Pedosphere 11(4): 369--375, 2001
ISSN 1002-0160/CN 32-1315/P
©2001 Soil Science Society of China
Published by Elsevier B.V. and Science Press
| Effect of potassium on ammonium fixation and adsorption of vermiculite in binary and ternary systems |
| FENG Ke, WANG Xiao-Zhi, TANG Yan and WANG Xiao-Li |
| Agricultural College, Yangzhou University, Yangzhou 225009 (China) |
| ABSTRACT |
| Ammonium fixation and adsorption experiments were conducted to study the effect of potassium on ammonium fixation into interlayer of vermiculite and ammonium adsorption at the surface of vermiculite both in the binary (NH4+-Ca2+) and ternary (NH4+-K+-Ca2+) systems. In the ammonium fixation experiment, 5 mmol NH4+ kg-1 was added alone, or after, before or simultaneously with 5 mmol K+ kg-1 to the vermiculite (vermiculiteaolution=1:1), and the incubation was conducted for 3 days under constant 20 0C. In the adsorption experiment, after addition of 10 mmol Ca2+ L-1 as matrix ions, either NH4+ alone with a concentration series from 0.1 to 5.0 mmol NH4+ L-1(binary exchange system of NH4+ and Ca2+) or NH4+ together with 5 mmol K+ L-1 (ternary exchange system of NH4+, K+ and Ca2+) was added to vermiculite at a vermiculite to solution ratio of 1:10 for 24h equilibrium. The results of the fixation experiment showed that the presence of K+ increased NH4+ fixation for all the treatments, regardless of the addition orders. For ammonium adsorption a linear relationship between activity ratios of NH4+ to Ca2+ and Mg2+ in the equilibrium solutions (ARNH4) and increases of exchangeable NH4+ at the surface of vermiculite after 24h equilibrium (ΔEx-NH4+) was shown for almost the whole concentration ranges tested. Compared with the binary system, the elope of the curve of the ternary system was steeper, indicating a more intensive adsorption of NH4+ in the presence of K+. It was demonstrated that K+ did not reduce the ammonium fixation into the interlayer and ammonium adsorption at the surface of vermiculite, which indicated that, under the experimental conditions of this study, K+ did neither occupy the sites for NH4+-fixation in the interlayer nor the sites for NH1-adsorption at the surface of vermiculite. |
| Key Words: adsorption, ammonium, fixation, potassium |
| Citation: Feng, K., Wang, X. Z., Tang, Y. and Wang, X. L. 2001. Effect of potassium on ammonium fixation and adsorption of vermiculite in binary and ternary systems. Pedosphere. 11(4): 369-375. |
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