Mineralogical Characteristics and Potassium Quantity/ Intensity Relation in Three Indus River Basin Soils

摘要

Mineral characteristics in the Indus basin are less understood making it difficult to extrapolate the field experimental results.The clay layer charge and other mineral characteristics were determined and related to potassium(K)quantity/intensity(Q/I)relation as an index for potassium bioavailability.Three soils,namely:(1)Gujranwala,fine-loamy,mixed,hyperthermic Typic Haplustalf;(2)Peshawar,fine-silty,mixed,hyperthermic Haplocalcidic Haplustept and(3)Lyallpur,fine-silty,mixed,hyperthermic Ustic Haplocambid,which vary in profile development,were sampled at diagnostic horizons and fractionated into sand(+50 mu m),silt(50-2 mu m),coarse clay(2-0.2 mu m)and fine clay(< 0.2 urn)size separates.Mineralogy of each size-separate was examined by X-ray diffraction;layer charge of the fine clays phyllosilicates by the alkylammonium exchange method(nC=5 to 18);and di-vs.trioctahedral structural nature by an assay of Fe~(2+)+Mg~(2+).For the same samples,K Q/I parameters were determined from K adsorption isotherm fitted to Langmuir equation.The sand and silt fractions contained mica(both di-and trioctahedral),quartz,feldspars and chlorite.The shale derived Peshawar soil had smaller and lesser mica and more chlorite than the alluvial Gujranwala and Lyallpur soils.The coarse clay had mainly mica,kaolinite and smectite and in addition,chlorite and quartz in case of semi-arid Peshawar and Layllpur soils.The fine clay was composed of mainly smectite,mica and kaolinite.Most clay particles had layered structure with discrete boundaries as seen under transmission electron micrograph.The clays from Peshawar and Layllpur soils had 2 to 3 times greater Fe~(2+)+Mg~(2+),low layer charge density smectite(fine clay)compared to the Gujranwala which also had partially opened mica(wedges)seen with HRTEM.The Layllpur and Peshawar soils although had less potassium buffering capacity but had 2 to 4 times greater K~+activity in 0.002 M CaCl2 solution than the Gujranwala and showed potassium release as opposed to adsorption in the later soil.The study will help to explain the results of field experiments and extrapolation to other soils.