氨固定对土壤微生物生物量氮矿化测定的影响

Two soils with relatively high(Soil 1)and low(Soil 2) ammonium fixation capacities were used in this study to examiune 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^ increased with increasing rate of organism-N addition.A close correlation was found between the amount of fixed ammonium and th rate of organism-m addition.The net increases of fixed NH4^ -N were equivalent to 38% and 12% of the added organism-N for FI and FE treatments,rspectively,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 3mg N kg^-1 of labelled N were found in the fraction of fixed NH4^ -N in Soile 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,as obtained with inclusion of the net increase of fixed NH4^ -N,The corresponding value calculated with exclusion of the net increase of ficed NH4^ -N was 0.46 ,It was concluded that ammonium fixation was a problem in deterination of KN,particularly for soils with a high ammonium fixation capacity, Results also showed that microbial biomass N measurement by FFE method was less affected by ammonium process than that by FI method.

Effect of ammonium fixation on determination of N mineralized from soil microbial biomass

Two soils with relatively high(Soil 1)and low(Soil 2) ammonium fixation capacities were used in this study to examiune 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^ increased with increasing rate of organism-N addition.A close correlation was found between the amount of fixed ammonium and th rate of organism-m addition.The net increases of fixed NH4^ -N were equivalent to 38% and 12% of the added organism-N for FI and FE treatments,rspectively,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 3mg N kg^-1 of labelled N were found in the fraction of fixed NH4^ -N in Soile 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,as obtained with inclusion of the net increase of fixed NH4^ -N,The corresponding value calculated with exclusion of the net increase of ficed NH4^ -N was 0.46 ,It was concluded that ammonium fixation was a problem in deterination of KN,particularly for soils with a high ammonium fixation capacity, Results also showed that microbial biomass N measurement by FFE method was less affected by ammonium process than that by FI method.