Soil status in Bangladesh

| Updated: October 25, 2017 02:16:11

Soil status in Bangladesh

Funded by the Department for International Development (DFID) of the UK, the Research and the Evaluation Division (RED) of BRAC conducted a diagnostic study on agricultural sector of Bangladesh.  Reviewing the last four decades of progress and problems, the main purpose of the study was to build a future drawing upon the past.
Soil fertility is alleged to be threatened in the wake of many developments. Agro ecological zones and sub-zones are very broad units. Fertility status and agricultural productivity of these regions vary considerably. Individual farmers have fragmented  lands into small pieces causing wide variation in the management of each and every piece of land. This leads to large variation in fertility levels even between adjacent plots.
Although Bangladesh is a small country, it has a wide variety of soils. Its fertility status is extremely variable. Most of the soils are depleted and in urgent need of replenishment with manures and fertiliser if productivity has to be enhanced. It is estimated that more than 100 kg nutrients per ha a year are getting out of the soil system.
Bangladesh also has wide variety and complexity of soils at short distances due to a diverse nature of physiographic condition, parent materials, lands, and hydrology and drainage conditions. Due to intensive cropping to grow more food, continuous changes are taking place in the soil fertility status due to organic matter depletion, nutrient deficiencies, drainage impedance/water logging followed by degradation of physical and chemical properties of soil as well as salinity/acidity.
Nitrogen deficiency in soils implies that all  agricultural soils are critically deficient in soil nitrogen content and deficiency of micro nutrients are also limiting crop production. But the extent of deficiency varies geographically depending on the extent of land use and nature of parent materials. The main reasons for such deficiency are, for example, intense decomposition of organic matter and rapid removal of mineralised products under high leaching conditions and crop removal. Nitrogen, being the most important nutrient element in soils, plays the most vital role in crop production in Bangladesh.
Responses of modern rice to applied nitrogen have been studied extensively throughout the country by a series of fertility trials. The average yield increase due to fertiliser varies from 30 to 75 per cent. In some cases, without application of nitrogen fertilizer, modern rice showed almost complete failure while application of 100 kg N/ha along with other nutrients resulted in a very successful crop yielding 6-7 t/ha.
Phosphorus is the second most important nutrient element limiting successful crop production. It becomes unavailable or fixed in soils through a variety of ways. In acidic terrace and brown hill soils, phosphorus is largely fixed by iron and aluminum oxides at low pH, while in calcareous soils fixation occurs by calcium-magnesium carbonates. The net result of fixation is a decrease in the immediate availability of native and applied phosphorus.
Potassium is the third major plant nutrient recently identified as deficient in most Bangladesh soils. The previous idea about sufficiency of potassium in soils might be true for local crop varieties with low yield potentials. One-ton wheat/ha or 2-ton rice/ha can be obtained from soils where K would be a limiting factor continuously without K fertilisers. The crop intensification with high-yielding and hybrid varieties has shown widespread deficiency of potassium in Bangladesh soils. It has been recorded that a 5 ton/ha rice crop will remove more than 110 kg K which is to be made available to plants in less than 3 months' time and many of our old and highly weathered soils may not have potential to supply K at this rate.
Sulphur has been recognised as the fourth major nutrient limiting crop production as early as in 1980. In the past, very little attention was paid to this nutrient until 1977 when sulphur deficiency in wetland rice was first detected at the Bangladesh Rice Research Institute (BRRI) farm and in nearby farmers' fields. Since then, sulphur deficiency in Bangladesh soils is becoming widespread and acute. It has been reported that variable amount of available S in soil ranging from as low as 2?g g-1 soil to as high as 75 mg g-1 is available. The use of fertilisers such as urea, triple super phosphate, muriate of potash and diammonium phosphate, cultivation of modern varieties, increasing cropping intensities and limited application of organic manure have all contributed to intensification of the S deficiency problem in Bangladesh soils. The problem is more severe in wetland rice than in upland crops as anaerobic condition, under which rice is grown, reduces sulphate and makes it unavailable to plants.
 Soil degradation is common in Bangladesh, whether manmade (for example, through unbalanced use of fertilisers) or due to natural factors (salinity ingress in coastal areas, or landslides on hilly terrain). Estimates by the BARC indicate that problem soils may be major constraint to agricultural growth. Organic matter depletion is observed in 7.5 million ha of land. Declining soil fertility, soil erosion, and salinisation affect respectively 5.6-8.7 million ha, 5.3 million ha, and 3.05 million ha of land.
Saline intrusion from sea water in coastal areas, compounded by tidal surges, adversely affects life, property, ecology and agricultural production in those areas. The problem is intensified with global climate change effect and degrading more areas with salinity.  One study mentioning SRDI data showed that over 103,000 ha of lands were saline in 2000, which is about 20 per cent more than the saline area in 1973. This indicates that saline areas have been increasing in the country over the three decades and will continue in the coming years with sea level rise due to climate change. During the monsoon, about 12 per cent of the total area is under high salinity levels which increase to 29 per cent during dry season. The increased salinity level would limit cultivation of many crops in coastal areas.
 It is estimated that some 2.0 million metric tons of nutrients are removed from Bangladesh soils annually. Unless compensated through balanced application of nutrients every year, the fertility of land is expected to decline and so will its productivity. One estimate puts the cost of land degradation at 3 per cent of crop output or 1.0 per cent of crop GDP every year.
Apart from the natural factors, a major reason is unbalanced use of fertiliser-a reflection of the historical legacy of low relative price of urea compared to non-urea fertilisers. Pricing policy, as along with investments in awareness-raising for balanced fertiliser application and popularisation of more efficient fertiliser application techniques, can help preserve soil quality, raise output, lower costs of production, and save huge amounts of government money.
Abdul Bayes is a Professor of Economics at Jahangirnanagr University.
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