This paper investigates the impacts of salinity on crop agriculture in south-central coastal zone of Bangladesh, more particularly interior coast. The coastal areas of Bangladesh, with near flat topography and location at the tip of “funnel shaped” Bay of Bengal, are susceptible to a number of natural hazards such as cyclones, tidal surges, salinity intrusion, riverbank erosion, and shoreline recession. The coastal zone of Bangladesh, especially exposed coast has come into focus in a number of policy and academic studies for salinity intrusion, but with the accelerated impacts of climate change salinity extends from the exposed to the interior coast hampering crop production. To investigate extent of salinity level in interior coast and its impact on crop agriculture, this study tested irrigation water collected in between October and December 2011 from the lower Meghna at Gosairhat upazila in Shariatpur district and interviewed experts and local farmers. This study estimated that salinity concentration of surface water was 1.3 dS/m which was 0.8 dS/m higher than the earlier estimation by ICZMP (Integrated Coastal Zone Management Plan) in 2003. The test further revealed that Chloride ion concentration in irrigation water was 500 ppm, pH level was 7.99 and concentration of Carbonate ion was 221 ppm, which were much higher than the desired level. Estimated salinity concentration has already put a threat to the crop production and a significant yield loss has already been noticed in dry season. In the changing scenario of sea level rise, it has been predicted that the increasing concentration of salinity would create more pressure to the farmer by reducing yield on one hand and threatening livelihood, income generation and food security on the other hand. Therefore, to reduce the future loss and prevent the present loss, the study recommends leaching and selecting salinity tolerant crop varieties as adaptation techniques.
Salinity intrusion is a growing problem in the coastal areas around the globe, especially in the low-lying developing countries [
Bangladesh, a low-lying deltaic land, is particularly vulnerable to climate change and its associated hazards [
Coastal area of Bangladesh has already been experiencing erosion. It has been found that the sea level rise of 0.5 m over the last 100 years has eroded approximately 162 km2 of Kutubdia, 147 km2 of Bhola and 117 km2 of Sandwip [
Being an agrarian country, 60% people of Bangladesh are directly or indirectly dependent on agriculture for their livelihood, with the contribution of 20% to its GDP [
CCC [
The rate of salinity intrusion in coastal Bangladesh is faster than it was predicted a decade ago [
Bangladesh is a part of the Bengal Basin, one of the largest geo-synclinals in the world. Comprising an area of 147,570 km2, the country has world’s largest coastline of 710 km, which lies along the Bay of Bengal. About 80% of the country’s land is low-lying floodplains, half of which are subjected to tidal influence, formed through the sedimentation of three large rivers, the Ganges, the Brahmaputra and the Meghna.
The Himalayan range is located to the North and The Bay of Bengal to the South; where the southern coast converges at the northern tip of the Bay of Bengal, like a funnel towards the Meghna estuary. Such geo-physical settings along with abject poverty make the country vulnerable to climate change among which salinity intrusion is the most serious concern for coastal crop agriculture [
In Bangladesh, coastal areas are classified based on proximity to the sea and indicators like tidal movement, salinity and cyclone risk. Depending on the above stated parameter, 133 upazilas (upazila, formerly called thana, is a geographical region in Bangladesh used for administrative or other purposes) of 19 districts have been labeled as coastal upazila, encompassing a land area of 47,201 km2 (32% of total area of the country).
