Effect of Net Surface Charge and NH4+ Exchange Selectivity on Ammonium Fixation of Soil Clays

10.30058/SE.200106.0002

H. J. Chen；Y. M. Tzou；T. C. Juang；M. K. Wang

Quantity-intesity (Q/I) ； Point of zero negative charge (PZNC) ； Potential buffering capacity (PBC) ； Gapon selectivity coefficient (KG) ； Activity ratio of NH4+ and Ca2+ (AR0) ； labileammonium (-ΔNH4)

土壤與環境

4卷2期（2001 / 06 / 01）

93 - 103

英文

The quantity-intensity (Q/I) relationship of potassium has been long proposed by soil secientists. Net surface charge and ammonium exchange selectivity were also shown to correlate with ammonium fixation of soil clays. This study aimed to investigate the effect of the net point of zero charge (PZNC), potential buffering capacity (PBC), Gapon exchange selectivity coefficient (KG);labile –ΔNH4 and the activity ratio of NH4+ to Ca2+ (AR0) on ammonium fixation with or without the presence of K+. Twelve surface (0~30 cm) soil clays in Taiwan were collected for this study. In the absence of K+, the correlation coefficient (R) of PZNC versus the Gapon selectivity coefficient (KG1) is 0.7335. At high PZNC, the sesquioxide contents showed more effect on KG1 than 2:1 layer silicates. In the presence of potassium, no relationship exists between PZNC, KG2 and PBC2. Increasing the net surface negative charge of clays decrease the KG1 and KG2 values, and their ammonium exchange coefficient. There are nine soil clays with PBC1values greater than 500 cmolc kg-1 (mol L-1)1/2 for ammonium fixation, while only three soil clays have PBC1 values less than 500 cmolc kg-1 (mol L-1)1/2. In the absence K+, the KG1 values are in the range of 6.1nad 8.4 (L mol-1)1/2. However, in the presence of K+, the KG2 values are in the range between 8.0 and 29.1 (L mol-1)1/2. The R value of KG1 versus PBC1 and CEC are 0.8540 and 0.7334, respectively. The values of the labile –ΔNH41 increase with increasing PBC1 (R= 0.7660). On the other hand, in the presence of K+, the R value of ammonium fixation versus PBC2 is higher than that of ammonium fixation versus PBC1. The R value of PBC2 versus KG2 is 0.8030. The twelve soil clays in this study have AR01 (mol L-1)1/2 values in the range between 0.001 and 0.01 (mol L-1)1/2. The AR01 values correlate with illite contents. Reducing ilite contents in soil clays decreases the weathering of the wedge zone to fix ammonium and increases the ammonium fixation on the planar positions.