Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2012
Publication Date: 11/23/2012
Citation: Liebig, M.A., Kronberg, S.L., Hendrickson, J.R., Doug, X., Gross, J.R. 2012. Carbon dioxide efflux from long-term grazing management systems in a semiarid region. Agriculture Ecosystems and the Environment. 164:137-144. Interpretive Summary: Grasslands represent the largest land resource in the world, and are responsible for regulating multiple ecosystem services. Limited evaluations have been undertaken in grasslands for elucidating management effects on soil CO2 efflux (i.e., soil respiration), particularly during non-growing season periods over multiple years. Understanding management effects on soil CO2 efflux is important for elucidating ecosystem contributions to the global carbon cycle. In this study, we measured soil CO2 efflux from three historical pastures at the Northern Great Plains Research Laboratory near Mandan, ND. Two pastures were composed of native vegetation with different stocking rates (moderate and heavy grazing), while the third pasture was seeded to crested wheatgrass and grazed heavily. Soil CO2 efflux rates observed in this study fell within expected ranges for temperate grasslands, but did not differ between native vegetation pastures differing in stocking rate. However, soil CO2 efflux was greater in the crested wheatgrass pasture than the native vegetation heavily grazed pasture, a result attributed to prevalence of cool-season grass and high available N in the former. Soil temperature and moisture status proved to be strongly associated with soil CO2 efflux, though associations were seasonally dependent with temperature most relevant during spring and fall and moisture status most important in summer. While increased stocking rate did not contribute to elevated soil CO2 efflux within native vegetation pastures, it is important to acknowledge the important role of weather to affect grassland productivity from year to year. Accordingly, long-term monitoring is needed to confidently discern grazing management effects on carbon dynamics.
Technical Abstract: Grazing management can affect grassland carbon (C) dynamics, yet limited information is available documenting management effects on soil carbon dioxide (CO2) efflux. A study was conducted to quantify the role of long-term grazing management to affect soil CO2 efflux within the semiarid northern Great Plains of North America. Grazing management systems evaluated in the study included two native vegetation pastures differing in stocking rate [moderately grazed pasture (MGP), heavily grazed pasture (HGP)] and a fertilized, grazed crested wheatgrass pasture (CWP) near Mandan, ND. Soil CO2 efflux was measured on one to two week intervals for three years using static chamber methodology. Supplemental assessments of soil temperature and water content, aboveground live biomass, root biomass, and soil microbial biomass C were conducted during each growing season. Soil CO2 efflux did not differ between native vegetation pastures differing in stocking rate. However, mean hourly soil CO2 efflux was greater in CWP (100 mg C/m2/h) than HGP (81 mg C/m2/h) (P=0.03), a result attributed to prevalence of cool-season grass and high available N in CWP. Soil CO2 efflux differed among grazing treatments during spring (Mar–May) and fall (Sep–Nov), but not winter (Dec–Feb) and summer (Jun–Aug). Associations between soil CO2 efflux and abiotic factors were seasonally dependent, with positive associations between efflux and soil temperature during spring (r=0.71, P<0.01) and fall (r=0.45, P<0.01) and efflux and water-filled pore space during summer (r=0.46, P<0.01). In this study, increased stocking rate did not contribute to elevated soil CO2 efflux within native vegetation pastures. Given strong weather-dependence on grassland productivity, long-term monitoring is necessary to confidently discern grazing management effects on C dynamics.