Among the upazilas, 48 from 12 districts face the coast or lower estuary and known as exposed coast and the rest 99 upazilas those are behind the exposed coast are known as interior coast. Exposed coast have already met or crossed the threshold limit of the three parameters. While the interior coast met or cross the threshold limit of two indicators either like, tidal movement and salinity or any one of them, and are usually situated behind the exposed upazila and free from the risk of cyclone [
Based on geomorphologic characteristics, the coastal zone is divided into three distinct coastal regions, namely the western, central and eastern regions. The scope of this study was limited to the South-central coastal zone, situated between the eastern and western region, along the Meghna estuary. Most of the combined flow of the Ganges-Brahamputra-Meghna (GBM) system is discharged through the lower Meghna river estuary which is highly influenced by tidal interactions and consequential backwater effect [
The study was conducted at Panchkathi, Char Bhuinya and Kulchuri Patarchar village of Gosairhat Upazila under Shariatpur district. Among them Panchkathi and Char Bhuinya are under Nolmuri union (smallest local government unit) and the Kulchuri Patarchar is under Kuchaipotti union near the river Jayantia, a branch of the Meghna river (
The District of Shariatpur, geographically known as interior coast, adjacent to the lower Meghna, already met the threshold limit of tidal movement and experienced some sorts of salinity in surface water during dry season and high tide. Withdrawal of water from upstream river system by dam and barrage and rising temperature, decreasing rainfall during dry season and sea level rise due to climate change, have a strong influence over fresh water distribution and tidal penetration which result in salinity intrusion. Salinity intrusion affects fresh water availability into the river systems and therefore, deteriorates usability of drinking and irrigation water. The lower Meghna is subjected to salinity intrusion mainly from decreasing fresh water flow in dry season and hence, saline water penetrates into the river. Generally, a mixture of fresh water and saline water prevails in an estuary. During the dry season, the saline water progresses towards landward more extensively, whereas, it is pushed out towards the bay in wet season. Fresh water input, depends on seasonality, largely has direct impact on salinity distribution along with water circulation and sediment exchange.
Geomorphologic Characteristics of the Study AreaThe study area is located at the old Meghna estuarine flood plain that falls under the coverage of Agro Ecological Zone (AEZ) 19. The land elevation of the study area is medium high and medium low and the soil fall under Debiddar and Burichang category. The pH of Burichang soil class in a medium high land is ranging between 5.9 and 7.0. The organic matter content is medium, which is 2.3%. The average content of Calcium, Magnesium,
Copper, Iron and Manganese is higher, but Boron and Potassium content is low and Phosphorus content is extremely low [
Salinity is increasingly considered as a hazard for the crop production in Gosairhatr upazila, particularly during dry season. The study, therefore, attempts to measure the salinity level, more specifically irrigation water salinity, and its impact on agricultural production. Salinity in river water has diversified impact on socioeconomic factors; however the study deals only with the impact of salinity on crop agriculture in the study area.
The study has employed both qualitative and quantitative approaches to collect and analyze data. Both primary and secondary sources were used to collect data. Primary data were collected in between October and December 2011 through: testing of soil and water samples to measure salinity level, Focus Group Discussion (FGD), Key Informants Interviews (KII), household interviews, and personal observation. Secondary data were collected through assessing a number of scientific and policy studies. Review of secondary literature helps to identify the level of salinity in previous years in different coastal district in Bangladesh and what impacts it have laid on agriculture.
The study intended to explore the salinity level in surface water of the study area, which is mainly used for irrigating agriculture crops. Both physical and chemical properties of water were analyzed in the laboratory of Bangladesh University of Engineering and Technology (BUET). A total of 3 samples were collected, among them two were from the river Jayantia, a branch of the Meghna River, at in-point and out-point of Panchkathi village. The third one is collected from a water body derived from Jayantia River adjacent to Panchkathi village.
The key informants were selected based upon their expertise on the relevant subject matters required for analyzing the issue rigorously. For this study, four key informants interviews were conducted from public (BUET) and private (North South University) universities, GO (SRDI) and local NGO (SDS) respectively. Key informants were interviewed face to face and over telephone using semi-structured questionnaire. Apart from questionnaire, their comments were also taken into consideration.
Using qualitative approach, one FGD was conducted comprising both men and women. Focus group helps to gather a wide range of information in a relatively short time. The participants of the FGD were selected using snowball sampling, comprised of 12 people including subsistence farmer, small landholders and sharecroppers. The rationale behind snowball sampling is to find people with a specific range of knowledge or skill. The participants were asked question regarding climate related hazards, livelihood, agricultural production, income generation, and food security and adaptation technique applied in the locality. The data collected from FGD were crossed checked by the interviewees from different households.
