Liebig, Mark (USDA-ARS, P.O. Box 459, Mandan, ND, 58554; Phone: 701-667-3079; Fax: 701-667-3054; Email: email@example.com)
M. A. Liebig*, S. L. Kronberg, J. R. Gross, J. D. Hanson, A. B. Frank, R. L. Phillips
Grazing management systems affect agroecosystem sustainability through impacts on soil condition. We investigated the effects of long-term (over 70 yr) grazing on soil properties and N2O emission within a moderately-grazed pasture (MGP), heavily-grazed pasture (HGP), and a fertilized crested wheatgrass (Agropyron desertorum (Fisch. ex. Link) Schult.) pasture (FCWGP) near Mandan, ND. Grazing-induced changes in species composition and N fertilizer application contributed to differences in soil properties and N2O emission among pastures. Soil organic C (SOC) was 5.7 Mg ha-1 greater in FCWGP and HGP than MGP at 0 to 5 cm, whereas HGP had 2.4 Mg ha-1 more SOC than FCWGP and MGP at 5 to 10 cm. At 30 to 60 cm, SOC in FCWGP was 4.0 and 7.5 Mg ha-1 greater than in HGP and MGP, respectively. Particulate organic matter (POM) C and N in the surface 5 cm of FCWGP were three- and five-fold greater, respectively, than in HGP and MGP. Acidification from N fertilization in FCWGP decreased soil pH and exchangeable Ca and Mg compared to HGP and MGP in the surface 5 cm. Annual nitrous oxide emission was over three-fold greater in FCWGP compared to HGP and MGP, and was positively associated with POM-C across all pastures (r=0.92; P=0.0001). Results from this study suggest fertilized crested wheatgrass enhances deep storage of SOC, but contributes to surface acidification and greater N2O emission relative to native vegetation pastures in the northern Great Plains.