Twenty soil samples are collected from two disaster-prone coastal unions of Kaliganj Upazilla under Satkhira District with an aim to study the soil properties in relation to the time series data as well as to evaluate the overall impacts on agriculture. Results revealed that the soil physical parameters such as field moisture, hygroscopic moisture and soil textural classes are favourable for agricultural crop production but chemical parameters such as soil pH, soil salinity, organic matter, total nitrogen, CEC etc. are not in optimum range. In regard to electrical conductivity, most of the soils with study area showed slight to medium salinity which may hamper agricultural production. PH of most of the soils are in alkaline range which delinquent for nutrient supply that affects crop growth and agricultural production. Organic matter contents are also decreased as compared with the series data. The reasons of these deplorable conditions might be frequent natural digesters, shrimp culture, crab culture, salinity intrusion, drought, flood and tidal surges etc. in the study area. Therefore immediate steps should be taken to adapt these situations. Otherwise future agricultural production will be affected to a great extent in the area under investigation.
The Asia-Pacific region is one of the most disaster-prone regions in the world accounting for over 60 per cent of world’s disaster events (EM-DAT, 2008). Bangladesh often suffers from many climate induced disasters such as flood, drought, and cyclone. Among those natural hazards, cyclone is a tropical storm or atmospheric turbulence involving circular motion of winds, occurs in Bangladesh almost every year. Mainly cyclones in 1970, 1985, 1991, 1997 and 2007 resulted lots of death. On 15 November 2007, Cyclone Sidr, a category-4 storm struck the coast of Bangladesh and moved inland, destroying infrastructure, causing numerous deaths, disrupting economic activities, and affecting social conditions, especially in the poorer areas of the country. In latest on May 25, 2009 the cyclone Aila had hit the south-western part of Bangladesh and caused 325 deaths (Roy et al, 2009), affected the residents, homesteads, roads and embankments. In total, over 3.9 people were affected (UN, 2010) and nearly 350,000 acres of crop land were destroyed. The cyclones also move towards the eastern coast of India, towards Myanmar and occasionally into Sri Lanka. But they cause the maximum damage when they come into Bangladesh, west Bengal and Orissa of India. This is because of the low flat terrain, high density of population and poorly built houses.
Most marginalized communities living in remote villages along Bangladesh’s coastal zone are exposed to a number of climatic induced hazards. Salinity intrusion has been a typical environmental issue for these disaster prone areas in our country; it is the single most significant problem in south-west coastal regions of Bangladesh. It changes the pedological properties of soil. For this reason, the south-west coastal regions of Bangladesh are food deficit area. In recent past observations, it is noticed that due to increasing degree of salinity and expansion of affected areas normal agricultural land use practices become more restricted (Karim et al, 1990). The salinity affected areas of Bangladesh are still increasing rapidly (SRDI, 2010). In the recent past two devastating cyclones and storms induced a change in the level of salinity in south-western regions leading to normal crop production conditions. Thus, crop yields, cropping intensity, production levels since then decreased much more than other part of the country (Rahman and Ahsan, 2001). It is mentioned in the daily and weekly that due to the cyclones and storm surges, floods, damage of embankment by intrusion of saline water to the inland is a common phenomenon at the coastal belt area. This scenario prevails for longer time, subsequently use of land in agriculture sector will substantially reduce, and as a result, the ultimate impact will increase the vulnerability of the coastal region people especially in Kaliganj Upazila which is located at 22°27’00”N-89°02’30”E known as disaster prone area under Satkhira district in Khulna division. Two unions (Ratanpur and Dhalbaria) were selected for detailed study to assess soil properties of these areas. These areas were affected by most of the natural disasters in the past.
