1. Soil Organic Matter Determination SSoil organic matter quantity - Can be expressed as a percentage - Can be expressed as mg.g -1 The wet oxidation of SOM using acid dichromate (K 2 Cr 2 O 7 ) is followed by the potentiometric titration with ferrous ammonium sulfate – Tjurin method SSoil organic matter quality - Can be evaluated by C:N ratio - Can be evaluated by Humic acid and Fulvic acid ratio Measuring of soil extract absorbance

2. SOM Quantity Determination 1.Grind the soil and sieve it through 0.25 mm sieve 2.Weight 0.3 g into 100-150 ml beaker 3.Add 10 ml of K 2 Cr 2 O 7 into the beaker 3.Stir the soil with K 2 Cr 2 O 7 carefully 4.Cover the beaker using the watch glass 5.Insert the beaker into the oven (125°C) for 45 min. 6.Wash the beaker side and watch glass using distilled water 7.Titration with (NH 4 ) 2 Fe(SO 4 ) 2

3. Tjurin method Equation 2 K 2 Cr 2 O 7 + 8 H 2 SO 4 → K 2 SO 4 + 2 Cr 2 (SO 4 ) 3 + 8 H 2 O + 3 O 2 3 O 2 + 3 C → 3 CO 2 K 2 Cr 2 O 7 + 7 H 2 SO 4 + 6 Fe(NH 4 ) 2 (SO 4 ) 2 → K 2 SO 4 + Cr 2 (SO 4 ) 3 + 3 Fe 2 (SO 4 ) 3 + 6 (NH 4 ) 2 SO 4 + 7 H 2 O Acid dichromate Mohr salt

4. Calculation Factor of Mohr salt Cox Humus content...

5. Evaluation of Cox/Humus Content Cox (%)Humus (%)Evaluation < 0.6< 1.0very low 0.6 – 1.11.0 – 2.0low 1.1 – 1.72.0 – 3.0medium 1.7 – 2.93.0 – 5.0high > 2.9> 5.0very high

6. SOM Quality determination Spectrophotometric method for determining the humus quality in VIS  Soil extract preparation : 2g of soil + 20ml 0.05M Na 4 P 2 O 7 (buffered to pH 12)  Methodology: - Shake the soil suspension for 1 hour - Centrifuge the soil suspension by 11 000 rpm. for 2 min. - Move the transparent soil extract to the test-tube - If it’s necessary, dilute the soil extract by Na 4 P 2 O 7 (the final extract has to have colour like a weak tea, or the light beer)  Measure the soil extract absorbance by the wavelength of 400 and 600 nm

7. SOM Quality Spectrophotometric method for determining the humus quality in UV-VIS  Principle: more polymerized substances (superior humus substances, especially) absorb long-wave radiation more than less polymerized substances (FA) I0I0 I L  Transmission T=I / I 0 (0-1;0-100%)  Absorption B=1-T (0-1;0-100%)  Absorbance A=log1/T=logI 0 /I Lambert – Beer law T=10 - ε cL c...concentration, L... thickness, ε... coefficient of absorption =εcL !!! A<1 !!!

8. Humic Substances Extraction Soil Soil without bitumens bitumens ® HU + mineral partHA + FA +HY ® HUmineral part ®HA + HYFA ®FA ® HAHAHY ® Organic solvent (Benzene) Alkaline solution (NaOH, Na 4 P 2 O 7 ); pH 12 HFAcid solution (HCl); pH 1-2 Ethanol

9. SOM Quality Humic substances Humin Humic Acids Fulvic Acids - Decrease of colour intensity - Decrease of polymerization and humification - Decrease of C content - Increase of acidity - Increase of O content

10. SOM Quality Results evaluation  Absorbance curve: SOM of higher quality SOM of lower quality Absorbance wavelength

11. Results evaluation  Absorbance curve: A X =f(λ)  Optical parameter of humus quality Q 4/6 : Q 4/6 =A 400 /A 600 - the lower the Q 4/6 value the higher the SOM quality - The limit value for quality and poor-quality SOM is 3.6  HA:FA according to Pospíšil: HA:FA=17.2(Q 4/6 -2.19 ) - empirical formula between the Q 4/6 value and HA:FA ratio - The higher value of this ratio the higher SOM quality 1=17.2(3.6 -2.19 ) SOM Quality