Scope and speciality of floating agriculture in Bangladesh

Floating agriculture is a way of utilizing areas which are waterlogged for long periods of time in the production of food.  The technology is mainly aimed at adapting to more regular or prolonged flooding. The approach employs beds of rotting vegetation, which act as compost for crop growth. 

These beds are able to float on the surface of the water, thus creating areas of land suitable for agriculture within waterlogged regions.  Scientifically, floating agriculture may be referred to as hydroponics. In Bangladesh, it has regional names such as baira, geto, dhap and bed.

Dhap cultivation is found in remote, waterlogged villages of Barisal, Pirojpur, Satkhira and Gopalgonj districts of Bangladesh, but is not common elsewhere in the country.

According to local tradition, this indigenous system of soilless cultivation' has been used for growing different types of vegetables and seedlings for at least two centuries. The floating beds last for five to six months and then are dragged by country boats, using ropes and hooks, to shallow water to form ridge-type elongated platforms, called kandi.

These are then used as permanent cultivation beds in the wetlands. Dhaps and kandis in our field area are generally 50-60 metres long and 1.2-1.5 metres wide. The thickness of the beds is usually in the range of 25 to 50 cm, with approximately two-thirds submerged.

A space of open water between two dhaps or two kandis is kept clear in order to ply small boats for sowing, weeding and harvesting. Plants derive nutrients mainly from the organic matter but also from any top dressings applied.Various types of local materials are used for building the floating layers.

The single most important component is water hyacinth (Eichhornia crassipes) but 'topapana' (Pista stratiotes), 'son ghash' (Imperata cylindrica), 'noll ghash' (Hamerthria protensa), ash twigs, and dissected coconut fibres are also used. Farmers initially make a layer of water hyacinth and leave it for a few weeks to decompose. When decomposition has started, a 15 cm layer of ash and fibre mixed with sliced topapana is spread on top.

Farmers do not generally use any kind of frame, metallic or otherwise, to support the layer but the integrity of the dhap is important and farmers use their experience to avoid disintegration. Next, seeds are sown in small balls locally known as 'mada'. Madas have two constituent parts and are assembled by women and children.

Initially spherical pots are made by coiling aquatic weeds such as 'del loita' (Amaranthus viridis) and 'khudipana' (Lemna perpusilla), and these are then stuffed with decomposed topapana, which holds moisture, and also sawdust and algae.

Once the madas are ready, they are planted with the sprouting seeds of bottle gourd, country bean, bitter gourd, snake-gourd, cucumber, lady's finger, and placed in the floating beds. The seeds are usually germinated elsewhere but farmers also plant seeds directly on the dhap after spreading a layer of sawdust on the floating platform.

The seedlings are irrigated by hand at first to prevent them from drying out but a few days after sprouting they penetrate through the mada and later the upper, dry portion of the raft. They stay on the dhap until they are sufficiently mature to sell, at a height of about 12-18 cm. This region is one of the main seedling supply zones of Bangladesh.

Various seedlings are grown on the floating beds such as those of chili, water melon, musk melon, different beans, cauliflower, cabbage, radish, tomato, egg plant, bottle gourd, sweet gourd, and turnip.

These seedlings meet a demand that exists throughout the country. Dhaps are used for raising these seedlings but some leafy vegetables, especially spinach, are also grown on kandis, in crop combinations such as the following:
* Potato + Cabbage + Egg Plant + Bitter gourd + White gourd
* Potato + Brinjal + Bitter gourd + Cucumber
*Potato + Cabbage + Brinjal + Bitter gourd + Cucumber
*Onion + Brinjal + Cucumber +Bitter gourd
* Garlic + Chili + White gourd + Bitter gourd
* Tomato + Water Arum + Sweet gourd
* Sugar cane + Tomato + Brinjal + Chili
* Jute and/or 'Dhaincha' (Sesbania aculeata) in the first year only.Floating agriculture can be used in areas where agricultural land is submerged for long periods; the approach is reasonably widespread in Bangladesh where agricultural land is inundated for extended periods during the monsoon season.

A typical example of floating agriculture in Bangladesh involves a floating layer of water hyacinth, straw or rice stubble to which is added upper layers of small and quick-rotting waterworts which make for good manure.

  The structure of the floating raft is strengthened with bamboo, while bamboo poles are used to fix it in position to avoid damage caused by wave action or drifting.  This floating raft can then be transferred to any submerged location for agricultural purposes. 

The practice helps mitigate land loss through flooding, by allowing cultivation of these areas to continue.  In this way, the total cultivatable area can be increased and communities can become more self sufficient.

In addition to this, the area under floating cultivation is up to 10 times more productive than traditionally farmed land and no additional chemical fertilizers or manure is required.  When the crops have been harvested and floating rafts are no longer required, they can be used as organic fertilizers in the fields or incorporated into the following years floating beds as a fertilizer.

The approach uses water hyacinth, a highly invasive weed with prolific growth rates, in a highly beneficial way.  By harvesting water hyacinth, areas covered by the weed are cleared, with the beneficial side-effect of reducing breeding grounds for mosquitoes and improving conditions for open-water fishing by cultivating crops in water, it is also possible to simultaneously harvest fish populations which reside in the beds The practice of floating agriculture also helps supplement the income of local communities and contributes to alleviation of poverty.

 It also provides greater food security by increasing the land output and supporting capacity for poor and landless people.

People practicing floating-bed cultivation are enjoying a better life economically, than those in other flood-affected areas who have not yet adopted this practice. Because the system is fairly labor intensive, it also has the capacity to provide employment opportunities within communities.  As both men and women can carry out the floating agriculture practices, it can also lead to improvements in gender equity.

Floating agriculture is an environmentally-friendly option for increasing the land available for agriculture.  As such, the practice could be sustainable and profitable in developing countries, helping to supplement incomes and to increase food security.

Regular, land-based agriculture requires farmland to be protected behind embankments or reclaimed from estuarine systems.  Both of these activities can have detrimental side effects upon the local environment and economy.  In contrast, floating agriculture can be conducted without land claim and hard defenses.

The procedure can even contribute toward maintaining healthy wetlands which have coastal defense functions and also support a wide range of biodiversity. Aquatic invasive species used in floating agriculture are considered to be the second largest reason for biodiversity loss worldwide.  Clearing waterways to collect these plants is therefore beneficial to the health of wetland ecosystems and may contribute toward maintaining high biodiversity and associated benefits.

At present a joint venture of  DAE and BARI recently launched  a project named Research, Extension and  Popularization of  Vegetables and spices Cultivation on floating Seed  Bed Project over  46 upazila of  22 districts in 8 divisions of DAE  part. Simultaneously BARI part run their project over 25 upazila of 13 districts in 5 Divisions.

The writer is Monitoring & evaluation officer, Research, Extension and Popularization of vegetables and spices cultivation on floating bed project (DAE Part).

--Bibekananda Hira