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Soil Carbon Changes Influenced by Soil Management and Calculation Method

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 (ρb). In this paper, the authors evaluated the temporal changes in SOC caused by two factors: 1) changing SOC concentration; and 2) changing equivalent soil mass (ESM) in comparison with FD. In addition, they also evaluated 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 ρb indicated that SOC stock was influenced by crop species and their interaction with irrigation, but not by tillage practices.

In conclusion, the findings of the study indicate that the ESM was more effective in evaluating SOC stock due to the similarity to the temporal changes in SOC concentration compared with the FD scenario. The ESMmin method appeared to be an effective scenario for SOC evaluation from a single sampling event. Therefore, it’s advisable to sample several centimeters below the chosen depth of interest to allow for SOC evaluation with different scenarios.

Article by Maysoon M. Mikha, et al, from USA.

Full access: http://mrw.so/21qjlg

Image by FAO of the UN, from Flickr-cc.

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