Soil organic matter (SOM) is a good indicator of soil quality and degradation.
SOM is a crucial component of soil health, influencing a wide range of physical, chemical, and biological properties. Its presence signals a healthy and functioning soil ecosystem, while its decline often indicates degradation and reduced productivity. Several factors contribute to SOM's role as a reliable indicator:
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Soil Quality: SOM directly impacts several indicators of soil quality. Higher SOM levels typically correlate with:
- Improved soil structure: SOM binds soil particles together, creating stable aggregates that enhance water infiltration, aeration, and root growth.
- Increased water-holding capacity: SOM acts like a sponge, retaining water that plants can access during dry periods.
- Enhanced nutrient availability: SOM serves as a reservoir of essential plant nutrients, such as nitrogen, phosphorus, and sulfur. It also improves the soil's cation exchange capacity (CEC), which is its ability to hold onto positively charged nutrients.
- Increased biological activity: SOM provides food and energy for a diverse community of soil organisms, including bacteria, fungi, and earthworms. These organisms play crucial roles in nutrient cycling, decomposition, and disease suppression.
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Soil Degradation: Conversely, declining SOM levels are often a sign of soil degradation, which can occur due to:
- Erosion: Loss of topsoil due to wind or water erosion directly reduces SOM content.
- Intensive agriculture: Continuous cultivation, especially without proper soil management practices, can deplete SOM over time. This is because intensive farming often removes crop residues and disrupts soil structure, leading to faster decomposition rates.
- Deforestation: Removing forests and other natural vegetation exposes the soil to erosion and reduces the input of organic matter.
- Overgrazing: Excessive grazing can compact the soil, reduce vegetation cover, and increase erosion, all of which contribute to SOM loss.
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Direct Relationship to Soil Functions: SOM is critical for maintaining essential soil functions, including:
- Carbon sequestration: Soil acts as a major carbon sink, and SOM is the primary storage form of carbon in soil. Increasing SOM can help mitigate climate change by removing carbon dioxide from the atmosphere.
- Nutrient cycling: SOM is involved in the cycling of essential plant nutrients, ensuring their availability for plant uptake.
- Water regulation: SOM improves soil structure and water-holding capacity, which helps to regulate water flow and reduce the risk of flooding and drought.
- Pollution mitigation: SOM can bind pollutants, reducing their mobility and bioavailability, and thus, decreasing their harmful effects on the environment.
In summary, soil organic matter's sensitivity to management practices and its direct influence on soil functions make it a valuable indicator of overall soil health and a key parameter for assessing soil degradation.
