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). This study evaluates 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, 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 ρb 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.
Cite this paper
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