1.2: Objectives of the Study
The main objectives of this study are-
- To observe the present soil properties in the study area
- To detect the changes of soil properties in the study area
- To evaluate the impact of natural disasters on agriculture of the study area
MATERIALS AND METHODS
3.1: Selection of Study Area
The study area is the two unions of Kaligonj upazila under Satkhira district (Figure-3.1). Kaliganj is south-west coastal region of Bangladesh which is a disaster-prone area. The natural disasters often devastate this area. The peoples of that area are in vulnerable to natural disasters. Therefore this site was selected to study which is located at 22°27’00”N-89°02’30”E in Khulna division. This area is the hub of all types of silent disasters like cyclones, Aila in 2009, Sidr in 2007, tidal surges, floods, drought, salinity intrusions, repeated water logging and land subsidence. Therefore, this region is thought to be the most disaster-prone region in Bangladesh and highly vulnerable to the effects of climate change. It covers an area of 333.8 km2. It has 12 unions and 272 villages. Total population is 2,73,420 persons in which male is 1,35,742 persons and female is 137678 persons. The density of population is 676/km2. Approximately 85% of the people of this region depend on agriculture. Fishing, shrimp farming, salt farming and tourism are the main stream of economic activities. The south-western region experiences extreme inland saline-water intrusions and agricultural crop fields gradually experiences salinity increase.
3.2: Data Collection
This research utilized both quantitative and qualitative data collection methods to explore current and potential future climate change impacts on Kaliganj Upazila in Satkhira, south-west Bangladesh. It is based on both the primary and secondary data and other records and information.
Figure-3.1: General map of Kaligonj Upazila of Satkhiradistrict showing the sample sites (inset: Map of Bangladesh)
3.2.1: Primary Data Collection
Collection of soil samples from the field and analysis of collected samples in the laboratory is the main source of primary data and information. The field survey conducted from 26 March, 2014 to 30 March, 2014. It was done by collection of 20 different soil samples from the two unions of Kaliganj Upazila under Satkhira district. This Upazila was affected by natural disasters like Aila, Sidr etc. Co-ordinate points of collected samples are given in Table-3.1.
3.2.2: Secondary Data Collection
Some general information was collected from agricultural field office situated at Kaligonj Upazila in Satkhira district through personal communication, farmers and local people who are engaged with agriculture. Table-3.2 shows some general information about Kaliganj Upazilla. Published materials, books, journals and different organization reports are the main sources of secondary information. A structured interview schedule was prepared to collect the required information and data. Moreover, questionnaire survey and face to face interview were done for collecting field level data and information.
3.3: Data Obtained From Laboratory
3.3.1: Soil Sample Preparation and Lab Analysis
The surface soil samples were collected from field. Each of the collected soil samples were dried in the air by spreading on separate sheet of papers after it was transported to the laboratory. For hastening the drying it was exposed to sunlight. They were then grounded by a wooden grinder and passed through a 2mm sieve.
Table-3.1: Soil Series, Land Type, Co-ordinate points of sampling site
|Sample No.||Soil Series||Land Type||Co-ordinate Points|
|Ratanpur-1||Barisal||Medium High Land||22023’59”N||89002’00”E|
|Ratanpur-2||Barisal||Medium High Land||22023’54”N||89002’00”E|
|Ratanpur-3||Barisal||Medium High Land||22023’27”N||89001’81”E|
|Ratanpur-4||Barisal||Medium High Land||22023’24”N||89001’85”E|
|Ratanpur-5||Barisal||Medium High Land||22023’31’N||89001’49”E|
|Ratanpur-6||Barisal||Medium High Land||22023’29”N||89001’47”E|
|Ratanpur-7||Barisal||Medium High Land||22023’22”N||89001’35”E|
|Ratanpur-8||Barisal||Medium High Land||22023’24”N||89001’32”E|
|Ratanpur-9||Sara||High Land||22 23’03”N||89001’28”E|
|Ratanpur-10||Barisal||Medium High Land||22022’90”N||89001’28”E|
|Dhalbaria-1||Barisal||Medium High Land||22022’76”N||89001’30”E|
|Dhalbaria-2||Barisal||Medium High Land||22022’73”N||89001’39”E|
|Dhalbaria-3||Jhalokathi||Medium High Land||22022’50”N||89001’27”E|
|Dhalbaria-4||Barisal||Medium High Land||22022’52”N||89001’28”E|
|Dhalbaria-5||Barisal||Medium High Land||22022’42”N||89001’27”E|
|Dhalbaria-6||Barisal||Medium High Land||22022’42”N||89001’28”E|
|Dhalbaria-7||Jhalokathi||Medium High Land||22022’31”N||89001’32”E|
|Dhalbaria-8||Barisal||Medium High Land||22022’29”N||89001’31”E|
|Dhalbaria-9||Darshana||Medium High Land||22022’34”N||89001’31”E|
|Dhalbaria-10||Barisal||Medium High Land||22022’31”N||89001’35”E|
HL= High land, MHL= Medium high land
The sieved soil were then preserved in plastic container and labelled property showing the depth, sample number and date of collection. The labelled soil samples are stored in laboratory for physical and chemical analysis.