A total of 60 households were interviewed using a pre-tested semi-structured questionnaire to collect information of the farmers who are directly involved in crop production or indirectly involved in agriculture as wage laborer or other agri-activities. Questions were asked regarding impacts of salinity on crop yield, livelihood and health.
The samples were selected using a two-tier approach. In the first tier, firming community was identified with the help of local people and voter list collected from union office. Then, in the second tier, 60 households were selected using techniques of simple random sampling. Farmers in the study area grow different crops whose yield potential is different. However, to estimate the yield loss and decline in crop size, the respondents were asked common questions. Both farmers and wage laborers were asked the same questions regarding affect of salinity in agriculture.
Samples were taken only from three villages that had been used to construct a general scenario for the interior coast, more specifically Shariatpur district. Such small number of sample does not reflect the whole scenario of the interior coast or even the district, but the study could open a new window in climate change research for coastal Bangladesh which demands a more comprehensive study involving multidisciplinary approach.
Water circulation in the coastal zone is largely dependent on the factors like fresh water flow from the river, penetration of tide from the Bay of Bengal and the meteorological conditions like low pressure systems, cyclones, and storms surge and wind [
Rising temperature and fluctuation in precipitation are considered as the drivers of climate change which are
likely to have multiple impacts on the coastal zone of Bangladesh [
Precipitation pattern is likely to change in the South Asia due to higher temperature that results in stronger monsoon circulation [
Bangladesh is highly vulnerable to sea level rise [
Sea level rise has direct influence on salinity intrusion in landward. Shamsuddoha and Chowdhury [
The coastal zone and offshore island in Bangladesh are very flat with height less than 3 m above the Mean Sea Level (MSL). The astronomical tide, therefore, with higher range penetrates landward very frequently. Moreover, intensity and frequency of tropical cyclone and associated storm surge has increased many folds recently due to climate change [
Another natural factor of increasing salinity at coastline is back water effect that takes place at the mouth of the river when fresh water is not sufficient enough to counterpart tide water moving towards river from sea. Ali [
Bangladesh is formed at the confluence of the three mighty rivers: Ganges, Brahmaputra and Meghna (GBM). The basins of three river systems with an area of 1.6 million km2 passing through India, China, Nepal, Bhutan and Bangladesh, drain to the Bay of Bengal through the Meghna estuary. Different types of anthropogenic interventions in the form of dam, barrage, and water diversion channel are established on these river basins by the sharing countries. Thus water withdrawal or diversion of river water at upstream creates a low flow condition in the downstream during the dry season. Alongside faulty management of coastal polders also accelerates inland salinity ingression.
The highest contributor of fresh water to the lower Meghna is the Padma River, the combined flow of Ganges and Brahmaputra (Jamuna), which provides 90% of total fresh water [
Coastal polders were built to prevent tidal intrusion aiming to boost agricultural production. However, [
Salinity in aquatic ecosystem is determined by the total amount of dissolved salts present in it. Four types of cations prevail in saline water such as Sodium (Na+), Potassium (K+), Calcium (Ca++) and Magnesium (Mg++) and 3 anions such as Chloride (Cl−), Carbonate
This study measured EC of irrigation water samples to determine salinity level. The salinity has been measured in micro Siemens per cm (μS/cm) at 25˚C. The EC of irrigation water in the study area was found as 1305 μS/cm or 0.72 ppt at 25˚C. On the other hand soil salinity in the study area has been measured as <4 dS/m [
Salinity intrusion in river water may cause economic loss in terms of crop yield reduction, hampering industrial production, increasing health hazard and reducing productivity of the forest species [
River water with high level of salinity, when used for drinking purpose, may have numerous impacts on human health and livestock. Khan et al. [
Salinity affected irrigation water has profound impact on crop production (
To investigate suitability of irrigation water of the study area, parameters of the samples were then compared with standard level as set by US based soil conditioners supplier Soil First Consulting [
1) Osmotic effect
The most common response of plant towards salinity is reduction in growth. In low to moderate concentration, salinity affects crop production by lowering the soil-water potential and increases concentration of salt at the root zone. Low water potential indicates that plant cannot extract sufficient amount of water from soil and maintain turgor at very low soil-water condition. This effect is known as osmotic effect. Bauder et al. [
Parameter | Standard level [ | Present level (in the study area from the empirical study) |
---|---|---|
pH | 5.5 - 6.0 is the ideal condition for both irrigation and tank mixing; >7.0 can cause problems, especially in tank mixing | 7.99 |
Salinity or concentration of salt | 1.5 dS/m | 1.305 dS/m |
Alkalinity (carbonate) | <50 ppm | 221 ppm |
Chloride ion | <140 ppm | 500 ppm |
Sodium ion | 0 - 50 ppm | _ |
The current study has found that EC of the irrigation water is 1.305 dS/m which is slightly saline according to FAO (1992) guideline and moderately saline according to FAO (1976) guideline, whereas highly saline according to USDA (1954), cited in [
2) Ion effect
Excessive presence of ions like Na and Cl in irrigation water may cause toxic effects in plant growth. The toxic effects caused by specific ions may occur either when the ions are taken up by the root or when gets the direct contact with the leaves.
