1. Dehydrogenase activity (DHA) is an indicator of soil microbial activity and the biological oxidation of soil organic matter. DHA transfers hydrogen from organic substrates to inorganic acceptors as part of microbial redox processes. 2. Several soil factors influence DHA, including moisture, aeration, organic matter content, pH, temperature, soil profile depth, and fertilizer use. Higher soil moisture, organic matter, and pH generally increase DHA, while lower aeration and deeper soil depths decrease DHA. 3. DHA can be used to measure disruptions to the soil from pesticides and trace elements, as higher enzyme activity indicates lower amounts of contaminants.

1. AGM 301 AGRICULTURAL MICROBIOLOGY
(1+1)
Presented By…
Guhan.C, B.Sc.(Hons).Agri,
JKKMCAS Erode, TN.
201033029.

2. INTRODUCTION
• A dehydrogenase (also called DH or DHase) is
an enzyme belonging to the group of oxidoreductase that
oxidizes a substrate by reducing an electron acceptor.
• Determination of DHA in the soil samples gives information
about biological characteristic of the soil.
• Soil DHA strongly increases under anaerobic conditions.
• Red colors of soil - DHA is higher.
• Light red colors soil - lower DHA.

3. DEHYDROGENASE ACTIVITY IN SOIL
• Dehydrogenases are the important indicator of soil microbial
activity - microbial oxido-reduction processes.
• DHA play a significant role in the biological oxidation of SOM
by transferring hydrogen from organic substrates to inorganic
acceptors.
• Many specific dehydrogenases transfer hydrogen to either
nicotinamide adenine dinucleotide or nicotinamide adenine
dinucleotide phosphate.
• DHA serves as an indicator of the microbiological redox-
systems.
• DHA is considered a good and adequate measure of microbial
oxidative activities in soil.

4. Contd…
• DHA is known to oxidize SOM by transfering protons and
electrons from substrate to acceptors.
• DHA is used to measure any disruption caused by pesticides,
trace elements to the soil.
• Higher enzyme activity - lower the amount of pesticides.

5. SOIL FACTORS INFLUENCE DHA…
1. Soil Moisture.
• Water availability - affects soil enzymatic activities.
• Soils dry - water potential ↑ - enzyme activity ↓.
• Wet soils - increased soil solution soluble OM -
bacterial population ↑.
2. Soil aeration.
• Soil water content ↓ - Oxygen Diffusion Rate (ODR) and redox
potential ↑ - favourable for DHA.

6. 3. Organic Matter Content.
• Soil OM as an indicator of soil quality.
• Its character of nutrient sink and source enhance soil physical
and chemical properties, and also promote biological activity.
• The higher OM - higher microbial biomass - higher enzyme
production.
4. pH.
Enzyme activities tend to increase with soil pH.

7. 5. Temperature.
• Its activity is highest at a temperature close to optimum temp (5 –
30 ̊ C) for mo growth and their development.
• The rate of enzyme catalysis increases with increase in
temperature until the unfavorable temperature, at which enzyme
becomes denaturized and hence its activity reduces.
6. Depth of soil Profile.
• Highest mo abundance in the surface layer of the soil profile
(till to the depth of 30 cm),
• At deepest part of the soil the no.of.microbial cells is limited,
and also DHA level at diminishing trend.

8. 7. Fertilizer.
• Inorganic fertilizers had relatively less effect on soil enzymes
activity than organic fertilizers.
• DHA usually reached higher level in the organic treatments.
8. Heavy metals.
• Heavy metals can reduce enzyme activity by interacting with the
enzyme-substrate complex, denaturing the enzyme protein or
interacting with the protein-active groups.

9. Reference :
E – Ref :
https://www.intechopen.com/books/dehydrogenases/dehydrogenase-
activity-in-the-soil-environment.
Book – Ref :
1. N.S.Subba Rao (1999), “Soil Microbiology” – Science Pub Inc ;
Subsequent Edition.
2. Bagyaraj .D.J, Rangaswami .G (2000), “Agricultural Microbiology” –
PHI Learning Pvt. Ltd. ISBN – 9788120306684, 8120306686.