MINERALOGY OF SOILS FROM DIFFERENT AGR0ECOLOGICAL REGIONS OF BANGLADESH: REGION 5—LOWER ATRAI BASIN AND REGION 6—LOWER PURNABHABA FLOODPLAIN

摘要

Bangladesh has been divided into 30 Agroecological Regions (AEZs) and the applied agricultural research has currently been conducted on this basis. In context of the lack of enough mineralogical information on the AEZ basis, an attempt has been taken to study mineralogy of important soils from all AEZs of Bangladesh in order to provide basic information for applied research. As a part of this attempt, the mineralogy of ten soils from the Lower Atrai Basin (AEZ 5) and six soils from the Lower Purnabhaba Floodplain (AEZ 6) has been reported in this paper. The soils of both AEZs were acidic in nature, had moderate to high amounts of clay, and the texture was medium (silt loam) to heavy (clay). The 2-20 μm silt fraction of the soils having more than 25% of clay (Laskara-1, Laskara-2, Tarash-1 and Tarash-2 soils of AEZ 5 and all soils of AEZ 6) was composed mainly of quartz, with small amounts of mica, plagioclase, K-feldspar and chlorite, while other six soils of AEZ 5 (having less than 25% of clay) had relatively lower amounts of quartz (but still dominant) with fairly good amounts of mica, chlorite and plagioclase and low amounts of K-feldspar. Similarly, the <2 μm clay fraction was dominated by mica along with interstratified kaolinite-smectite and mica-vermiculite-smectite minerals in the former group of soils having the higher clay content while with vermiculite in the latter group of soils having the lower clay content. The impact of mineralogy on the genesis and classification of soils in AEZs 5 and 6 has been discussed.