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Simultaneous Measurement of Soil Microbial Nitrogen, Carbon, and Carbon Isotope Ratio
Author(s) -
Bruulsema T. W.,
Duxbury J. M.
Publication year - 1996
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1996.03615995006000060025x
Subject(s) - kjeldahl method , soil water , agronomy , nitrogen , chemistry , soil carbon , biomass (ecology) , carbon fibers , soil test , isotopes of nitrogen , crop , growing season , environmental chemistry , environmental science , soil science , mathematics , biology , organic chemistry , algorithm , composite number
Methods used for analysis of soil microbial biomass N and C are limited in precision and are time consuming. A method involving direct combustion of evaporated soil extracts was developed for use with an automated nitrogen and carbon analyzer (ANCA). The objectives of this study were to: (i) evaluate the usefulness of ANCA determination of microbial C and N, and (ii) ascertain whether the microbial C isotope ratios determined by the ANCA method would reflect C contributions from actively growing crops of wheat ( Triticum aestivum L.) and maize ( Zea mays L.) differing in C isotope ratio. Cropped and fallow soils were sampled at planting, anthesis, and maturity. Field‐moist soils were fumigated with chloroform and extracted with 0.05 M K 2 SO 4 for the ANCA method and with 0.5 M K 2 SO 4 for Kjeldahl analysis. Small volumes of the 0.05 M K 2 SO 4 extracts were evaporated on cone‐shaped tin disks that were analyzed using combustion at 1700°C and mass spectrometry. Reproducible values for C, N, and δ 13 C were obtained with less effort than that typically expended for Kjeldahl N analysis of similar extracts. Temporal changes in microbial δ 13 C occurred in both cropped and fallow soils during a single growing season. At maturity of the maize crop, an estimated 23% of the soil microbial C was derived from the plant material of the current maize crop. Carbon contribution from the wheat crop to the soil microbial biomass was not detected. Further refinements in the ANCA method may make the procedure routinely usable for enhancing the understanding of chloroform labile C and N as indicators of microbial dynamics in the soil.