Table-3.2: General information about Kaligonj Upazila (2012-13)
|Total area||333.79 km2|
|Non cultivable land||9757(ha)|
|Roads and other settlements||4157(ha)|
|Neat crop land||23421(ha)|
|single crop land||10440(ha)|
|Double crop land||6986(ha)|
|Triple crop land||5995(ha)|
|Total cropping land||42397(ha)|
|Density of cropping land||70.59%|
|Medium high land||5704(ha)|
|Demand of food||54916 metric ton|
|Production of food||71426 metric ton|
|Using compost fertilizer||815(ha)|
(Source: personal communication*)
*Personal communication with upazila agricultural office of Kaligonj Upazila
126.96.36.199: Physical Analysis of Soil
Field Moisture Percentage
The percentage of moisture present in the soils at field condition was determined by drying known amount of soil in an electrical oven at 1050 for 24 hours until constant weight was detained and the moisture percentage was calculated from the loss of moisture from the sample as described by Black (1965).
Hygroscopic Moisture Percentage
The hygroscopic moisture in air dried soil was determined by drying a known amount of soil in an electric oven at 1050C for 24 hours till a constant weigh was determined. The moisture percentage was calculated from the loss of moisture from the sample (Black, 1965).
Particle Size Analysis
The particle size distribution of soil was done by Bouyoucos hydrometer method as described by Piper (1950). The textural class was determined from triangular co-ordinates as devised by the United States Department of Agriculture (USDA, 1951).
188.8.131.52: Chemical analysis of soil
Soil Reaction (pH)
The pH of the soil was measured electrochemically using a Corning Glass Electrode pH meter (Model-7). The ratio of soil to water was 1:2.5 suggested by Jackson (1962).
Electrical conductivity was measured of the soil at a soil-water ratio of 1:2 by EC meter as described by USSL staff (1954).
Soil Organic Carbon
Soil organic carbon was determined volumetrically by wet-oxidation method of Walkley and Black as described by Piper (1950) and Jackson (1962).
Soil Organic Matter
The organic matter content of the soil was determined by multiplying the percentage of organic carbon, with conventional Van-Bemmelen’s factor of 1.724 (Piper, 1950).
The total nitrogen of the soil was determined by Micro Kjeldhal method following H2SO4 acid digestion as suggested by Jackson (1962).
The C/N ratio of the soil was calculated by dividing the percentage of total carbon by the percentage of total nitrogen.
Cation Exchange Capacity
Cation exchange capacity of the soil was determined by extracting the soil with neutral normal ammonium acetate solution following the replacing ammonium in exchange complex by 2M NaCl (pH-7). The displaced ammonium was distilled with 40% NaOH and ammonium evolved was absorbed in 2% boric acid containing mixed indicator. The absorbed ammonium was titrated with a standard N/10 H2SO4 acid (Black, 1965).
