Soil carbon changes influenced by soil management and calculation method

Authors: Mikha, Maysoon; Benjamin, Joseph; Halvorson, Ardell; Nielsen, David

Submitted to: Open Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2013
Publication Date: 6/10/2013
Citation: Mikha, M.M., Benjamin, J.G., Halvorson, A.D., Nielsen, D.C. 2013. Soil carbon changes influenced by soil management and calculation method. Open Journal of Soil Science. 3:123-131.

Interpretive Summary: For the last five decades, soil organic carbon (SOC) content was evaluated using soil bulk density associated with a specific soil depth (fixed depth). Recently, researchers have argued that changes in soil bulk density may have unequal effect on soil mass associated with the fixed depth. This may have a confounding effect on SOC mass estimation due to different management practices. Therefore, recent research suggesting alternative methods to calculate SOC and other soil nutrients based on equivalent soil mass basis (ESM). The ESM approach will reduce the SOC error calculated in soil profiles due to changing soil bulk density under different management practices. The objective of this study is to evaluate the changes in SOC caused by two factors: (i) changing SOC concentration and (ii) changing equivalent soil mass (ESM) in comparison with fixed-depth. Further, this study calculate changes in SOC stock over time using a minimum equivalent soil mass (ESMmin) approach from a single sampling event compared with the fixed-depth scenario. In 2008, Two tillages (no-till and chisel plow), two crop rotations (multiple crop and continuous corn), and two irrigation regimes where evaluated on Weld silt loam soil study initiated in 2001. At surface foot, the percent gained of SOC when using the ESM calculation scenario was similar to what we observed when SOC was calculated on a concentration basis (19.7%). This indicated that the ESM was more effective in evaluating SOC stock due to the similarity to the changes in SOC concentration compared with the fixed depth scenario. In addition, The ESMmin method appears to be an effective scenario for SOC evaluation from a single sampling event. Over all, we recommend that the fixed depth scenario also be included in future SOC evaluations so that comparisons with historical studies on changes in SOC with management and time can be made.

Technical Abstract: Throughout the years, many studies have evaluated changes in soil organic carbon (SOC) mass on a fixed-depth (FD) basis without considering changes in soil mass caused by changing bulk density ('b). This study evaluates the temporal changes in SOC caused by two factors: (i) changing SOC concentration and (ii) changing equivalent soil mass (ESM) in comparison with FD. In addition, this study evaluates calculating changes in SOC stock over time using a minimum equivalent soil mass (ESMmin) basis from a single sampling event compared with the FD scenario. A tillage [no-tillage (NT) and chisel plow (CP)]-crop rotation (multiple crop and continuous corn), and irrigation (full and delayed)) study was initiated in 2001 on Weld silt loam soil. After seven years, SOC concentration in the 0 - 30 cm depth was 19.7% greater in 2008 compared with 2001. Standardizing the soil mass of 2001 to the ESM of 2008 for each individual treatment showed an average gain in SOC of 5.8 Mg C ha-1 in 2008 compared with 2001. However, the increase in SOC using ESM was twice the SOC gained with the FD calculation, where some treatments lost SOC after seven years of management. Estimating SOC levels using the ESMmin and, thereby, eliminating the confounding effect of soil 'b indicated that SOC stock was influenced by crop species and their interaction with irrigation, but not by tillage practices. Over all, the ESM calculation appears to be more effective in evaluating SOC stock than the FD calculation.