Subscribe Now Subscribe Today
Research Article
 

Colorimetric Determination of Organic Carbon in Soils by Dichromate Digestion in a Microwave Oven



F. Azam and M.H. Sajjad
 
Facebook Twitter Digg Reddit Linkedin StumbleUpon E-mail
ABSTRACT

External heating of soil samples following addition of dichromate is a commonly used method for the determination of organic carbon (C). We have successfully standardized microwave oven as a source of external heating for reliable and quick determination of organic C in soil samples by colorimetric method. Ten soils varying in C content were collected from agricultural fields differing in physico-chemical and other characteristics. The method involves: I) addition of 8 mL of conc. H2SO4 and 5 mL of 2N K2Cr2O7 solution to soil samples containing ca 5 mg C and placed in 100 mL glass beakers, ii) heating the treated samples in a microwave oven with rotating plate, iii) dilution of the contents of the beaker to 50 mL with distilled water, iv) determination of optical density of the samples at 590 nm, v) calculations for C content against a glucose standard (5 mg C mL-1 solution; 1.25 g glucose 100-1 mL) treated like the samples. The newly developed method gives values of C lower than those obtained with the conventional colorimetric method and Walkley-Black method. However, almost perfect correlations existed between the values obtained by the three methods. Regression equations thus developed can conveniently be used for the accurate measurement of organic C in soil samples. Time of heating in microwave oven that varied from 45 to 120 sec did not have a significant bearing on the amount of C determined. Hence, heating for 60 sec can conveniently be adopted for routine analysis. The proposed method is not only quick but highly economical in terms of energy used in heating the samples.

Services
Related Articles in ASCI
Similar Articles in this Journal
Search in Google Scholar
View Citation
Report Citation

 
  How to cite this article:

F. Azam and M.H. Sajjad , 2005. Colorimetric Determination of Organic Carbon in Soils by Dichromate Digestion in a Microwave Oven. Pakistan Journal of Biological Sciences, 8: 596-598.

DOI: 10.3923/pjbs.2005.596.598

URL: https://scialert.net/abstract/?doi=pjbs.2005.596.598

REFERENCES
1:  Nelson, D.W. and L.E. Sommers, 1996. Total Carbon, organic carbon and organic Matter. In: Methods of Soil Analysis, Part 3: Chemical Methods, Sparks, D.L., American Society of Agronomy/Soil Science Society of America, Madison, WI., USA., ISBN-13: 978-0891188254, pp: 961-1010.

2:  Walkley, A. and I.A. Black, 1934. An examination of the degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Sci., 37: 29-38.
CrossRef  |  Direct Link  |  

3:  Walkley, A., 1947. A critical examination of a rapid method for determining organic carbon in soils-effect of variations in digestion conditions and of inorganic soil constituents. Soil Sci., 63: 251-264.
CrossRef  |  Direct Link  |  

4:  Carolan, R., 1948. Modification of Graham`s method for determining soil organic matter by colorimetric analysis. Soil Sci., 66: 241-248.
Direct Link  |  

5:  Rhiem, H. and B. Ulrich, 1954. Quantitative colorimetrisch bestimung der organischen substanz im boden. Landwirtsch. Forsch., 6: 173-176.

6:  Nelson, D.W. and L.E. Sommers, 1975. A rapid and accurate method for estimating organic carbon in soil. Proc. Indiana Acad. Sci., 84: 456-462.

©  2021 Science Alert. All Rights Reserved