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

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.

Root‐zone enrichment of soil‐test biological activity and particulate organic carbon and nitrogen under conventional and conservation land management

“…The only orthogonal contrast with statistical significance was broadly between conservation land uses (grassland and woodland) and cropland (conventional‐till and no‐till) ( p < 0.001). These associations illustrate that the factors controlling antecedent conditions of the stock of total soil N also likely controlled root‐zone enrichment of STBA, such as climatic conditions and soil texture (Franzluebbers, 2023).…”

“…The only orthogonal contrast with statistical significance was broadly between conservation land uses (grassland and woodland) and cropland (conventional-till and no-till) (p < 0.001). These associations illustrate that the factors controlling antecedent conditions of the stock of total soil N also likely controlled root-zone enrichment of STBA, such as climatic conditions and soil texture (Franzluebbers, 2023). With total soil N as the primary variable affecting rootzone enrichment of STBA and assessing variations within each land use separately, sand concentration at 0-to 30-cm depth was also an important covariate in some land use categories.…”

Climate change impacts on soil, water, and biodiversity conservation

“…Taken as a whole, the papers presented in this special issue address this call to action. The research papers share new findings related to management approaches to increase soil organic C (Kutos et al 2023;Franzluebbers 2023) and decrease N leaching (Shrestha et al 2023) in major agricultural land management systems. New knowledge about the importance of the soil microbiome points the way forward to improved systems in the future (Bell et al 2023), and the findings of Watts et al (2023) indicate that co-benefits of GHG mitigaton may be associated with conservation practices implemented for other purposes and that additional research in this area is needed.…”

“…Analysis of land use impacts on C and N from research stations across North Carolina revealed that the root zone enrichment approach allowed separation of management and pedogenisis effects (Franzluebbers 2023). Variations in soil type and management within a region were equally influential in determining soil C and N contents.…”

“…In the Research Section, two research editorials (Brown 2023;Archer et al 2023) present insights into critical concerns and paths forward for western rangelands, including the challenges of invasive annual grasses into rangelands. Research papers in this special issue synthesize findings on how climate change affects C and nitrogen (N) responses to conservation and management in rangelands (Kutos et al 2023) and croplands (Franzluebbers 2023;Shrestha et al 2023). Bell et al (2023) introduce the importance of the soil microbiome in soil processes and elucidate soil microbiome responses to temperature, moisture, and cellulose amendments, contrasting the responses in soils from a diverse, perennial prairie ecosystem and a monoculture annual corn (Zea mays L.) agroecosystem.…”