Pedosphere 7(2): 127--132, 1997
ISSN 1002-0160/CN 32-1315/P
©1997 Soil Science Society of China
Published by Elsevier B.V. and Science Press
| Effect of ammonium fixation on determination of N mineralized from soil microbial biomass |
| YIN Shi-Xue1, TANG YAN1, LIANG Yong-Chao2 and FENG KeE1 |
1 Department of Agronomy, Agricultural College, Yangzhou University, Yangzhou 225009 (China);
2 College of Natural Resourees and Environmental Science, Nanjing Agricultural University, Nanjing 210095 (China) |
| ABSTRACT |
| Two soils with relatively high (Soil 1) and low (Soil 2) ammonium fixation capacities were used in this study to examine the effect of ammonium fixation on the determination of N mineralized from soil microbial biomass. Organism suspension was quantitatively introduced to Soil 1 at various rates. Both fumigation-incubation (FI) and fumigation-extraction (FE) methods were used to treat the soil. The amount of fixed NH4+-N increased with increasing rate of organism-N addition. A close correlation was found between the amount of fixed ammonium and the rate of organism-N addition. The net increases of fixed NH4+-N were equivalent to 38% and 12% of the added organism-N for FI and FE treatments, respectively, in this specific soil. To provide isotopic evidence, 15N-labelled organism-N was added to Soils 1 and 2 at 121.4 mg N kg-1. In FI treatment, 22 and 3 mg N kg-1 of labelled N were found in the fraction of fixed NH4+-N in Soils 1 and 2 respectively; while in FE treatment, 9 mg N kg-1 of labelled N was found in the fraction of fixed NH4+-N in Soil 1 only. There was no labelled N in the fraction of fixed NH4+-N in Soil 2. In all of the unfumigated (check) soils, there was little or no labelled N in the fixed fractions, probably because the organism-N added was easily mineralized and nitrified. A mean of 0.64 for KN value, the fraction of N mineralized in the killed microbial biomass, was obtained with inclusion of the net increase of fixed NH4+-N. The corresponding value calculated with exclusion of the net increase of fixed NH4+-N was 0.46. It was concluded that ammonium fixation was a problem in determination of KN, particularly for soils with a high ammonium fixation capacity. Results also showed that microbial biomass N measurement by FE method was less affected by ammonium process than that by FI method. |
| Key Words: ammonium fixation, fumigated soil, microbial biomass N |
| Citation: Yin, S. X., Tang, Y., Liang, Y. C. and Feng, K. 1997. Effect of ammonium fixation on determination of N mineralized from soil microbial biomass. Pedosphere. 7(2): 127-132. |
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