225-4 Prescribed Grazing and Soil Carbon Stability: Using C/N as a Proxy for Long-Term Sequestration

Session: Critical Zone Science: Intersection of Processes Linked to Geomorphology, Ecology, Fire and Climate (Posters)

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Prescribed sheep grazing is increasingly used as a sustainable land management practice in agricultural fields, conservation areas, and utility corridors due to its targeted, low-impact vegetation control. Despite its growing use, few studies have evaluated its ecological impacts in humid temperate regions such as southwest Michigan. Carbon is stored in soil as soil organic carbon, which offers insight into the health of the soil, as it contributes to moisture retention and can supply nutrients. This study examines how prescribed grazing affects soil carbon and nitrogen dynamics by using C/N ratios, %C, and %N as indicators of organic matter quality and carbon stabilization potential. Two 2-acre plots (control and grazed) in the same field were monitored seasonally from May 2024 to May 2025. Soil cores were collected at four time points to a depth of 60 cm (in 15 cm intervals), along with samples for bulk density and moisture. In the lab, soils were dispersed in sodium hexametaphosphate and passed through a 53-µm sieve to separate particulate organic matter (POM) and mineral-associated organic matter (MAOM). Each fraction was then dried, ground, and analyzed for elemental composition. Results show that POM from grazed soils had a lower average C/N ratio (26) than that of control soils (32), suggesting greater nitrogen availability and more rapid microbial processing of organic matter. This microbial transformation is a critical step in the formation of persistent carbon pools that contribute to long-term carbon sequestration. Low C/N ratios are associated with increased microbial activity, which promotes decomposition of organic matter and the formation of stable carbon pools, particularly in the MAOM fraction. While surface soils (0–30 cm) in both plots showed wide variability in C/N, deeper soils (30–60 cm) in the grazed plot exhibited a consistent decline in C/N over time, indicating deeper transformation and stabilization of organic matter in just one grazing season. These results indicate that prescribed sheep grazing may foster conditions favorable for soil carbon stabilization through enhanced microbial processing and accumulation of stable carbon pools, highlighting its potential as a nature-based climate solution for temperate agricultural systems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9971

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