Exchangeable K, Na, Ca, Mg
The exchangeable cations of soil were extracted with neutral normal ammonium acetate solution (NH4OAC) as described by Piper (1950) and Jackson (1962). The extract was analysed for Na and K by Gallenkamp Flame Photometer at 589 and 767 nm respectively, and for calcium and magnesium by Atomic Absorption Spectrophotometer (Perkin-Elmer,3310) at 422.7 and 285.5 nm respectively, (Jackson, 1962).
Exchangeable Na Percentage (ESP)
ESP is calculated by dividing exchangeable Na by the CEC value of soil multiplied by 100 as described by Brady (2004).
Result and Discussion
4.1: Soil Physical Parameters
4.1.1: Field Moisture
Soil field moisture is the moisture existing in the soil at field level. Analytical results of field moisture of the samples are represented in figure (Figure-4.1). The highest field moisture percentage was 19.07% in the study site which co-ordinate point was 22022’529”N and 89001’28”E. This soil sample was collected from Dhalbaria-4. The lowest field moisture percentage was 11.92% in the study site which co-ordinate point was 22022’34”N and 89001’31”E. This soil sample was collected from Dhalbaria-9.
The average value of field moisture percentage was 14.71%. Plants respond favourably to relatively high soil moisture conditions, and the statement is sometimes made that plant growth diminishes progressively as the soil moisture content falls below field capacity and ceases at the permanent wilting percentage (Hagan, 1955).
The behaviour of soil water is most closely related to the energy status of the water, not to the amount of water in a soil. Thus, a clay loam soil will easily supply water to the plant when potential is -10kpa (Brady, 2004).
Burrows and Kirkham (1958) observed variation in field moisture percentage values with variation in texture of different soil. He stated that increase of percentage of field moisture capacity of the soils attributed to the increase of clay content with depth. The samples contain more clay particles in study area which favour more field moisture percentage. These field moisture percentages in study area were favourable for agricultural production but the natural disasters changed their energy level over time.
4.1.2: Hygroscopic Moisture
Analytical results of hygroscopic moisture of the samples are represented in figure (Figure-4.2). The highest hygroscopic moisture was 4.55% in the study site. This sample was collected from Dhalbaria-10 which was located at 22022’31”N and 89001’35”E. The lowest hygroscopic moisture was 0.38%. This sample was collected from Dhalbaria-5 which was located at 22022’42”N and 89001’27”E.
The average value of hygroscopic moisture percentage was 2.23%. Soil water considered to be unavailable to plants includes the hygroscopic water as well. It is portion of capillary water which retained at potential below -1500 kpa (Brady, 2004). These moisture percentages are not favourable for agricultural production.
4.2: Soil Chemical Parameters
4.2.1: Soil pH
Soil pH is the negative logarithm of hydrogen ion concentration in soil solution. To measure the degree of soil acidity and alkalinity, soil pH is a very important variable and it helps to know soil properties chemical, biological and indirectly physical environment including both nutrients and toxins. The activity of micro-organisms, plant growth, biochemical breakdown, solubility and absorption of colloids etc. are known through soil pH (Brady, 2004). The pH of a solution is a measure of the molar concentration of hydrogen ions in the solution and as such is a measure of the acidity or basicity of the solution. The ideal range of pH in soil is 6.0 to 6.5 because most of the plant nutrients are available in this stage (Vossen, 2012). In most cases, a pH range of 6.0-7.5 is optimum for the adequate availability of nutrients in the soils of Bangladesh (BARC, 2005).
The highest pH value was 8.0 and the lowest pH value was 5.85. The average value is 7.06. In the present study area, most of the soil was alkaline (pH > 7.5). This pH is not suitable for agricultural production (SRDI, 2003). The pH below 8.5 indicates saline soil, which is also reported by Brady and Weil (Brady, 2004). In the year 1972, the highest pH value in the study area was 6.85 and the lowest pH value was 5.3 (SRDI, 1972). In the year 1996, the highest pH value in the study area was 7.90 and the lowest pH value was 5.2 (Table-4.2) (SRDI, 2001). The comparison of pH value between 1996 and 2014 is given in Figure-4.3.
