N 2 O 15 N NH + NH 3 Rittenberg mg mmol L - 1 CuSO mg. 10 mol L. Pre-Concentration device PreCon

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1 50 1 Vol. 50 No ACTA PEDOLOGICA SINICA Jan N 2 O * N N 2 O N 2 O N N 2 O N N 5 ~ 20 μg N N 2 O N S8. 3 A N N 2 O N N N NO - 3 NO - 2 N N N MgO NH 3 Rittenberg 1 Dumas N 1 2 N N 2 O NO - 2 NO N N 2 O NO - 2 N N 2 O Cu ~ ph N 1. 5 mg 2 O N 0. 5 mmol L - 1 CuSO mg NO - 3 NO - 2 NO - 3 NO - NH 2 3 NaOBr NaOH 10 mol L NO - 3 -N 2-3 N 2 O ph. 7 NO - 3 Pre-Concentration device PreCon NO - 2 NH 2 OH NO - 2 CF-IRMS NH 2 OH N 2 O2 h N N 2 O NO - 3 * yccao@ issas. ac. cn

2 11 50 N N 2 O N 2 O N 2 O 1. 3 NO - 2 -N Hydroxylamine N 2 O HNO 2 + NH 2 OH N 2 O + 2H 2 O 7 ph ph h N N- N N 2 O N 10 μmol N 2 O 99 atom% N N 1 / atom% N N 2 O N N N N N 2 O N N N atom% N 5. 6 atom% N N atom% NO - 2 = 2 N atom% N 2 O atom% CuSO 5H 2 O 0. 5 mmol L - 1 N - Thermo Finnigan ml 100 μg N 2 PreCon MAT ml 2. 5 ml 100 ml 2 N 6 1. atom% 0. 6 atom% ml 100 μg ISODAT NT N N N ml N 2 O Cup Cup3 Cup m /z 1 N 1 N 16 O μg N m /z 5 1 N N 16 O + m /z 6 1 N 1 N 18 O + m /z 5 m /z N 2 O N 5. 2 atom% N N δ N atom% N 2 O atom% 250 ml 2 mol L - 1 KCl N 2 O ml 50 μg N 1 SHOKO N 2 O mg AR 250 ml 2 mol L - 1 N 2 O δ N Air ± Air δ N N 2 O N 2 O δ N Air NH 2 OH N N 2 O δ N N atom% N 2 O N N mg N 5. 6 atom% 100 ml CuSO 5H 2 O 0. 5 mmol L - 1 ml 100 μg N mg A. R 250 ml N mg N 5. 2 KCl ml 50 μg N N ml 30 s ml 100 ml 2 N 2 O 2 N 1. 5 atom% 235 s N 2 O atom% ml 50 μg N N

3 1 N 2 O N N 5 ml 0. 01mol L ml 5 min 2 ~ 3 1 ml μg N 90 N 90 N atom% N N 1 ml 10 mol L - 1 NaOH mg N ml atom% 100 ml 2 mol L - 1 KCl N 2 O 100 ml 1 μg N atom% N mg AR mol L ml 2 mol L - 1 KCl 1 mol L mol L - 1 ph ml 1 μg N N ~ ml ml 100 ml 25 ml 2 mol L - 1 KCl 2. 5 ml 2 N 0. 2 mol L min 1. 5 atom% 0. 5 atom% ml 1 μg N NO - 2 N 2 50 ml N 1 50 mg 5 ml 1 mol L N mol L ml μg N 20 ~ 25 ml NO N 120 r mim h 100 ml N 1 2 O N atom% 2 60 g mol L - 1 HCl 250 ml kg 50 mg N N atom% 0. 0 mol L - 1 NH N 2 OH HCl 20 ml 50% d 3 N 50 ml ml 2 mol L - 1 KCl 1 ml 1 mol L - 1 HCl 1 h 0. 5 ml 0. 0 mol L - 1 NH 2 OH HCl r mim h 2. N 2 O 100 ml N 2 O N 2 O N atom% mol L mmol L - 1 CuSO 5H 2 O MgO ~ mol L N 2 O Laughlin NaOBr 20 ~ 25 ml 0. 2 g MgO Cu 2 + N 2 O

4 N 2 O Cu μl L - 1 NaOBr N 2 O mmol L - 1 Cu 2 + NaOBr 10 mol L - 1 Table 1 25% N 2 O 3. 2 N NH + N 2 CV < 1% N 10 μg - 1 N N 20 μg - 1 Cu μl L - 1 Cu mmol L - 1 N 2 O N N 2 O NaOBr 3 Hauek 8 NaOBr 5 mol L - 1 1% ~ N 2 O -N N 3% N 2 O 1 -N 2 N 2 O Effects of alkalinity of NaOBr on N 2 O production rate μl L - 1 NaOBr Alkalinity of NaOBr 5. 0 mol L mol L N 2 O -N N Table 2 Accuracy and precision of the determination of N abundance of -N by N 2 O produced Reference value N 2 O N atom% N atom% in N 2 O Measurement value Average value CV % N 2 O ph. 7 NO - 3 NO - 2 NH 2 OH N 2 O2 h ph 8 ~ 9 3 N 2 O ph. 7 NO - 3 N 2 O N 2 O 1

