Effect of Ammonium Fixation on Determination of N Mineralized from Soil Microbial BiomassEnglish Full Text

YIN SHIXUE; TANG YAN; LIANG YONGCHAO and FENG KE(Department of Agronomy, Agricultural College, Yangzhou University, Yangzhou 225009 ,China)(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 thisstudy to extalne the effect of ammonium fixation on the determination of N mineralised from soil ndcrobialbiomass. organism suspellsioll was quantitatively introduced to Soil 1 at various rates. Both fumigation-incubation （FI） and fumigation-ext raction （FE ） met hods were used to t reat t he soil. The amount of ffeedNH4+-N increased with increasing rate of organism-N addition. A close correlation was found between theamoun of fixed aznmonium and the rate of organism-N addition. The net increso of fixed NH4+-N wereequivalent to 38% and 12% of the added organism-N for FI and FE treatments, respectively in this specificsoil. 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 and2 respectively; while in FE treatment, 9 mg N kg-1 of labelled N was found in the fraction of fixed NH4+-Nin 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 addedwas easily mineralized and nitrified. A mean of 0.64 for KN value, the fraction of N ndneralized in the killedmicrobial biomass, was obtained with inclusion of the net increase of fixed NH4+-N. The corresponding valuecalculated with exclusion of the net increase of fixed NH4+-N was 0.46. It was concluded that ammniumfixation 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 ammoniumprocess than that by FI method.

Keywords：

ammonium fixation; fumigated soil; microbial biomass N;

Series：
(D) Agriculture
Subject：
Fundamental Science of Agriculture; Agronomy
Classification Code：
S154

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Effect of Ammonium Fixation on Determination of N Mineralized from Soil Microbial BiomassEnglish Full Text

YIN SHIXUE; TANG YAN; LIANG YONGCHAO and FENG KE(Department of Agronomy, Agricultural College, Yangzhou University, Yangzhou 225009 ,China)(College of Natural Resourees and Environmental Science, Nanjing Agricultural University, Nanjing 210095,China)

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