African Journal of
Agricultural Research

  • Abbreviation: Afr. J. Agric. Res.
  • Language: English
  • ISSN: 1991-637X
  • DOI: 10.5897/AJAR
  • Start Year: 2006
  • Published Articles: 6638

Full Length Research Paper

Loss on ignition: Measuring soil organic carbon in soils of the Sahel, West Africa

H. Konare1, R. S. Yost2*, M. Doumbia1, G. W. McCarty3, A. Jarju4 and R. Kablan2
1Labo SEP, Institut d’Economie Rurale, BP 262 Bamako-Mali. 2University of Hawai`i, 3190 Maile Way, St. John 102, Honolulu, Hawaii 96822, USA. 3USDA-ARS, Hydrology and Remote Sensing Laboratory, Beltsville, Maryland, USA. 4National Agricultural Research Institute, Gambia.
Email: [email protected]

  •  Accepted: 27 September 2010
  •  Published: 18 November 2010

Abstract

Traditional methods of measuring soil organic carbon (SOC) are not adequate for accurate evaluation of C sequestration nor to meet environmental safety requirements. Methods that permit accurate assessment of SOC, which are environmentally healthy, and yet feasible for use in developing countries are needed. Initial and ignition temperatures were adjusted so that loss on ignition (LOI) measures of SOC matched measurements by combustion methods. A comparison of combustion, LOI, and Walkley-Black methods was carried out with soils of Mali, West Africa, ranging from 2 - 25 g kg-1 SOC. The LOI method, when using initial (preparation) temperatures of 105°C and ignition temperatures of 350°C, related closely with combustion measures (Adj. R2 of 0.89). The SOC measurements by combustion, however, differed from those of Walkley-Black procedure. The LOI calibration equation was %C (combustion) = 0.03 + 0.36 x %weight loss by LOI, adj. R2=0.89. The Mali calibration of LOI with combustion SOC was tested on soils of Gambia, however, a systematic over-prediction suggested that re-calibration may be needed to ensure LOI method accuracy with soils different from the calibration set. This need for re-calibration is similar to the Type 2 error, where the sample belongs to a different calibration set.

 

Key words: Loss on ignition, Sahel, Mali, Africa, carbon sequestration, combustion, Walkley and Black.