5 1 N 2 O N Table 3 Cd-Cu NO - 3 N 2 O Effects of amount of copperized cadmium added on Table NO - 3 N 2 O Effects of sequence of the addition of two reagents on production of N 2 O from NO - 3 Cd-Cu Cd-Cuadditional amounts mg time - 1 N 2 O Concentration of N 2 O produced μl L NO - 3 production of N 2 O from NO Sequence 1 μl L Sequence 2 μl L N N 2 O NO - 3 NO - 3 N 10 μg N 2 O N NO Cd-Cu NO - 3 ph. 7 2 Cd-Cu ph. 7 Notes Sequence 1 add Cd-Cu pellets into NO - 3 solution vacuumize the container and then add ph. 7 buffer solution Sequence 2 add Cd-Cu pellets into ph. 7 buffer solution vacuumize the container and then add NO - 3 solution 10 μg N 3. 5 N atom% CV < 1. 0% 6 NO - 2 N Table 5 5 N 2 O NO - 3 -N N Accuracy and precision of the determination of N abundance of NO - 3 -N by N 2 O produced N 2 O N atom% N atom% in N 2 O NO - 3 -N Reference value Measurement value Average value CV %

6 Table 6 6 N 2 O NO - 2 -N N Accuracy and precision of the determination of N abundance of NO - 2 -N by N 2 O produced NO - 2 -N Reference value NO - 2 -N N atom% N atom% in NO - 2 -N 1 Calculating value Average value N 2 O N N atom% Based on the measured value of N abundance of N 2 O calculate N atom% in line with the equation CV % 0. 5 μg - 1 N NO - 2 N N NO μmol - 1 N 7 μg N NO μmol N 3. 5 μg NO μg N μmol NO Soil type Table 7 7 N Content and N abundance of the three forms of nitrogen in extractions of the two soils Content N μg ml - 1 -N NO - 3 -N NO - 2 -N N N abundance 1 Content N μg ml - 1 N N abundance N N abundance Soil Soil NO - 2 -N This content include the content of NO - 2 -N

7 1 N 2 O N 119 -N NO - 3 -N N NO - 3 -N N 1 N N N 2 O N 2 O N N Chinese. Acta Pedologica Sinica N 2 O 5 Roeckmann T Kaiser J Brenninkmeijer C A M N 20 μg N 5 μg N 0. 5 μg N NO - 2 N NO - 2 NO NO Lu R K. Analytical methods for soil and agricultural chemistry In Chinese. Beijing China Agricultural Science and Technology Press Laughlin R J Stevens R J Zhuo S. Determining nitrogen- in ammonium by producing nitrous oxide. Soil Science Society of America Journal Stevens R J Laughlin R J. Determining nitrogen- in nitrite or nitrate by producing nitrous oxide. Soil Science Society of America Journal N 2 O CH CO Cao Y C Sun G Q Han Y et al. Determination of nitrogen carbon and oxygen stable isotope ratios in N 2 O CH and CO 2 at natural abundance levels by mass spectrometer In et al. Gas chromatography/ isotope-ratio mass spectrometry method for high-precision position dependent N and 18 O measurements of atmospheric nitrous oxide. Rapid Commun Mass Spectrom Roeckmann T Kaiser J Brenninkmeijer C A M The isotopic fingerprint of the pre-indus-trial and anthropogenic N 2 O source. Atmos Chem Phys Stevens R J Laughlin R J Atkins G J et al. Automated determination of nitrogen--labeled dinitrogen and nitrous oxide by mass spectrometry. Soil Science Socienty of America Journal 8 Hauck R D. Nitrogen isotope ratio analysis / / Page A L et al. Methods of soil analysis. Part 2. 2nd ed. Madison WI Agron Monogr 9. ASA and SSSA DETERMINING N ABUNDANCE IN AMMONIUM NITRATE AND NITRITE IN SOIL BY MEASURING NITROUS OXIDE PRODUCED Cao Yacheng Zhong Ming Gong Hua Lu Guoxing State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing China Abstract A new method was designed for direct determination of N abundance of NO - 3 and NO - 2 in soils with mass spectrometry. The principle of this method was based on analysis and quantification of N abundance of the N 2 O produced from NO - 3 and NO - 2 through transformation reactions catalyzed with their respective specific chemical reagents separately. The measured values of N abundance of the N 2 O tally well with their respective reference values in NO - 3 and NO - 2. The method was characterized by quickness simpleness and freedom from contamination of atmospheric nitrogen. Especially this method has a very low detection limit and 5 ~ 20 μg N in the sample is adequate for detection. Therefore it will be of a great help to study on mineralization nitrification and denitrification of nitrogen in soils. Key words Ammonium Nitrate Nitrite N 2 O N abundance Mass spectrometry