Quantifying organic carbon stocks using a stereological profile imaging method to account for rock fragments in stony soils

Authors: JIANG, ZHOUDONG - Shenyang Agricultural University; WANG, QUIBING - Shenyang Agricultural University; BRYE, KRISTOFOR - University Of Arkansas; Adhikari, Kabindra; SUN, FUJUN - Shenyang Agricultural University; SUN, ZHONGXIU - Shenyang Agricultural University; CHEN, SI - Shenyang Agricultural University; Owens, Phillip

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2020
Publication Date: 12/3/2020
Citation: Jiang, Z., Wang, Q., Brye, K.R., Adhikari, K., Sun, F., Sun, Z., Chen, S., Owens, P.R. 2020. Quantifying organic carbon stocks using a stereological profile imaging method to account for rock fragments in stony soils. Geoderma. 385:114837. https://doi.org/10.1016/j.geoderma.2020.114837.
DOI: https://doi.org/10.1016/j.geoderma.2020.114837

Interpretive Summary: Accurately and comprehensively estimating the soil organic carbon stock for stony soils is critical for the global C stock estimation as related to global climate change. Rock fragments occupy volume in soils and therefore should be subtracted from total soil organic carbon stock. The assessment of SOC stock requires 3-D representation of the rock fragments volume and quantity. Standard methods for aquirirng rock fragment content is through visual estimation or extraction and measurement in the laboratory. The visual method is not very precise or repeatable whereas the lab measurements are time-consuming and costly. Therefore, a stereological-coupled profile imaging method method was developed using photographs from a standard digital camera. The profile imaging method performed as well as laboratory measurements and can be a rapid, accurate and repeatable method for estimating rock fragments for subtraction in soil organic stocks.

Technical Abstract: Accounting for soil organic carbon (SOC) stock in stony soils is critical for estimating global SOC stocks. However, accurate and cost-effective assessments of organic C stocks in stony soil profiles remain challenging due to the difficulties in accurately determining the volume fraction of rock fragments (RFs). The objective of this study was to develop a stereological profile imaging method for RF volume fraction estimation and SOC stock assessment in stony soil profiles. Three soil profiles with different RF lithologies, concentrations, and distributions were imaged and quantitatively sampled. The RF concentrations of three profiles were determined by visual estimation (VE), direct measurement (DM), profile imaging (PI), and stereological profile imaging (SPI). The SPI method reproduced consistent estimation of the 3-dimensional RF number density distribution and volume fraction varying with RF size compared to DM in the three profiles. The SOC stocks of three stony profiles estimated by VE, PI, and SPI methods were also assessed and compared relative to DM. Compared to DM, the average difference in accumulated SOC stock in the three profiles for the VE, PI, and SPI methods was 3.2, 1.7, and 0.9 Mg·ha-1, respectively. The accumulated profile SOC stock for profile 2 (P2) differed for the VE and PI methods, but estimated SOC stock from the SPI did not differ from DM for the three profiles. Results also showed that the differences in SOC stock assessment between RF estimation method increased with increasing RF concentrations. The SPI method was less affected by RF concentration and was more stable compared to the VE and PI methods. The stereological profile imaging method was demonstrated to be a reasonably accurate method for the quantification of RF number density distribution, volume fraction, and SOC stock in stony soil profiles.