Soil Carbon Changes Influenced by Soil Management and Calculation Method

Maysoon M Mikha,Joseph G Benjamin,David C Nielsen,Ardell D Halvorson

doi:10.4236/ojss.2013.32014

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 (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.

Highlights

Numerous studies [1,2,3,4,5,6,7,8] have assessed management practice-induced changes in Soil organic C (SOC) due to anthropogenic and environmental effects
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 fixed depth basis (FD)
The SOC estimation depends on how one calculates changes in soil mass associated with different sampling periods or management practices

Summary

Introduction

Numerous studies [1,2,3,4,5,6,7,8] have assessed management practice-induced changes in SOC due to anthropogenic and environmental effects. Researchers have argued that changes in soil ρb and its effect on unequal soil mass associated with the fixed depth have a confounding effect on SOC mass estimation when comparing changes in SOC associated with different management practices [13,14,15,16,17]. With an acknowledgment that SOC storage depends on soil mass and soil ρb, recent research estimated SOC and other soil nutrients based on their concentration, soil thickness, and soil ρb [13,14,15,16,17,18]. Researchers have suggested alternative methods to calculate SOC and other soil nutrients to account for the changes in soil volume under different management practices [13,14,16]

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