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Investigation of Soil Organic Carbon Recovery by the Walkley-Black Method Under Diverse Vegetation Systems

Bahadori, Mohammad1; Tofighi, Hasan PhD2

doi: 10.1097/SS.0000000000000201
Technical Article

ABSTRACT The Walkley-Black (WB) method has been widely used during the past 50 years because of its simplicity and rapidity. The main problem with this method is its incomplete oxidation of soil organic carbon (OC) and inconstancy in efficiency of oxidation in different soils. A practical way to improve the accuracy of this method is by applying a correction factor. However, correction factors can be affected by environmental conditions, vegetation, soil characteristics, and systems of cultivation. The objectives of this study were to evaluate the efficiency of the WB method in soils under four diverse vegetation systems and to introduce appropriate correction factors for each vegetation system. In this study, 94 composite soil samples were collected from soils under pastures, a forest, and from rice and annual crop fields. In addition, 16 samples from saline soils were analyzed to find the possible effect of salinity on the efficiency of the WB method. The OC contents of the samples were measured by the WB method and by a total carbon analyzer, and the obtained data were statistically analyzed with the Duncan method. The results demonstrated that there is a significant difference between soil OC recovery by the WB method under diverse vegetation systems and also in soils with different contents of OC and salinity, with correction factors ranging from 1.21 (annual crops in soils with OC >1%) to 2.26 (pastures in soils with OC <1%). Differences in the efficiency of the WB method were attributed to changes in the residue fragmentation and quality as a result of the cultivation or vegetation system, as well as the presence of chloride ions in saline soils.

1Australian Rivers Institute, Griffith University, Brisbane, Australia.

2Department of Soil Science, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

Address for correspondence: Mr Mohammad Bahadori, Australian Rivers Institute, Griffith University, 170 Kessels Road, Nathan, Brisbane, QLD 4111, Australia. E-mail:

Received June 1, 2016.

Accepted for publication April 19, 2017.

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