Tóth T. and B. Szabó. 2003. Method for the quick determination of soil organic 
matter in the field (Hung.). Agrokémia és Talajtan. 52:409-508.

With the use of 60 representative samples, a laboratory comparison was made of 
field methods suitable for the determination of soil organic C content. The 
methods were evaluated by comparing them with the standard Tyurin method. The 
colour of the soil samples, especially the value read from the Munsell Colour  
Chart, exhibited a close correlation (R=0,73**) with the logarithm of the soil 
humus content. This indicates that it would be worth carrying out more detailed 
studies on the correlations between organic C content and soil colour. The field 
Walkley-Black method differs from the laboratory technique only in the quantity 
of reagents applied, so  the organic matter is oxidized using potassium 
bichromate in concentrated sulphuric acid. When the sulphuric acid is added, the 
solution heats up considerably, so it must be cooled before being poured into 
test-tubes for a comparison of the colour of the solutions. As this method is 
dangerous it is not really suitable for field use. Both the absorbance measured
using the field method (R=0,73**) and the order of the samples on the basis of
absorbance (R=0,87**) exhibited a close correlation with the humus content
determined using the Tyurin method. There was a correlation coefficient of
0,78** between the logarithm of the humus content and the basic EDTA
transmittance. It was observed during the investigations that certain soil
components (CaCO3, iron and aluminium oxides) modified the colour of the
solution, thus interfering with organic matter estimation. The newly elaborated
method involves treating the soil with acidic potassium permanganate solution,
followed by the measurement of the carbon dioxide concentration formed over a
period of three minutes, using a portable instrument with an infrared detector.
The inorganic carbonate content of the soil is measured separately with the
addition of sulphuric acid only. The correlation coefficient between the CO2
content recorded with the potassium permanganate method and the Tyurin humus
content was 0,76**, while it was 0,81** for soil samples having less than 20%
carbonate. Further improvement of the new method will be based on modifying the
amount of sulphuric acid and water in such a manner that the concentration of
acid during the determination of carbonates and organic matter should be the
same. The present recovery rates of 12,5% for carbonate and 0,7% for organic
carbon must also be improved in order to decrease the very different effects of
the two carbon sources during the determination in the case of sample
inhomogeneity. The reliability of the methods was tested by analyzing 12 samples
in 4 replications using the coefficient of variation (CV). The smallest CV was
obtained for methods based on the order of soil organic carbon values, followed
by the Walkley-Black, Tyurrin, basic EDTA and potassium permanganate methods.
The final comparison of the methods screened in the 
laboratory will be carried out in the field.