Soil organic Carbon and Nitrogen storage estimated with the root-zone enrichment method under conventional and conservation land management across North Carolina

Authors: Franzluebbers, Alan

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2022
Publication Date: 2/6/2023
Citation: Franzluebbers, A.J. 2023. Soil organic Carbon and Nitrogen storage estimated with the root-zone enrichment method under conventional and conservation land management across North Carolina. Journal of Soil and Water Conservation. 78:124-140. https://doi.org/10.2489/jswc.2023.00064.
DOI: https://doi.org/10.2489/jswc.2023.00064

Interpretive Summary: Soil organic matter is an important attribute that contributes to soil fertility on the farm, as well as a potential sink for atmospheric carbon dioxide via soil carbon sequestration. The historic loss of soil organic matter from exploitive tillage management now offers the southeastern US an opportunity to sequester carbon with conservation management systems. An ARS scientist in Raleigh North Carolina collected soil from different land uses on 25 research stations across North Carolina to determine the potential of surface soil to store carbon from conservation management with either no-till cropping, grassland management, or timber production. The results suggested that indeed conservation management was a beneficial strategy to improve soil organic carbon and total soil nitrogen of surface soils throughout North Carolina. Soil texture was an important co-factor but did not negate the positive impact of conservation management anywhere in the state. Woodland and grassland management were more effective at storing carbon and nitrogen than no-till cropland. These results will be important for agricultural advisors, farmers, extension specialists, and scientists in the region to promote more efficient, carbon-storing practices for agriculture to simultaneously meet the production and environmental demands needed to achieve a sustainable future.

Technical Abstract: Agriculture is a globally dominating land use, so efforts to restore soil organic carbon (C) and nitrogen (N) lost through historical degradation could have enormous benefits to production and the environment, particularly by storing an organic reserve of nutrients in soil and avoiding the return of a small portion of biologically cycling C to the atmosphere. Estimates of soil organic C and N storage from conservation agricultural management are still limited when considered in proportion to the large diversity of environmental and edaphic conditions. A study was undertaken to determine the total, baseline, and root-zone enrichment stocks of soil organic C and N as affected by land use on 25 research stations distributed throughout North Carolina. Root-zone enrichment of organic matter is that portion influenced by contemporary management, and baseline is that portion dominated by pedogenesis. These fractions were compared with more traditional estimation procedures. Soil organic C and N were strongly negatively associated with sand concentration. Although physiographic region influenced overall soil C and N contents, variations in soil type and research station management within a region were equally influential. Soil organic C and N stocks were strongly affected by land use, which did not interact with the soil textural effect. Across the 25 research station locations, root-zone enrichment of soil organic C followed the order (p < 0.01) conventional-till cropland (11.1 Mg C ha^-1) < no-till cropland (21.5 Mg C ha^-1) < grassland (29.6 Mg C ha^-1) < woodland (38.6 Mg C ha^-1). Root-zone enrichment of total soil N followed a similar order, except grassland and woodland effects were reversed. Root-zone enrichment provided an integrated soil-profile assessment and a more targeted response of soil organic C and N change than did more traditional paired land use approaches, primarily due to separation of a variable pedogenic influence among sites. These point-in-time results gave a clear indication that conservation agricultural management approaches will foster surface soil organic C and N restoration across a diversity of soil types in the southeastern United States.