Soil mineralogy and potassium quantity/intensity relations in three alluvial soils from Pakistan

Abstract

The pedons investigated are generally weakly differentiated and are slightly weathered. The Gujranwala profile is the most developed among the three. The field and laboratory observations about the occurrence of argillans are contradicting. In view of the available evidences, the following classification is proposed: (1) Gujranwala, Fine-loamy, mixed, hyperthermic Udic Haplustalf (same as original), (2) Peshawar, Fine-silty, mixed, hyperthermic, Udic Ustochrept, and (3) Lyallpur, Fine-silty, mixed, hyperthermic Typic Camborthid. The sand and silt fractions of these soils contain mica, quartz, and feldspars as dominant minerals. Chlorite, kaolinite and calcite are present as relatively less abundant minerals. The sand and silt contain both di- and trioctahedral mica. Mica particles in the Peshawar profile are smaller and less abundant than in the Gujranwala and Lyallpur soils. The coarse clays are composed of mica, kaolinite, chlorite, and quartz. The fine clays are composed of smectite and mica with small amounts of hydroxy-interlayered vermiculite and kaolinite. The surface horizons contain greater mica contents compared to the subsurface horizons which is attributed to sedimentation of mica through irrigation in the Ap horizon. The Lyallpur and Peshawar soils have lower charge density clays than the Gujranwala soil. The Fe(II) + Mg contents were the highest in the Lyallpur clay and the lowest in the Gujranwala clay. The higher Fe(II) + Mg contents suggest trioctahedral nature of smectite and a high amount of unweathered biotite. The influence of clay content, clay mineral suite, layer charge density, and structural Fe(II) + Mg content on the potassium quantity intensity (Q/I) parameters were investigated in these soils. The Q/I parameters: (1) Equilibrium activity ratio of K (AR[^K]e ), (2) Exchangeable K (ExK[0]), (3) Potassium adsorbed on interlayer and wedge site (ΔK[iw] ) , and (4) Potential buffering capacity of potassium (PBC[^K]) were determined. Pair-wise correlation analysis indicated that AR[^K]e was negatively correlated with concentration of both coarse and fine clay size smectite in the soil and positively correlated with structural Fe(II) + Mg contents of the coarse clays. The quantity of exchangeable K (ExK[0]) showed a reverse trend...