Morphology and Characterization of an Acid Sulfate Soil from Mangrove Floodplain Area of Bangladesh.

Abstract

The studied soil was in ripe condition(field n — value‹0.6)and consisted of more than 3 horizons including sulfuric horizon within the 1.2 m of the soil surface.The soil pH was low(‹4 : field)and ECe values(0.72—1.62 S m-1),soluble cations and anions,and exchangeable bases were relatively high throughout the profile.Water soluble SO/- —S content was more than 1 g kg-1 and the total S content at ground water saturated portion (C horizon) of the soil was about 12 g kg-1. The exchangeable hydrogen content(l. 1—4.4 cmol( + )kg-,)was very high,and it was attributed to the oxidation of pyritic sulfur.The high amounts of exchangeable and active Fe and Al contents of the soil can be used to categorize it as an actual acid sulfate soil. The soil had high amounts of kaolinite and illite minerals in the clay fraction(‹0.002 mm)throughout the profile. The soil had trace amounts of smectite,chlorite, vermiculite, quartz, feldspars and interstratified 0.71 nm/1.01 nm and 1.01 nm/1.42 nm minerals.The x—ray diffraction patterns showed that jarosite was present at the deeper parts of the profile, which was attributed to the oxidation of pyrite to jarosite.The amount of 0.71 nm mineral was high in the A horizon compared to in C horizon which might be due to pedogenesis.The soil is categorized into Inceptisol order,Aquepts suborder and Sulfic Haplaquepts great group.