1. Oxygen (O2): Oxygen is essential for root respiration and microbial activity in the soil. It is consumed by microorganisms during the decomposition of organic matter and is also used by plant roots for respiration.

2. Carbon dioxide (CO2): Carbon dioxide is produced as a byproduct of microbial respiration and root respiration. It is an important greenhouse gas and plays a crucial role in regulating the soil's pH and nutrient availability.

3. Methane (CH4): Methane is a potent greenhouse gas produced under anaerobic conditions in waterlogged soils. It is primarily produced by methanogenic bacteria during the decomposition of organic matter in the absence of oxygen.

4. Nitrogen (N2): Nitrogen is the most abundant gas in the atmosphere and is also present in soil. However, it is mostly unavailable to plants in its gaseous form. Nitrogen-fixing bacteria convert atmospheric nitrogen into forms that can be utilized by plants.

5. Nitrous oxide (N2O): Nitrous oxide is a potent greenhouse gas and ozone-depleting substance. It is produced through microbial processes, including nitrification and denitrification, and can be influenced by factors such as nitrogen fertilization, soil moisture, and temperature.

6. Hydrogen sulfide (H2S): Hydrogen sulfide is a toxic gas produced under anaerobic conditions in certain soils, particularly those with high organic matter content and low oxygen levels. It is associated with sulfate-reducing bacteria and can have adverse effects on plant growth.

The composition of soil gases can vary depending on factors such as soil type, moisture content, temperature, microbial activity, and plant root activity.