The average pH value of soil samples in the study area was 7.06 in 2014 and 6.6 in 1996. The average pH value is increased over time. The pH value has increased day by day due to natural disasters. These natural disasters cause flood which is the reason of saline water intrusion. Another important cause for increasing pH is shrimp culture which affects pedological and environmental change in soil.
4.2.2: Electrical Conductivity
Electrical conductivity (EC) is the important parameter for soil salinity. The result of the EC of the investigated sites in 2014 has been shown in table-4.3. The highest EC value was 15.6 dS/m and the lowest EC value was 1.5 dS/m. The average value is 4.76 dS/m.
In the year 1996, the highest EC value in the study area was 10.0 dS/m and the lowest EC value was 0.5 dS/m (Table-4.3) (SRDI, 2001
4.2.3: Soil Organic Carbon and Organic Matter
Soil organic carbon is important parameter for agriculture. It affects productivity of soil for agricultural production. In the year 2014, the highest value of organic carbon of the study site soil samples was 1.02%. The lowest value of soil organic carbon was 0.43% (Figure-4.6). In the year 1972, the highest soil organic carbon value in the study area was 0.75% and the lowest soil organic carbon was 0.2% (SRDI, 1972). The average soil organic carbon in the study area was 0.71% in 2014 and 0.44% in 1972.
Soil organic carbon (OC) has long been identified as factors that are important to soil fertility in both managed and natural ecosystems (Kucharik et al, 2001). Due to natural disasters, soils were affected by salinity. People were also lost their livelihood who was engaged with agriculture. Traditional agricultural practices such as land clearing and cultivation have led to reduced OC levels in soil worldwide (Russell and Williams, 1982; Dalal and Mayer, 1986). After disasters, people were not interested with traditional agricultural practices. But they were engaged with gher. Gher or shrimp culture was caused to increase organic carbon. The applied feed of shrimp is partially dissolved in water and the rest residue accumulates at bottom of gher. The uneaten feeds and residues are mixed with soil and water and increase organic carbon, because different organic products such as; mustard cakes, cow dung and other phytoplankton are used as shrimp food. The high amount of organic carbon is an indication of their high productivity which also indicates a good soil quality. But due to the different disasters, other environmental condition and essential elements are not available for good agricultural production.
In the year 2014, the highest value of organic matter of the study site soil samples was 1.76 and collected from Ratanpur-5. The lowest value of soil organic matter was 0.75 in the study area (Table-4.4). In the year 1972, the highest soil organic matter in the study area was 1.29 and the lowest soil organic matter was 0.35 (SRDI, 1972). In the year 1996, the highest soil organic matter was 3.70 and the lowest soil organic matter was 1.12 (Table-4.4).
Comparison of Soil organic matter between 1996 and 2014 is given in Figura-4.7. The average soil organic matter in the study area was 1.23 in 2014, 2.35 in 1996 and 0.76 in 1972.
During the period of 1972 to 1996, no remarkable worse disasters hit the experimental area. That’s why organic matter in the study site increased day by day due to cultivation of shrimp culture for economic development. After 1996, most of the worst disasters like Aila and Sidr occurred in Bangladesh. For this reason, people were not engaged with gher and agriculture. For this reason, organic matter was decreased in 2014 in the study area.
4.2.4: Total Nitrogen and C/N Ratio
Soil total nitrogen affects productivity of soil for agricultural production. In the year 2014, the highest value of total notrogen of the study site soil samples was 0.173% and this sample was collected from Ratanpur-5. The lowest value of total nitrogen of soil was 0.026% (Table-4.5).
These results were very close to the findings of Portach and Islam (1984). According to Portach and Islam (1984), hundred percent soils of Bangladesh contained N below critical level. Total N content in study site soils were very much lower than the critical level (0.271-0.36) of total N (BARC, 1997). Bhuiyan (1988) reported that the total N percentage of different soil series of Bangladesh ranged from (0.05 to 0.22%). These findings are similar with those of Chowdhury (1990); Hossain et al. (2003) found that most of the soils were deficient in N content. Total N contents of these soils might be related less addition of organic matter changes in cropping systems, the quality and quantity of these elements in flooding water and variations in soil properties.
