A comparison of three methods of organic carbon determination in some New Zealand soils
Article first published online: 28 JUL 2006
Journal of Soil Science
Volume 42, Issue 2, pages 251–257, June 1991
How to Cite
GREWAL, K. S., BUCHAN, G. D. and SHERLOCK, R. R. (1991), A comparison of three methods of organic carbon determination in some New Zealand soils. Journal of Soil Science, 42: 251–257. doi: 10.1111/j.1365-2389.1991.tb00406.x
- Issue published online: 28 JUL 2006
- Article first published online: 28 JUL 2006
- (Received 5 June 1990; accepted 14 January 1991)
A dry combustion (Dumas) reference method for measuring total organic C (T), is compared with two other methods: the wet acidified dichromate oxidation, Walkley-Black procedure (an estimator of organic C) and loss on ignition (L) (an estimator of organic matter) for 40 samples from various depths from five New Zealand mineral soils, spanning a range of textures and cultivation treatments. Regression analyses reveal the following: (1) an excellent linear relation exists for all samples between Walkley-Black procedure and reference method results, with a mean conversion factor 1.25, which compares with the original value 1.32 recommended by Walkley & Black (1934).
(2) L and T are less well-related by an equation of the form L=a+bT. In contrast to the traditional assumption that b≃ 1.72 and a≃ 0, a strong ‘intercept effect’ (a > 0) is revealed, reflecting removal on ignition of non-organic soil constituents. An improved regression of the form L=a+bT+cC, where C= percentage of clay, obtained by inclusion of the clay as an independent variable, points to the role of clay in releasing these constituents, chiefly adsorbed water.