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Changes in Fertility Status of Soils in Six Soil Series of Chakaria Sundarbans Mangrove Forest in Bangladesh

Md Razib Rahman
Soil Resource Development Institute, Farmgate, Dhaka, Bangl adrsh

Md Babul Hossain
Soil Resource Development Institute, Farmgate, Dhaka, Bangl adrsh

Abstract/ Executive Summary:

A comparative study was made during January to July 2012 to assess the impact of deforestat ion on changing fertility status on six soil series of Chakaria Sundarbans mangrove forest over time. Primary data have been generated through semi-detailed soil survey, GIS techniques, time series land use maps, starting from the base year of 1974 to 2012 and soil chemical analysis. Review of secondary data on land and soil has been done and tertiary data have been generated. Soil physical and chemical analyses have been made following convent ional soil analysis methods and as followed during Reconnaissance Soil Survey (RSS) carried out in 1973. Six identified soil series viz. Badarkhali, Barabakia, Chakaria, Cheringa, Kutubdia & Pahartali have been considered for the study. Some physical parameters and nutrient elements were analyzed in the study area for assessing long term changes (1973 to 2012) in physical, chemical and physico-chemical properties of soil. Analysis of nutrients has been made for determining soil fertility changes during 1990 to 2012. Organic matter decreased from medium to low, nitrogen from low to very low, phosphorus from optimum to very low. Potassium and zinc remains in very high fertility class but their level decreased substantially. Sulphur and boron also remained very high fertility class but their level increased in many folds. In general, depletion of soil fertility is mainly due to intensive exploitation of land for salt production, shrimp culture and agriculture without proper replenishment .

Keywords: Fertility Status of Soils, Six Soil Series of Chakaria Sundarbans

Location: Chakaria Sundarbans, a deforested area of Cox's Bazar district of Bangladesh

Start Date: 00-00-1974

End Date: 00-00-2012

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

1. To study the changes in fertility status of the soils due to deforestation in different soil series over time.

Methodology:

Selection of the study area The study has been conducted in Chakaria Sundarbans, a deforested area of Cox `s Bazar district of Bangladesh. It lies in the delta of Matamuhuri River of Cox’s Bazar district. Six identified soil series viz. Badarkhali, Barabakia, Chakaria, Cheringa, Kutubdia & Pahartali have been considered for the study. The basis of the soil survey was air photo interpretation supported by a planned program of field traverses, which has done in 1973 during reconnaissance soil survey of SRDI. The other basis was laboratory analysis of representative soil samples of selected series that were collected from the same sites indicated in RSS report, 1973. Current use patterns of the area were taken from topographic map and administrative map and updated with the interpretation of Land sat TM images. Geometric correction was performed with bilinear transformation and the root mean square error was (0.49) controlled within less than one pixel for 42 ground control points (GCPs). Ground data were obtained by field investigation. The morphological properties of the soils were studied in the field following the methods of USDA as described in Soil Survey Manual. Soil series identification The nomenclature of FAO, as described in the booklet “Guideline for Soil Description” which is essentially derived from the USDA Handbook 18, the Soil Survey Manual has been followed. Color notation has described according to the Munsell Soil Color Chart (Munsell Color Company). The main soil unit recognized was the soil series during RSS done by SRDI. Wherever soils with similar properties occur in the survey area and elsewhere, they are called by the same name. Soil samples for analysis Organic carbon: The organic carbon content of the soils was determined volumetrically by Walkley and Black’s wet oxidation method. Organic matter: Soil organic matter was calculated by multiplying the percent value of organic carbon with conventional van-Bemmelen’s factor of 1.724. Total nitrogen: Total nitrogen was determined by micro-kjeldhal’s method after digestion with H₂SO₄. Available P: Soil P was extracted and determined by ascorbic acid blue colour method. Available S: Available soil S was extracted by calcium phosphate and determined turbidimetrically. Available K: Available Soil K was extracted by 1M NH₄OAc and determined flame photometrically. Available B: Available soil B was extracted by 0.01M calcium chloride. Available Fe, Mn, Zn and Cu: Available soil Fe, Mn, Zn and Cu was extracted by DTPA ex tracting solution and determined by AAS.

Source of Information: BANGLADESH RESEARCH PUBLICATIONS JOURNAL; ISSN: 1998-2003, Volume: 10, Issue: 4, Page: 369-375, January - February, 2015

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The available N and P content in the soils seem to be deficient for plant growth. As the soils are highly acidic, the available P is obviously low as most of the P becomes fixed. Low application of phosphorus fertilizers may another reason for the decreasing available P in the crop cultivating area. Very high amount of available sulphur in the soils are possibly due to oxidation of pyrites and jarosites during flashing and flooding of the soils with rain water in the monsoon months. The high S contents may be attributed to the presence of sulphuric horizon within the profiles which is harmful to crops. This study demonstrated soil fertility status in relation to some selected physical and chemical characters. The physical and chemical attributes of soils could be protected from depletion of fertility by a number of general types of management practices.

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