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Physico-chemical Characteristics of the Seasonally Flooded Soils of Bangladesh and Their Management Implications

K. F. AKTER
Department of Soil, Water and Environment, University of Dhaka, Dhaka‐1000, Bangladesh

Z. H. KHAN
Department of Soil, Water and Environment, University of Dhaka, Dhaka‐1000, Bangladesh

M. S. HUSSAIN
Department of Soil, Water and Environment, University of Dhaka, Dhaka‐1000, Bangladesh

A. R. MAZUMDER
Department of Soil, Water and Environment, University of Dhaka, Dhaka‐1000, Bangladesh

Abstract/ Executive Summary:

The seasonally flooded soils of Bangladesh are unique in respect of several specific characteristics and contribute toward producing bulk of its staple food - mainly rice. Having fine texture these soils are similar to the “paddy soils” of Southeast Asian floodplains and have high production potential under proper management. Six representative soil series, viz. Arial, Debidwar, Naraibag, Jalkundi, Siddirganj and Tippera from the central region of Bangladesh have been studied to evaluate some of their intrinsic physico-chemical properties and their sustainable management requirements. These soils are slightly acidic to neutral and are negatively charged with ΔpH values ranging between –0.2 and –1.2. The organic matter content in the surface soil is relatively low that decreases steadily with depth. The cation exchange capacity (CEC) of the soils varies on the basis of their clay and organic matter contents while base saturation per cent (BSP) is high. The contents of available N, P, K and S and DTPA-extractable Fe, Mn, Cu and Zn in soils are moderate and are commensurate with the contents of colloidal fractions. These soils receive several mineral nutrients annually with the sediments deposited during the monsoon floods. The characteristics like organic matter content, particle size distribution, CEC, pH and BSP that have important management implications have been discussed.

Keywords: Seasonally flooded soils, Physical and chemical attributes, Management implications

Location: Central hydroecological region of Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Land management

Objectives:

1. To highlight the phygico?chemical characteristics of several representative seasonally flooded soils developed in the central region of Bangladesh for determining their abilities to maintain sustainable productivity for its fast growing population.

Methodology:

The study area covers over a million hectare in the central hydro?ecological region of Bangladesh. Soil samples for the study have been collected from river alluvia of the GBM system. The exact locations of the selected pedons were determined with GPS and were shown in the above figure. A total of 30 soil samples were collected from six pits on natural horizon basis. The soil samples were duly processed, preserved and analyzed for determination of their physico?chemical characteristics. The morphological and chemical properties of the studied soils have also been discussed. The annual flooding characteristics, subsoil horizon, plough?pan, flood coatings, matrix colour and mottles and consistence are the notable morphological features relevant to the management of these soils. The particle size analysis of soils has been carried out by sieving and using hydrometer method as per Gee and Bauder. The pH determination has been done using glass electrode in soil suspensions in H₂O and 1 M KCl. The ΔpH was calculated by subtracting pH in H₂O values from pH in KCl values. Organic carbon was determined by Walkley and Black wet oxidation method and total nitrogen was estimated by digestion of the soil in the sulfuric acid followed by a Kjeldahl distillation. CEC was measured leaching the soil sample with neutral 1 N ammonium acetate solution and exchangeable bases were determined from the same 1 N ammonium acetate leachate using atomic absorption spectrophotometer. Available N, P, K and S have been determined using standard volumetric and colorimetric procedures. Determination of available Fe, Mn, Cu and Zn was done from DTPA?CaCl₂ extracts using atomic absorption spectrophotometer.

Source of Information: Dhaka Univ. J. Biol. Sci. 20(2): 173‐182, 2011 (July)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

It must be noted that because of multiple cropping the problem of nutrient shortage and loss have developed in these seasonally flooded soils. Researches have shown that the quantities of nutrient elements from the soil system per hectare to produce the stated quantity of rice is 45 Kg N, 25 Kg P₂O₅ and 70 Kg K₂O while the quantites of nutrient elements added to the soil system per each transplanted HYV paddy (boro and aman) are 100 Kg N, 35 Kg P₂O₅ and 45 Kg K₂O. The quantity of nitrogenous fertilizer added in excess to the soil system is lost due to volaltilization, leaching, run?off and/or consumed due to growth of weeds while the excess quantities of phosphates and potash either get fixed in the soil system or remain as residues. Proper and scientific management of soil health and their sustained productivity can be maintained through balancing the incoming nutrients due to fertilizer addition, biological fixation, weathering of biotite and feldspar minerals, precipitation of thunder storms and decomposition of organic residues and the outgoing with the volatilization, etcetra. The soil properties though have roles in the management of soil but that only contribute if and when all the above factors are duly taken into consideration.

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