Spatial variation of CO2 fluxes in corn and soybean fields

Authors: Hatfield, Jerry; Parkin, Timothy

Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2012
Publication Date: 12/17/2012
Citation: Hatfield, J.L., Parkin, T.B. 2012. Spatial variation of CO2 fluxes in corn and soybean fields. Agricultural Sciences. 3:986-995.

Interpretive Summary: Soil management practices have been suggested as a method of storing carbon from the atmosphere into the soil and reducing the concentration of carbon dioxide in the atmosphere. A variety of methods have been proposed ranging from adoption of reduced tillage practices to changing cropping systems. However, the concern is over how to measure the change in carbon content of the soil or the release of carbon dioxide from the soil. To address this problem we conducted a study to evaluate the variation in carbon dioxide emissions from both corn and soybean canopies at regularly spaced intervals along transects in a production field. These measurements were made weekly in each field in an area with and without plants. Although, there was a change in the soil properties along the transect there was no definable pattern to these changes suggesting that measurements could be randomly collected with a given soil type to measure the effects of different management practices. This information will be of value to other scientists and to individuals attempting to understand the effectiveness of soil management practices on carbon dioxide.

Technical Abstract: Spatial variation of soil carbon dioxide (CO2) flux during a growing season within corn and soybean canopies has not been quantified. These cropping systems are the most intense in the United States and the potential for carbon (C) sequestration in these systems through changes in soil management practices create an opportunity for reduction in greenhouse gas emissions; however, the need to understand the variation in fields is critical to evaluating changes in management systems. A study was designed to evaluate the spatial variation in soil CO2 fluxes along two transects in corn and soybean fields. Samples were collected every 5 m along a 100 m transect between the rows of the crop and also along a transect in which the plants had been removed to reduce the potential of root respiration. Soil CO2 fluxes were collected at each position with air temperature, soil temperature at 0.05 m, and soil water content (0-0.06 m). At the end of the season, soil samples for the upper 0.1 m were collected for soil organic C content, pH, sand, silt, and clay contents. On each day measurements were made, the observed CO2 emissions were scaled by dividing the CO2 flux at each position by the mean CO2 flux of the entire transect. Observed CO2 fluxes were significantly larger in the row than in the fallow position for both crops. There were no differences between the corn and soybean fallow transects; however, the corn row samples were larger than the soybean row samples. No consistent spatial patterns were observed in the CO2 fluxes nor any of the soil properties over the course of the study. When the CO2 flux data were combined over the season, there was a significant spatial pattern in the fallow transects for both crops but not for the row transects. Sampling for CO2 flux values in cropping systems has to consider the presence of a crop canopy and the amount of root respiration.