ARS | Publication request: Carbon dioxide emissions in fallow periods of a corn-soybean rotation: eddy-covariance versus chamber methods

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2009
Publication Date: February 20, 2009
Citation: Hernandez Ramirez, G., Parkin, T.B., Hatfield, J.L., Sauer, T.J., Prueger, J.H. 2009. Carbon dioxide emissions in fallow periods of a corn-soybean rotation: eddy-covariance versus chamber methods [abstract]. North American Carbon Program Meeting (NACP)-February 17-20, 2009 in San Diego, CA. Available: http://www.nacarbon.org/cgi-bin/meeting_2009/mtg2009_ab_search.pl?action=3&ab_id=41

Technical Abstract: Carbon dioxide (CO2) fluxes at terrestrial surface are typically quantified using eddy-covariance (EC) or chamber (Ch) techniques; however, long-term comparisons of the two techniques are not available. This study was conducted to assess the agreement between EC and Ch techniques when measuring CO2 flux during fallow periods of a corn-soybean rotation. From 2004 to 2007, we quantified CO2 fluxes by both continuous EC and hourly Ch measurements. One flux station and at least two automated soil chambers were permanently deployed in both corn and soybean fields. In November and December, cumulative CO2 efflux by EC method was roughly 1.5-fold greater following corn crop than after soybean (37.1 ± 5.0 vs. 24.8 ± 7.2 g C m-2), whereas the period from January to April showed no differences across crops and years (78 ± 6 g C m-2). This initial difference in the late fall period may be explained by both greater residue production from corn than soybean and fall tillage of the corn field. When contrasting EC to Ch measurements for November and December of 2004, we observed 18% greater cumulative CO2 effluxes with Ch (54.3 vs. 45.9 g C m-2). However, this disagreement was not evenly distributed throughout these two months. The comparison of daily CO2 fluxes by the two techniques revealed episodic patterns of disagreement with 42% (3.5 g C m-2) of the total disagreement concentrated within five consecutive days in late November. This episodic pattern of high disagreement occurred shortly after both the fall tillage operation and a major rainfall event (20 mm d-1). Both unaccounted-for three-dimensional advective CO2 fluxes in EC and soil microclimate modification by Ch may partly explain disagreement between the two techniques. Use of different methods to quantify CO2 fluxes need to be evaluated carefully to understand the spatiotemporal patterns of the differences.