Mineralogical Composition of Some Selected Paddy Soils of Bangladesh

Abstract

Soil mineralogy, which largely affects the productivity of soil in low input agriculture, was determined for 28 widely distributed paddy soils from different agroecological regions (AEZs) of Bangladesh. In addition, particle-size distribution was analyzed through fractionation of soil particles into five groups viz. <2, 2-20, 20-53, 53-200 and 200-2000 μm fractions. They represented 3-45, 6-59, 6-41, 3-41 and 0-49% of soil particles, respectively. The 2-20 μm silt fraction appeared to be the dominant fraction for most of our studied soils (17 out of 28 soils). The XRD patterns of the <2um clay fraction indicated the presence of five layer silicate (mica, smectite, chlorite, vermiculite and kaolinite) and four complex minerals (quartz, feldspar, goethite and lepidocrocite) and two interstratified minerals (vermiculite-chlorite and mica-chlorite). Mica (20-50%) was the most predominant mineral identified in all the studied soils. Next to mica, chlorite (5-20%) and kaolinite (2-37%) were present in all the soils. Vermiculite (2-16%) was identified in 20 soils while smectite (1-11%) was identified in only 5 soils. In addition, vermiculite-chlorite intergrade (1-11%) and interstratified mica-chlorite (1-13%) was detected both in 11 soils. Other than layer silicates, quartz (4-21%) was the predominant non-silicate mineral identified in all the studied soils. Next to quartz, feldspars was identified in 26 soils with an approximate relative percentage ranges between 3 and 12%. Very small amount of goethite (1-2%) and lepidocrocite (1-3%) were identified only in 4 and 5 soils, respectively. According to the clay mineralogical composition, most of the studied soils were found at the initial stage of weathering, indicating the high potential to sustain low input subsistence agriculture.