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Title: FIELD VARIABILITY OF CARBON ISOTOPES IN SOIL ORGANIC CARBON

Author
item LEAVITT, S - UNIV OF ARIZONA
item PAUL, E - MICHIGAN STATE UNIV
item PENDALL, E - UNIV OF ARIZONA
item Pinter Jr, Paul
item Kimball, Bruce

Submitted to: Nuclear Instruments and Methods in Physics Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1997
Publication Date: N/A
Citation: Leavitt, S.W., Paul, E.A., Pendall, E., Pinter Jr, P.J., Kimball, B.A. 1997. Field variability of carbon isotopes in soil organic carbon. Nuclear Instruments and Methods in Physics Research. 123:451-454.

Interpretive Summary: The carbon dioxide concentration (CO2) in the Earth's atmosphere is increasing, and predictions of consequent global warming and changing precipitation patterns have been made. However, higher levels of CO2 are also known to stimulate the growth of plants directly. Therefore as part of free-air CO2 enrichment (FACE) experiments, measurements of the effects of elevated CO2 on the growth of crops were made. In addition, by determining the isotopic ratios of the carbon in the plants and in the soil, it is possible to determine how much of the carbon in the soil organic matter came from the high-CO2-grown plants provided the signal is greater than the background soil variability. This study determined the severity of the such background variability. This research will aid in predicting the future levels of atmospheric CO2 and the extent to which the sequestration of carbon in the soil will mitigate the rate of rise, thereby slowing global change and benefitting many of earth's ecosystems and most of mankind.

Technical Abstract: Free-air CO2 enrichment (FACE) plant-growth experiments conducted in Arizona have allowed a spinoff isotope tracer experiment (tank CO2 is 14C- and 13C-depleted) to follow the input of carbon into soil organic matter pools. Accurate assessment of the 14C and 13C inputs to soils by this pathway requires detailed knowledge of the isotopic composition of the soils before the experiments. We have examined the variability of del 13C in soil organic matter in eight experimental plots prior to the beginning of the 1995-96 FACE experiments with wheat. Del 13C variability was higher immediately after harvest of a previous crop in June, but the plots were much more homogeneous five months later immediately before planting. Intervening field management, including disking, plowing, and installation of irrigation drip tape likely contributed to mixing the soils.