Even though Cl is an essential element for plant growth, but higher concentration may restrain plant growth or cause toxicity to some plants. Irrigation water with high Cl content is likely to reduce the availability of phosphorus to plants. Higher concentration of Cl ions also causes leaf tip burn, disruption of membrane function, obstruction in internal solute balance that hampers nutrient uptake [
3) Direct foliar adsorption
Some plants may not be responsive to root uptake of toxic ions like Na or Cl ion, however may be sensitive and build up symptoms when come in contact directly with the ions. The toxicity of Cl ions and Na ions due to adsorption is visible when irrigation is carried through sprinkler method. This toxic effect causes foliar damage of some specific crops in terms of scalding or burning the leaves coming in contact with the specific ions. Damage caused by direct contacts of ions gets more severe when irrigation takes place in a hot and dry weather [
The current study found that the Cl ion content in irrigation water is much higher than the desired level. Even though Na ion concentration of irrigation water in the study area has not been estimated under the current study, it can be predicted that the concentration of Na ion would also be higher as that of Cl ion is higher. The farmers of the study area claimed that they have been experiencing some of the impacts of salinity such as early yellowing of leaves, burning leave tip, early aging of plant which might create dropping down of leaves in premature stage and therefore, reduce the rate of photosynthesis.
4) pH, alkalinity and nutrient deficiency
Bauder et al. [
EC of water in dS/m (=mS/cm) | |||
---|---|---|---|
Classification | USDA (1954) | FAO (1976) | FAO (1992) |
Non-saline | <0.25 | <0.75 | <0.7 |
Slightly saline | 0.7 - 2.0 | ||
Moderately saline | 0.25 - 0.75 | 0.75 - 3.0 | 2 - 10 |
Highly saline | 0.75 - 2.25 | >3.0 | 10 - 25 |
Very high saline | 2.25 - 50 | 25 - 45 | |
Sea water: >45 dS/m |
ions as the dominant in the solution. Higher alkalinity in irrigation water reduces micro nutrient availability as well [
The study measured pH level as 7.99 and concentration of CO3 ion as 221 ppm, which is much higher than the desired level. Higher concentration of CO3 ion in irrigation water results in increased concentration of Na ions in the root zone. Photosynthesis, thereby, may be hampered if Na ion concentrates in the stomata of leaves.
Agriculture is the main source of livelihood for people of Gosairhat upazila. Among the interviewee households, sharecropper appeared as the highest number and most of them grow Boro rice in dry season. They also grow wheat, some tuber crops, vegetables, pulses, oil seeds and spices in dry season.
Local people’s perception reveals that salinity intrusion is an increasing hazard to agriculture in dry season. Among the respondents, 72% opined that salinity has become the most prevalent hazard for their crop production during the dry season. Even they could test saline in their drinking water collected from shallow tube wells. They argued that crop production has been declining for last 5 - 6 years. Majority of the respondents (78%) agreed that salinity intruded to their land when they used water from their adjacent rivers such as the lower Meghna and Jayantia River during high tide. However, 8% respondents believed that manmade hazards like emission from brickfield could have significant impacts on the reduction of crop yield in their locality. Water scarcity was identified as hazard by 4% of the respondents and argued that they have been facing fresh water crisis both for drinking and irrigation because of the presence of salinity.
