Root-zone enrichment of soil organic carbon and nitrogen under grazing and other land uses in Virginia

Authors: Franzluebbers, Alan

Submitted to: Grass and Forage Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Grazing lands are considered an appropriate conservation land use that benefits both farmer and society due to erosion control, storage of soil carbon and nitrogen, and providing open space for wildlife habitat. Pastures are typically underappreciated despite a large potential to sequester carbon and nitrogen in soil that preserves environmental quality. An ARS scientist in Raleigh North Carolina collected soil from 31 different farms in Virigina under grazing land, no-till cropland, and woodland. Results documented the large storage potential of grazing land compared with other land uses. Pasture age and stocking rate were critical factors influencing results, while stocking method, past fertilization, and low levels of hay feeding did not influence quantities of soil carbon and nitrogen. 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 for a sustainable future.

Technical Abstract: Grazing lands can be considered a conservation land use providing value to farmers and society. An underappreciated value of these lands may be in C and N storage and cycling. However, soil organic C (SOC) and total soil N (TSN) storage under humid-zone pastures have not been well characterized. In this study, a survey of 31 farms in Virginia USA characterized SOC and TSN depth distributions under a diversity of grassland management scenarios, as well as in comparison with long-term no-till cropland and woodland uses on the same farms. Root-zone enrichment calculations separated management-controlled SOC and TSN stocks from a baseline condition at 30-cm depth. Total stock of SOC at 0-30-cm depth varied from 46 to 88 Mg C/ha (5 to 95% range from 304 soil profiles) across all land uses. Root-zone enrichment of SOC was maximized with mature pastures (>20 years old) at 38.3 +/- 1.6 Mg C/ha, which was not different from that under woodland (39.8 +/- 1.2 Mg C/ha), but was greater than under no-till cropland (28.3 +/- 1.3 Mg C/ha) and conventional-till cropland (15.1 +/- 5.1 Mg C/ha). Root-zone enrichment of TSN was optimized at stocking rate of ~1 Mg live weight ha-1, but was not affected by stocking method, N fertilization history, or low levels of hay feeding. These results suggest that well-managed grazing systems in Virginia are storing significant amounts of SOC and TSN, with at least half due to management-induced compared with pedogenic-controlled accumulation.