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Title: Temporal dynamics of total and particulate organic carbon and nitrogen in cover crop grazed cropping systems

item Franzluebbers, Alan
item Stuedemann, John

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2014
Publication Date: 8/6/2014
Citation: Franzluebbers, A.J., Stuedemann, J.A. 2014. Temporal dynamics of total and particulate organic carbon and nitrogen in cover crop grazed cropping systems. Soil Science Society of America Journal. 78:1404-1413.

Interpretive Summary: Soil organic carbon and total soil nitrogen are key determinants for evaluating the most beneficial agricultural management practices to address climate change, environmental quality, and soil productivity issues. A scientist at the Plant Science Research Unit in Raleigh, North Carolina teamed with a former scientist in USDA-Agricultural Research Service from Watkinsville, Georgia to evaluate the effects of tillage and cover crop management on soil compaction and carbon and nitrogen concentrations in surface soil with seven years of continuous management. Grazing of winter cover crops by cow/calf pairs did no cause soil compaction, nor did it affect soil organic matter concentrations. Soil organic carbon was sequestered with time under both disk tillage and no tillage, because of the large input of crop residues with double / cover cropping. However, sequestration of soil carbon was greater with no tillage than with disk tillage due to lack of soil disturbance that can stimulate decomposition. Conservation management of soil with no tillage and periodic utilization of cover crop forage for cattle grazing can be considered appropriate adaptation strategies to climate change to increase the resilience of agriculture in the southeastern USA. Findings from this study will be important for producers to understand the value of tillage management on soil organic matter, as well as for conservation organizations and government agencies wanting to promote conservation practices to sequester carbon from the atmosphere and avoid transport of nitrogen from agricultural fields.

Technical Abstract: Soil organic C and N are important indicators of agricultural sustainability, yet numerous field studies have revealed a multitude of responses in the extent and rate of change imposed by conservation management, and therefore, a lack of clarity on responses. We conducted an evaluation of total and particulate organic C and N on a Typic Kanhapludult in northern Georgia during 7 years of tillage (conventional disk and no tillage) and cover crop management (ungrazed and grazed by cattle). Soil organic C and total soil N were greater under no tillage (NT) than under conventional tillage (CT) at depths of 0-3 and 3-6 cm, but were lower under NT than CT at depths of 12-20 and 20-30 cm. Total soil N accumulated with time under both tillage systems, but at a greater rate under NT than under CT only at a depth of 0-6 cm (0.039 vs 0.021 Mg N/ha/yr, p = 0.10). Soil organic C accumulated with time under all management systems, but there was a significant tillage x cover crop interaction at a depth of 0-6 cm (0.68 and 1.09 Mg C/ha/yr with ungrazed cover crop management under CT and NT, respectively, and 0.84 and 0.66 Mg C/ha/yr with grazed cover crop management under CT and NT, respectively). At a depth of 0-30 cm, only the tillage effect was significant (1.00 and 1.59 Mg C/ha/yr under CT and NT, respectively; p = 0.09). Particulate organic C was more dramatically different between tillage regimes at a depth of 0-30 cm (-0.49 and 0.35 Mg C/ha/yr under CT and NT, respectively; p < 0.001). Grazing of cover crops had little negative impact on soil C and N fractions, suggesting that NT and grazing of cover crops could provide a broader-spectrum conservation cropping approach in the southeastern USA.