|STUEDEMANN, JOHN - Retired ARS Employee|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2011
Publication Date: 5/1/2012
Citation: Franzluebbers, A.J., Endale, D.M., Buyer, J.S., Stuedemann, J.A. 2012. Tall fescue management in the Piedmont: Sequestration of soil organic and total nitrogen. Soil Science Society of America Journal. 76:1016-1026.
Interpretive Summary: Soil quality restoration of previously degraded croplands that have been abandoned from production can occur with grassland management, because grasses stabilize the soil surface and prevent further erosion from occurring. How those grasslands are managed for optimum restoration of soil quality is an open question needing scientific support. Scientists with the USDA Agricultural Research Service in Watkinsville Georgia and Beltsville Maryland collaborated to conduct an 8-year-long investigation of how tall fescue pastures could be managed to reduce soil compaction and improve soil organic matter accumulation. Soil bulk density (the scientific measure of soil compaction) declined with time under all pasture management systems, but more so with broiler litter fertilization than with inorganic fertilization. This result could have been due to the organic amendment that helped loosen surface soil by encouraging soil animal activity and/or by promoting greater root development. Soil organic carbon and nitrogen accumulated with time under all pasture management systems, but was more so under grazed than under hayed management. This result was likely due how the forage was harvested. Cattle consumed forage on the pasture, but returned a large portion of the carbon and nitrogen back to the pasture via feces. Carbon contained in the forage cut for hay was removed from the field to be fed to animals elsewhere. No differences were detected in soil organic matter among tall fescue-endophyte associations (wild, novel, and free), nor between nutrient sources applied to fertilize pastures (inorganic and broiler litter). The results of this research have important implications for assessing soil quality of grazing lands in the eastern USA, but also for assessing the impacts of agricultural management on the potential to mitigate greenhouse gases, such as carbon dioxide.
Technical Abstract: High quality soil-surface characteristics are important for developing environmentally sustainable agroecosystems. We evaluated the factorial combination of fertilization regime (inorganic and broiler litter) and tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]-endophyte association (free, novel, and wild) with cattle grazing (plus a control treatment of inorganic+novel endophyte with haying) on surface soil compaction and soil organic C and total N sequestration during 8 yr of management on a Typic Kanhapludult in Georgia. Bulk density declined with time in the surface 12 cm of soil (-0.015 Mg/m3/yr), more so with broiler litter than with inorganic fertilizer and more so with novel or wild endophyte than with endophyte-free association. Soil organic C and total N were sequestered with time at all depth intervals to 20 cm (0-3, 3-6, 6-12, and 12-20 cm), but by far the greatest rate of sequestration occurred at a depth of 0-3 cm (1.07 and 0.050 Mg/ha/yr for C and N, respectively). At a depth of 0-6 cm (surface zone most responsive to management), soil organic C sequestration was (a) greater with grazed than with hayed management (1.36 vs 0.69 Mg C/ha/yr, respectively), (b) similar between broiler litter and inorganic fertilization, (c) similar among endophyte associations, and (d) similar among zones within a grazed pasture, although significant interactions among these treatment effects occurred due to various landscape, soil type, and/or animal behavior influences. At a depth of 0-20 cm, soil organic C and total N sequestration were not affected by treatment variables, but high mean sequestration rates of 1.51 Mg C/ha/yr and 0.126 Mg N/ha/yr during managed grazing of tall fescue in addition to the previous decade of unmanaged herbaceous fallow (implied sequestration rates of 0.76 Mg C/ha/yr and 0.062 Mg N/ha/yr) suggests that improved grazing management systems can have an enormous benefit to surface soil fertility restoration of degraded soils in the southeastern USA.