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Morphogenesis of Three Surface Water Gley Soils from the Meghna Floodplain of 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

F. OTTNER
Institute of Applied Geology, University of Natural Resources and Applied Life Sciences, Peter-Jordan Str.70, 1190 Vienna, Austria.

Abstract/ Executive Summary:

Surface?water gley soils comprise extensive area on the seasonally wet landscape of Meghna floodplain in Bangladesh. Three typical surface?water gley soils from the above floodplain were studied in the field and laboratory for their pedogenesis. Morphological properties indicate that there is formation of gleyed/ pseudogleyed horizons in the soil profiles. Extensive development of mottles, ploughpans and flood coatings or gleyans is the most notable morphogenetic features in these soils. Physically, these soils are medium to fine textured where textural class ranged between silt loam and silty clay. Chemically, the soils are moderately acidic to neutral in reaction with seasonally fluctuating pH in the surface horizon. The ΔpH values are all negative and range from – 0.90 to – 2.01. The organic matter content in the surface soil is relatively low that decreases steadily with depth. The cation exchange capacity (CEC) of the soils ranged from 3.53 to 14.08 cmol p+/kg with an average of 10.10 cmol p+/kg and base saturation per cent (BSP) varied from 59 to 86. The Ca++/Mg++ ratio is less than unity indicating loss of Ca++ due to gleization in these soils.

Keywords: Meghna floodplain, Morphogenesis, Soil chemico-physical properties

Location: Meghna floodplain soils in Bangladesh

Start Date: 00-00-2011

End Date: 00-00-2011

Program Area: Crop-Soil-Water Management

Commodity: Land degradation

Objectives:

1. The present communication reports a study of the morphology and some chemico-physical characteristics of the soils to ascertain their pedogenesis.

Methodology:

This study was conducted on the Meghna floodplain soils in Bangladesh. The study area represents smooth, nearly level landscape of floodplain ridges and basins consisting of unconsolidated alluvium. The area under study experiences seasonal flooding of various depths and durations during the monsoon months. Ridges remain mainly above normal flood level while parts remain seasonally shallowly flooded for a period ranging from 1 ? 2 months. The basins or basin depressions are flooded more deeply and for a longer period. The climate of the area is humid tropical monsoon with a mean annual temperature of 25.5⁰C and an annual rainfall of around 2250 mm(8). The temperature regime is hyperthermic and most of the agricultural fields have aquic moisture regime. The area under study had been used for large scale paddy and jute cultivations for centuries. Broadcast aus/jute ? transplanted aman followed by Rabi crops and boro ? fallow or transplanted aman is the cropping pattern of this area. The sampling sites were selected to represent major typical surface-water gley soils in the Meghna floodplain. Three profiles from three extensive soil series viz., Tippera, Debidwar and Burichang were selected in three selected sites for soil sample collection. Pits were dug in the selected sites and soil profiles were described in the field according to the procedures outlined in the Soil Survey Manual. A total of 18 soil samples were collected from the three selected profiles on genetic horizon basis. The samples were processed properly and analysed in the laboratory for determining their physical and chemical properties. The pH was determined 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. Particle-size distribution was carried out by sieving and using hydrometer method. Organic carbon was measured 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. Cation exchange capacity (CEC) was measured with 1 N ammonium acetate solution at pH 7.0. and exchangeable bases were determined from the same 1 N ammonium acetate leachate using atomic absorption spectrophotometer. Exchangeable K+ and Na+ were determined with a flame photometer.

Source of Information: Dhaka Univ. J. Biol. Sci. 21(2): 17‐27, 2012 (January)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Alternate wet and dry conditions produce vertical cracks leading to big prisms in the soil profiles. With the passage of time, the horizontal cracks and combined effect of flocculation, root penetration, organic matter addition and the biotic activity produced angular and sub?angular blocky structures in the studied soils. These structural B horizons have been considered as cambic B horizons. Formation of structure in these soils is relatively faster than in other soils. The structure is massive in the surface horizons because of ploughing for many years with puddling. Structurelessness in the lower most horizons was also observed in these soils.

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