Comparison of Soil Carbon Dynamics Between Restored Prairie and Agricultural Soils in the U.S. Midwest
Creators: name: Frantal, Ian Lucas
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 410501
subject: Environmental biogeochemistry
classificationCode: 410604
subject: Soil chemistry and soil carbon sequestration (excl. carbon sequestration science)

description: Globally, soils hold more carbon than both the atmosphere and aboveground terrestrial biosphere combined. Changes in land use and land cover have the potential to alter soil carbon cycling throughout the soil profile, from the surface to meters deep, yet most studies focus only on the near surface impact (&lt; 25 cm deep). This research bias toward shallow soil carbon cycling has ramifications for understanding the full impacts of agricultural and restoration management practices on soil organic and inorganic carbon dynamics. The primary objective of my thesis research is to evaluate the factors controlling the impact of deep-rooting perennial grass on soil carbon cycling during prairie restoration of soil following long term, row crop agriculture. Paired soil pits were established to compare the effects of restoration on soil C dynamics in a corn-soy cropping system (minimal tillage) and restored prairie sites in Nebraska and Illinois. At each site, soil organic carbon (SOC) and inorganic carbon (SIC) content, stock, and stable carbon isotope analysis were preformed to ~2 m depth to assess long term integrated C dynamics. Estimating the contribution of prairie carbon inputs to the SOC in the soil profile was examined using stable carbon isotopic signatures in the SOC in relation to the above ground vegetation changes in C<sub>3</sub> and C<sub>4</sub> photosynthetic pathway plant community composition. Comparative analysis of edaphic properties and soil carbon suggests that deep loess deposits in Nebraska permit enhanced water infiltration and SOC deposition to depths of ~100 cm in 60 years of prairie restoration. In Illinois, poorly drained, clay/lime rich soils on glacial till and a younger restored prairie age (15 years) restricted the influence of prairie restoration to the upper 30 cm. Comparing the δ<sup>13</sup>C values of SOC and SIC in each system demonstrated that SIC at each site is likely of lithogenic origin. This work indicates that the magnitude of influence of restoration management is dependent on edaphic properties inherited from geological and geomorphological controls. Future work should quantify root structures and redox properties to better understand the influence of rooting depth on soil carbon concentrations. Fast-cycling C dynamics can be assessed using continuous, in-situ CO<sub>2</sub> and O<sub>2</sub> soil gas concentration changes. The secondary objective of my thesis was to determine if manual, low temporal resolution gas sampling and analysis are a low cost and effective means of measuring soil O<sub>2</sub> and CO<sub>2</sub>, by comparing it with data from in-situ continuous (hourly) sensors. Manual analysis of soil CO<sub>2</sub> and O<sub>2</sub> from field replicates of buried gas collection cups resulted in measurement differences from the continuous sensors. Measuring CO2 concentration with manual methods often resulted in higher concentrations than hourly, continuous measurements across all sites. Additionally, O<sub>2</sub> concentrations measured by manual methods were higher than hourly values in the restored prairie and less in agricultural sites. A variety of spatial variability, pressure perturbations, calibration offsets, and system leakage influences on both analysis methods could cause the discrepancy.