a second dryland crop. Present poor growth of rice shows in Fe-toxicity, Brown Spot and general toxic, an-aerobe conditions with retarded growth.In some cases also zinc deficiencies are suspected in the rice. Pests are often mentioned as a cause for poor performance, but I consider them not essential in comparison with the physiological rice diseases in Swamps.
A major problem in large schemes is the accumulation of very acid water in canals deep inside the schemes. During rainfall, early in the season, large quantities of iron are released into the canals. These acids often accumulated over years in the canals because the original open canal system can not dispose acid canal water to the rivers deep inside a scheme. By installing gates at appropriate locations and by operating the gates in the one-way flow mode, using the tides for gravity flow, the acids can be gradually released to the main canals and the adjoining rivers. (On the right is a picture of a canal which was a year before still extremely acid, by one-way flow the problem has been solved, the pH is 6 now, note also the remaining oxidized iron.) It is expected that proper water management and knowledge expansion will solve the acidity problems for the future in Indonesian Tidal Swamp Schemes. A new balance will be found between pyrite oxidation and the leaching/flushing capacity of the system. Monitoring of extreme acid soils and canals in Model areas for several years proved this assumption.
A thumbnail of Karang Agung II project (South Sumatra province, World Bank financed, completed in 1991) Landsat ETM+ ,dated 05/07/2000. This project never has been upgraded (Rainfed wetland rice with maize as a second crop, or three times/year maize only) Success related to relatively good soils and a good lay-out and canal design of the Scheme, based on drainage of fields. (no supply option). Note the tree crops vegetation along the main canals with the house-lots. Size of project 30,000 ha. For more rice crops in this project, pump irrigation will be required. Although this project is a major success in swamps development on a large scale, there are also clear problems as has been noted by me in a recent visit to the project. See the photos made during this trip.
Thanks to TRFIC (Tropical Rain Forest Information Center, Basic Science and Remote Sensing Initiative, Michigan State University). See Links for the Website.
According Webhits you are visitor No. since 1 January 2003
Go back to Table of Contents