Why not use chromate or combustion methods?

Even extraction by conc strong base will leave some behind

The most common procedure involved is the reduction of potassium dichromate by organic carbon compounds and subsequent determination of the unreduced dichromate by oxidation-reduction titration with ferrous ammonium sulfate (FAO, 1974), while the actual measurement is the oxidizable organic carbon, we prefer to report as oxidizable organic carbon, or multiplied by 1.334 as total organic carbon (assuming that organic matter contains 58% organic carbon.

Dear Rotem Cahanovitc,

Dry combustion at high temperatures in a furnace with the collection and detection of evolved CO2 (Tiessen and Moir, 1993) is the the most accurate method to determine TOC in soil.

However, If you do not have this facility, you can use the method mentioned by J. C. Tarafdar, as alternative.

for more information, refer the link below

http://bcodata.whoi.edu/LaurentianGreatLakes_Chemistry/bs116.pdf

Piyal Aravinna