In the year 1972, the highest value of soil total nitrogen in the study area was 0.06% and the lowest value of soil total nitrogen was 0.03% (SRDI, 1972).The average value of soil total nitrogen in the study area was 0.102% in 2014, 0.043% in 1972.
Carbon to nitrogen ratios are an indicator for nitrogen limitation of plants and others. Optimum C/N ratio for agricultural purpose is 20-30:1 (Bruland et al, 1988). In the year 2014, the highest C/N ratio in study area was 35:1 and lowest C/N ratio was 4:1. The C/N ratios result of the soils is given below- (Table-4.5). The average value of C/N ratio was 14:1 in 2014 which was less than optimum range. This imbalance occurred due to natural disasters. For this reason, this soil is not good for agriculture.
4.2.5: Cation Exchange Capacity
Cation exchange capacity (CEC) is the important parameter for soil fertility. The effective CEC is increased as pH rises and decreased as pH falls. A drop in pH means a loss of effective CEC and that some cationic nutrients will lose their retention sites. These cations will leach away if no other mechanism of retention is available, such as plant uptake or precipitation in an insoluble form (Hoskins, 1997). Morras (1995) and Turpault et al. (1996) suggested that, clay coatings on coarser particles and partial transformation of silt and sand were the reason for CEC. Soils with high amounts of clay and/or organic matter will typically have higher CEC (McCauleyet al, 2009). In the year 2014, the result of the CEC of the investigated sites in 2014 has been shown in Table-4.6. The highest CEC value was 54.74 meq/100g soils and the lowest CEC value was 18.73 meq/100g soils. The average value is 32.9 meq/100g soils. In the year 1972, the highest value of CEC in the study area was 16.4 meq/100g soils and the lowest value was 10.02 meq/100g soils (SRDI, 1972). Average value of CEC in 1972 was 14.12 meq/100g soils. In the year 1996, the highest CEC value in the study area was 0.1 meq/100g soils and the lowest CEC value was negligible (Table-4.6). In the study area, The CEC values of the soil samples in 2014 is increased than that of in 1996 because of raising up pH values, soil organic matter and high in clay mineral.
High CEC means higher nutrients can be held by the soil and fewer remain in soil solution. Natural disasters and shrimp culture increases the pH and organic matter of the study site which ultimately increases the CEC level of the study area.
4.2.6: Exchangeable K
Of all essential elements, potassium is the third most likely, after nitrogen and phosphorus, to limit plant productivity (Brady, 2004).
In the year 2014, the highest value of exchangeable K of the studied soil samples was 21.6 meq/100g soils which collected from Dhalbaria-3. The lowest value of exchangeable K of soil was 5.5 meq/100g soils (Table-4.7).
The ideal range of K saturation varies by crop, but is typically 3-5% of CEC (Hoskins, 1997). The average CEC value was 32.9 meq/100g soils and 3-5% of the CEC is 0.99-1.65 meq/100g soils. But most of the result of exchangeable K in 2014 is more than this value.
In the year 1972, the highest value in the study area was 0.43 meq/100g soils and the lowest value was 0.10 meq/100g soils (SRDI, 1972). In the year 1996, the highest value of soil exchangeable K in the study area was 0.80 meq/100g soils and the lowest value was 0.21 meq/100g soils (Table-4.7). The comparison of exchangeable K between 1996 and 2014 is given in Figure-4.8
The average value of exchangeable K in the studied samples was 10.36 meq/100g soils in 2014, 0.55 meq/100g soils in 1996 and 0.23 meq/100g soils in 1972. The average value of exchangeable K is increased over time. Due to natural disasters and shrimp cultivation or intrusion of saline water, pH and soil CEC are increased. These affect exchangeable K in soil.
