Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2009
Publication Date: 2/25/2010
Publication URL: http://hdl.handle.net/10113/41303
Citation: Liebig, M.A., Tanaka, D.L., Gross, J.R. 2010. Fallow Effects on Soil Carbon and Greenhouse Gas Flux in Central North Dakota. Soil Science Society of America Journal. 74(2): 358-365. Interpretive Summary: Among the management options available to agricultural producers in the northern Great Plains, the use of fallow has persisted despite documented drawbacks of reduced precipitation-use efficiency and impaired soil quality compared to annually cropped land. In fact, fallow periods are common throughout the region due to absence of consistent precipitation, and may occupy up to 35% of cropland area in any given year. Given the prevalence of this critical non-cropping phase, a study was undertaken to contrast fallow phases in two no-tillage cropping systems in central North Dakota for their effects on soil organic carbon and greenhouse gas flux. One cropping system possessed a traditional 19 month fallow period (spring wheat – fallow), while the other incorporated a rye cover crop during the non-cropping period [spring wheat – safflower – fallow (Rye)]. Soil samples collected prior to initiation of gas flux measurements indicated no difference in organic carbon between cropping systems in the surface four inches of soil. Furthermore, cumulative fluxes of carbon dioxide, methane, and nitrous oxide did not differ between the two cropping systems, suggesting there was no net greenhouse benefit from incorporating a rye cover crop during the fallow phase. Future investigations may seek to evaluate the effects of other cover crops (or cover crop mixtures) on soil organic carbon and emission of nitrous oxide, two variables that largely dictate the greenhouse gas balance of dryland cropping systems.
Technical Abstract: Inclusion of cover crops during fallow (i.e., green fallow) may mitigate greenhouse gas (GHG) emissions from dryland cropping systems. An investigation was conducted to quantify the effects of chemical- and green-fallow on soil organic carbon (SOC) and carbon dioxide, methane, and nitrous oxide flux within spring wheat (Triticum aestivum L.) – fallow (SW-F; chemical fallow) and spring wheat – safflower (Carthamus tinctorius L.) – rye (Secale cereale L.) [SW-S-F (Rye); green fallow] under no-tillage management in west-central North Dakota. Using static chamber methodology, flux measurements were made over 19 months during the fallow period of each cropping system. Soil samples collected prior to initiation of flux measurements indicated no difference in SOC in the surface 10 cm between cropping systems. Profiles of GHG flux in the fallow phases of SW-F and SW-S-F (Rye) generally followed expected trends. However, differences in gas flux between cropping systems were few. Emission of carbon dioxide was greater under green-fallow than chemical-fallow during spring thaw until termination of rye (P=0.0071). Uptake of atmospheric methane was the dominant exchange process during the evaluation period, and was significantly (P=0.0124) greater under chemical-fallow (-2.7 g CH4-C/ha/d) than green-fallow (-1.5 g CH4-C/ha/d) following termination of rye. Fluxes of carbon dioxide, methane, and nitrous oxide did not differ between the chemical- and green-fallow phases over the 19 month period (P=0.1293, 0.2629, and 0.9979, respectively). Results from this evaluation suggest there was no net GHG benefit from incorporating a rye cover crop during the fallow phase of a dryland cropping system under no-tillage management.