The result shows that impact of salinity on crop production is visible in the study area. Most of the respondents (92%) in the study area claimed that they have been experiencing yield reduction (
The most pressing problem faced by the farmers in the study area is yield loss. However, the yield loss is not uniform for all food crops.
Different crops respond to salinity differently even at a same level. Based on yield potentiality, [
By calculating the yield potentiality of different winter crops in the study area and comparing them with that of the standard yield potentiality as proposed by [
Crop | % in yield reduction based on different soil salinity (EC in dS/m) [ | Yield potential (%) proposed by [ | Yield potential (%) measured for field crops | ||
---|---|---|---|---|---|
0% | 10% | 25% | 0% | 3.5% | |
Onion | 1.2 | 1.8 | 2.8 | 72 | 66.67 |
Beans | 1.0 | 1.5 | 2.3 | 66.67 | --- |
Potato | 1.7 | 2.5 | 3.8 | 80.56 | 77.78 |
Sweet potato | 1.5 | 2.4 | 3.8 | 79.2 | 78.57 |
Carrot | 1.0 | 1.7 | 2.8 | 70.58 | |
Radish | 1.2 | 2.0 | 3.1 | 74.7 | 74.04 |
Pepper | 1.5 | 2.2 | 3.3 | --- | ---- |
The formula of yield potentiality was developed by Grattan (2002) that has been applied to estimate the yield potentiality in this study. The formula is % yield = 100 − b (ECe − a) [Where a = threshold limit, b = percent of yield loss with the increase in one unit of salinity above the threshold limit, ECe: Average soil salinity in the root zone]. Threshold value is the value of soil salinity level at which plants start experiencing the impact of salinity in terms of yield loss.
potentiality in the study area compared to the standard yield potentiality (
The study finds that the vegetable crops are more sensitive to the present level of salinity than the cereal crop (
Crop | Yield loss (kg/decimal) | No loss | |||
---|---|---|---|---|---|
Boro | 1 (12) | 2 (15) | 5 (4) | ---- | (29) |
Wheat | 2 (18) | 5 (10) | --- | ---- | (32) |
Potato | 4 (12) | 5 (15) | 8 (7) | 10 (21) | (5) |
Mustard seed | 2 (19) | 4 (10) | 5 (25) | ---- | (6) |
Sweet potato | 3 (17) | 4 (14) | 6 (3) | 7.5 (21) | (5) |
Amaranth | 1 (25) | 2 (19) | --- | --- | (16) |
Lentil | 2 (14) | 3 (9) | 4 (18) | 6 (7) | (12) |
Radish | 3 (12) | 5 (15) | 7 (26) | ---- | (7) |
Chili | 2 (12) | 3 (19) | 5 (14) | 6 (8) | (7) |
Onion | 2 (10) | 2.5 (19) | 4 (22) | --- | (9) |
Grass pea | 3 (15) | 5 (18) | 6 (10) | ---- | (17) |
factors like type of the soil, slope of the field, method of irrigation, management of salinity, timing of irrigation, fertilizer and manure practice.
Moderate to low level of salinity could be managed through leaching process either naturally or artificially. Naturally, rainfall contributes to leach salt from soil surface but in dry season, when rainfall is insufficient, the artificial process or irrigation should be applied. To manage salinity, more water needs to be applied other than regular water requirement of the crop. However, there is a high risk of increasing salinity content at root zone in case of irrigation with saline contaminated water. Deep-water irrigation is required in case of high concentration of salinity in root zone. If soil salinity is too high comparing to the desired level of a certain vegetable in its root zone and the root is 30 cm depth, 15 cm of water is capable of leaching salinity by 50% and 30 cm of water is capable of leaching salinity by 80% and 60 cm by approximately 90% [
Irrigation method and adequate drainage also influence soil salinity. Irrigation water, containing various dissolved minerals, has a great influence on crop production as well as on soil salinity management. Nevertheless, minerals or salts and their concentration as well as composition vary largely depending on the source of irrigation water. Simple surface water run-off cannot leach soil salinity; rather water should be drained through soil. Therefore, deep tillage is required to ensure internal drainage as it is very important to break up the restraining layer that delays water movement. In this regard, sprinkler irrigation provides a better control of water application rates. In plain land flood irrigation can also be used as an effective tool for controlling salinity.