4.2.7: Exchangeable Na
Sodium is not a plant nutrient and therefore is not necessary for plant growth. High levels of sodium are detrimental to soil tilth and plant growth (Marx et al, 1999).
In the year 2014, the highest value of exchangeable Na of the studied soil samples was 480 meq/100g soils. The lowest value was 280 meq/100g soils (Figure-4.9).
In the year 1972, the highest value of exchangeable Na of the studied samples was 0.55 meq/100g soils and the lowest value was 0.34 meq/100g soils (SRDI, 1972).
The average value of exchangeable Na in the study area was 363.5 meq/100g soils in 2014 and 0.43 meq/100g soils in 1972.
The average value of exchangeable Na is much increased over time. This might be due to the increase of soil pH and soil salinity by worst natural disasters and shrimp cultivation or intrusion of saline water after natural disasters.
This level of exchangeable Na is very excessive for soil (Marx et al, 1999 and Hoskins, 1997).
This range is very critical for agricultural production and retards crop growth.
4.2.8: Exchangeable Ca
If the pH is very low or low, calcium is rated medium. Calcium is rated high if the pH is medium or higher (Buchholz, 1983). If Ca is present <5 meq/100g soils, the class of this soil is low for Ca. If it is present 5-10 meq/100g soils, the soil class is medium and if the range is >10 meq/100g soils, the soil class is high for Ca in a soil (Marx et al, 1999). The ideal range of Ca saturation is 60-80% of the soil CEC. When Ca exceeds 80% of the soil CEC, it is rated excessive (Hoskins, 1997).
In the year 2014, the highest value of exchangeable Ca was 282.7 meq/100g soils and this sample was collected from Ratanpur-4. The lowest value was 110.4 meq/100g soils (Table-4.8).
The pH of most of the soil samples in the study area is >7.5 which indicates more Ca is exchangeable in this pH range (Buchholz, 1983). For this reason, these soils have shown more exchangeable Ca. The average value of exchangeable Ca 186.5 meq/100g soils which is 566.95% of the CEC (average CEC is 32.9 meq/100g soils). This value is very excessive for Ca in the study area. This result is similar with the result of Hoskins, 2001 and Marx et al, 1999.
In the year 1972, the highest value of exchangeable Ca in the study area was 8.83 meq/100g soils and the lowest value was 3.23 meq/100g soils (SRDI, 1972). In the year 1996, the highest value of soil exchangeable Ca of the studied soil samples was 14.6 meq/100g soils and the lowest value was 8.8 meq/100g (Table-4.8).
The average value of exchangeable Ca was 11.68 meq/100gsoils in 1996 and 6.63 meq/100gsoils in 1972. The average value of exchangeable Ca is much increased over time. Due to natural disasters and shrimp cultivation or intrusion of saline water, exchangeable Ca is increased over time. This range is very critical for agricultural production. The comparison of exchangeable Ca between 1996 and 2014 is given in Figure-4.10.
4.2.9: Exchangeable Mg
If Mg is present <0.5 meq/100g soils, the class of this soil is low for Mg. If it is present 0.5-1.5 meq/100g soils, the class is medium and if the range is >1.5 meq/100g soils, the class is high for Mg in a soil (Marx et al, 1999).
The ideal range of Mg saturation is 10-25% of the soil CEC. When Mg exceeds 25% of the soil CEC, it is rated excessive (Hoskins, 1997).
In the year 2014, the highest value of exchangeable Mg was 61.2 meq/100g soils. The lowest value was 31.9 meq/100g soils (Table-4.9). In the year 1972, the highest value of exchangeable Mg of the studied soil samples was 2.60 meq/100g soils and the lowest value was 1.57 meq/100g soils (SRDI, 1972). In the year 1996, the highest value of soil exchangeable Mg was 9.97 meq/100g soils and the lowest value was 4.63 meq/100g (Table-4.9).
The average value of exchangeable Mg in the study area was 42.03 meq/100gsoils in 2014, 6.93 meq/100g soils in 1996 and 2.15 meq/100g soils in 1972. Figure-4.11 has been shown the comparison of Exchangeable Mg between 1996 and 2014.
