Acreage of high yielding varieties of rice has increased in the last three decades, replacing hundreds of local varieties.
HYVs and other modern rice varieties are now grown on 85 percent of land under gross cultivation area of rice a year, which was 32 percent in fiscal 1987-88 -- a transformation that has raised the country's rice output.
Modern rice varieties now account for 99 percent of boro areas, 73 percent of aman areas and 80 percent of aus areas.
Improved varieties including hybrids accounted for 92 percent share of the 3.47 crore tonnes of rice produced in fiscal 2015-16, up from 50 percent of total rice output nearly three decades ago, according to Bangladesh Bureau of Statistics.
But agronomists said HYVs and other modern varieties are unlikely to be grown exclusively because of various factors like submergence of land under water, salinity and farmers' interest in some local varieties.
So, modern rice, including hybrid, is not going to fully replace indigenous rice varieties in the near term, according to agronomists.
“It is very difficult to cover the rest 1 percent of boro area with HYVs,” said Md Ansar Ali, director for research at Bangladesh Rice Research Institute (BRRI).
This is because most of the areas are in the deepest part of the haor or ditches where mostly local boro or Habiganj boro is cultivated to escape flash floods, he added.
Scientists and agricultural workers said HYV coverage will rise further in the aman season, from 73 percent at present. But the share of the improved rice varieties in aman may not exceed 90 percent of the total area, they added. Wais Kabir, former executive chairman of Bangladesh Agricultural Research Council (BARC), said the rising acreage of HYVs was expected.
But HYVs cannot be grown in some parts of the south where tidal waters do not recede and the lands remain submerged, he added. “In those areas, there is no alternative to local varieties.”
However, the recently introduced varieties like BRRI Dhan-76 and 77 have given hope that these areas can be brought under HYV cultivation.
Agriculturists said a portion of land in the southern region is either low-lying or contains standing water. And HYVs, seedlings of which can grow fast by tolerating standing water, are needed for such areas during aman season.
But there is a dearth of HYVs that are suitable for cultivation on lands under water.
Khairul Bashar, a breeder and former director of BRRI, said 30 percent of area in the south is either low-lying or contains standing water. Long seedlings are needed for cultivation in the aman season in those areas. Currently, such HYVs are inadequate, he added.
Bashar, also the country manager of Harvest Plus, an NGO, said varieties that can tolerate multiple stresses -- salinity and submergence -- should be developed for the southern region.
BRRI's Ali said BRRI Dhan-76 and 77 have longer seedlings like local varieties such as Sadamota, Dudkolom, Khayamota and Kalomota, which are appropriate for the central southern region.
Md Hamidur Rahman, the immediate past director general of the Department of Agricultural Extension, said there are some preferred local varieties of aman among farmers in the south. “Those are very stress-tolerant.”
The newly developed HYVs -- BRRI Dhan-76, 77 and 78 -- which have the strength to withstand tidal water, submergence and salinity may make some breakthrough for expansion of HYV acreage during the aman season, he said. “Demonstration of these varieties will start this year. Performance of the varieties will be clear within the next couple of years.”
Salt-tolerant HYVs can be expanded during boro season in the southern area, where sweet water remains available until May, the month of Boro harvest, said Ali of BRRI.
More than 10 lakh hectares of land remains fallow during the boro season in the greater Barisal region, he added.
Ali said 139 polders exist across the coastal region. In each polder, there are many canals and dead rivers.
These can be used as sweet water reservoirs by harvesting rain water for the cultivation of boro or other winter crops, he said, adding that re-excavation of the canals and rivers might be required.
“Above all, policy support and political will are also required in order to avoid a conflict of interest,” Ali said.
Kabir said the expansion of boro cultivation will depend on water management, particularly in the southwest and south-central regions.