Pedosphere 7(1): 49--58, 1997
ISSN 1002-0160/CN 32-1315/P
©1997 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Thermodynamic properties of NH4+ fixation in manured loess soil in Shaanxi Province, China
FAN Xiao-Lin1, ZHANG Yi-Ping1, JUANG Zo-Chuan2 and ZHANG Fu-Suo3
1 Soil Science Department, Northwestern Agricultural University, Yangling 712100, Shaanxi (China)
2 Research Institute of Soil Science, National Chung-Hsing University, Taiwan (China)
3 Department of Plant Nutrition, Beijing Agricultural University, Beijing 100083 (China)
      Some thermodynamic properties of NH4+ fixation by loess soil in plowing and clay layers are discussed. The results indicate that the four ion adsorption equations commonly used can describe the properties of NH4+ fixation in these soils under constant temperature. Among the four adsorption equations, the single-surface Langmuir equation is the best. When the concentration of NH4Cl solution is 10-1 mol below, the Freundlich equation can be used. The changes of apparent standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) illustrate that NH4+ fixation in soil is an endothermic adsorption and spontaneous reaction, and the process can be enhanced by a higher temperature and clay content in soil. The "proper value of NH4+ fixation by soil (K1 × qm) increased with increasing clay content and temperature. The heat of NH4+ fixation in soil (Qm) confirms the conclusions made in this paper.
Key Words:  NH4+ fixation, free energy, enthalpy, entropy, heat of NH4+ fixation in soil
Citation: Fan, X. L., Zhang, Y. P., Juang, Z. C. and Zhang, F. S. 1997. Thermodynamic properties of NH4+ fixation in manured loess soil in Shaanxi Province, China. Pedosphere. 7(1): 49-58.
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