The average value of exchangeable Mg is much increased over time which might be due to the increase of soil pH and soil salinity by worst natural disasters and shrimp cultivation or intrusion of saline water after natural disasters.
This level of exchangeable Mg is very excessive for soil (Marx et al, 1999; Hoskins, 1997). This range is very critical for agricultural production and retards crop growth.
4.2.10 Exchangeable Na Percentage
Exchangeable Na percentage or ESP is a good indicator of soil for agricultural production. The soils that have high ESP (greater than 15) are classified as saline-sodic soils and the soils have ESP less than 15 are classified as saline soils (Brady, 2004).
In the study area, the highest value of ESP was 14.9% and lowest value was 7.3% in 2014. Figure-4.12 has been shown the ESP value of the study area. This value indicates that, the soils of the study area might be saline soils.
4.3: Impact on Agriculture
Natural disasters affect agricultural production. Agricultural production in 1996 was not very worst but it was delinquent in 2012-13. It has been shown below (Table-4.9). Figure-4.13 has been shown the comparison of crops production between 1995-1996 and 2012-2013.
This result shown that, agricultural production has reduced from 1996 to 2012-13 for rising up salinity level of the soil in the study area. Between 1996 to 2012-13, two most devastating cyclone occurred in Bangladesh. These cyclones were upset for agricultural production. On the other hand, salinity intrusion, shrimp culture, crabs culture etc increase the salinity level of soil in the study area. These activities are mischievous for this type of worst agricultural production.
SUMMARY AND CONCLUSION
The coastal areas of Bangladesh cover more than 30% of cultivable lands of the country but these areas are affected by various types natural disasters like cyclonic storms, salinity intrusions, tidal surges, flood and drought etc. most climate releted hazards in Bangladesh are linked to soils by affecting their properties to various extent. So, present study has been undertaken with an aim to investigate the soil properties and the crop production of a south western disaster-prone area of Bangladesh as affected by different types of natural hazards. Therefore two unions of Kaliganj Upazilla, Ratanpur and Dhalbaria under Sathkhira district have been selected for the purpose. Twenty defferent soil samples and Information were collected from the study area following quantitative and qualitative methods. The samples were studied and the results revealed that
- Range of field moisture of the soil samples is 19.07-11.92%.
- Range of hygroscopic moisture of soil samples is 4.55-0.38%.
- Soil textural classes of study area vary between silt loams to silty clay loams.
- Soil pH is between 8 and 5.5 and average value of pH is 7.06.
- Soil organic matter ranges between 1.76% and 0.75%.
- Total nitrogen ranges from 0.17% to 0.02%.
- The range of C/N ratio is 35:1-4:1. Average ratio is 14:1.
- Cation exchange capacity varies between 54.7-18.7 meq/100g soils.
- Exchangeable Na percentage or ESP varies between 14.9-7.3%.
Bangladesh is covered with different types of natural disasters and thought to be one of the most vulnerable countries of the world. Cyclone is an ultimate induced disaster occurs in Bangladesh almost every year. Most marginalized communities living in remote villages along Bangladesh’s coastal zone which are exposed to cyclonic hazards. The disastrous cyclone adversely affects the whole environment including human beings, their shelters and the resources essential for their livelihood such as soil, water etc. Soil is a collection of natural bodies that supports plant growth is adversely affected by cyclonic hazards. Soil salinity is the consequent effect of this disaster. During the research work soil physical and chemical parameter and agricultural status were studied. It was seen that physical parameters were in favourable condition but chemical parameters were in critical range that impede agriculture.
There have no control over natural disaster. It should be tried to cope up with the present situation by taking appropriate measures. Introduction of land use zoning, shrimp culture would do less adverse effect to crop agriculture. Furthermore, cultivation of salt tolerant crop varieties will be effective for the study area.
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Abdulla Al Mamon
Department of Soil, Water and Environment (Session: 2008-2009)
University of Dhaka