Surface water is the principal source of irrigation water in the study area. EC of the irrigation water in the study area has been estimated as 1.3 dS/m, leaching is highly recommended for the study area especially during winter. To calculate the leaching requirement for different winter crops, FAO [
[In Equation (1), LR = the minimum leaching requirement needed to control salts within the tolerance (ECe) of the crop with the ordinary surface method of irrigation, ECw = Salinity of the applied irrigation water in dS/m and ECe = average soil salinity tolerated by the crop as measured on a soil saturation extract.]
Leaching fraction is a percentage of water that needs to be applied in the field so that it can drain the root zone3. Applying the Equation (1), leaching requirement of some major winter crops of the study area are estimated (
Leaching requirement of different crops varies according to their threshold limit as well as percent of yield that a producer desires. The more percent of yield a producer desires, the more leaching is required. Therefore,
Crop | Leaching requirements for 100% yield potential | Leaching requirements for 90% yield potential |
---|---|---|
Onion | 0.27 | 0.168 |
Beans | 0.35 | 0.20 |
Potato | 0.18 | 0.116 |
Sweet potato | 0.209 | 0.12 |
Carrot | 0.35 | 0.18 |
Radish | 0.27 | 0.149 |
Grattan (2002) defined the leaching process as “Leaching is the process of applying more water to the field than can be held by the soil in the crop root zone such that the excess water drains below the root system, carrying salts in it.”
salt tolerance values of different crops of a certain geographic area should be used as a guide for the farmer to choose what crop they should produce to have the optimal production considering physical condition of an area. In the study area, neither the agricultural office nor the farmers are informed about the salt tolerance limit nor do they have any chart.
The exposed coast and some areas of the interior coast in Bangladesh have already exceeded the threshold limit of tidal movement and salinity intrusion [
The study area experiences salinity due to tidewater movements in different canals of the lower Meghna that crosses the upazila. Moreover, higher rate of evaporation from soil also contributes to increasing salt concentration in soil. Therefore, salinity problem becomes acute in hot and dry season than that of wet season. Furthermore, a trend of decreasing rainfall in winter has already been predicted [
Present salinity concentration has already put a threat to the crop production and a significant yield loss has already been observed in the dry season. In the changing scenario of the sea level rise, it has been predicted that increasing concentration of salinity will create more pressure to the farmer by reducing yield which will ultimately affect livelihood, income generation and food security.
Leaching and irrigation time are considered as useful tools for managing low to moderate level salinity. Crops with a higher threshold value are likely to have lower leaching requirements and therefore, will require a less amount of irrigation water. On the contrary, low tolerance value requires high leaching that means more water is needed to increase the yield potentiality which will incur high production cost. Moreover, salinity in irrigation water also influences the soil salinity and pH. Higher pH in soil is likely to create a deficiency of nutrient like phosphorus, iron etc. To reclaim the nutrients, appropriate fertilizer should be applied against the deficiency of certain nutrient. For instance, to address the deficiency disease named “Lime-induced Chlorosis”, an Iron deficiency disease, Iron sulphate needs to be applied in the soil [
This study was conducted under RESOLVE project, jointly implemented by Unnayan Onneshan and Oxfam Novib. The Authors wish to thank Dr. Rashed Al Mahmud Titumir for his scholarly and mental support through- out the study and preparing the manuscript. Also thanks to SDS (Shariatpur Development Society) for their immense logistic and technical support during field data collection. A draft version of the preliminary study report was uploaded in the Unnayan Onneshan website (www.unnayan.org) for comment.