Predicting soil organic carbon from loss-on-ignition across four regions of Nebraska

Authors: Baker, Trinity; KAISER, MICHAEL - University Of Nebraska; TURK, JUDY - University Of Nebraska

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2023
Publication Date: 5/31/2023
Citation: Baker, T.J., Kaiser, M., Turk, J.K. 2023. Predicting soil organic carbon from loss-on-ignition across four regions of Nebraska. Communications in Soil Science and Plant Analysis. 54(16):2301-2312. https://doi.org/10.1080/00103624.2023.2217841.
DOI: https://doi.org/10.1080/00103624.2023.2217841

Interpretive Summary: Soil organic carbon is a property that has been shown to be impacted by land-use and has the ability to help buffer climate change with proper soil management. Despite the multiple benefits of organic carbon to soil, getting these values can be both costly and time consuming. This study analyzes the relationship between soil organic carbon and soil organic matter in four different regions across the state of Nebraska. Soil organic matter values are obtained through a process called loss-on-ignition. This process is a quicker and cheaper method used across the state at various different soil testing labs to obtain soil organic mattter values. The results of this study found that the relationship between soil organic carbon and soil organic matter in these regions varied by depth. Some caution should be taken for soils within major land resource area 67. Here the little to no correlation was found with depth due to high levels of volcanic ash. The relationships found in this study can be used to estimate soil organic carbon amounts by using the easier and cheaper method to obtain soil organic matter values.

Technical Abstract: Soil organic carbon (SOC) is a dynamic property that is a key indicator of soil management effectiveness within efforts towards climate change mitigation. This study was conducted to create locally-informed equations for predicting SOC from loss-on-ignition (LOI) analysis. Soils samples were collected from four counties across Nebraska. Total carbon, inorganic carbon, and LOI were analysed in the lab, and SOC was calculated as the difference between total and inorganic carbon. Locally-trained equations relating SOC and LOI were evaluated and the accuracy of predictions was assessed. Predictions were compared to those made using the van Bemmelen factor, which estimates that all soil organic matter is 58% SOC. Linear relationships were observed between SOC and LOI, and were found to be weaker in western Nebraska (R2 = 0.59), compared to central and eastern parts of the state (R2 = 0.93). Predictions were more accurate using the locally-trained predictions (RMSE = 0.05-0.13) compared to the van Bemmelen factor (RMSE = 0.30-0.53), and were further improved by developing separate equations for surface (0-25 cm) and subsurface (25-180 cm) soils (RMSE = 0.02 to 0.07). Locally-trained, depth-specific predictive equations can be used to improve the accuracy of SOC analysis using the routine LOI analysis.