Soil Organic Matter

Definition

Soil organic matter (SOM) is the organic component of soil, consisting of decomposed plant and animal material, microorganisms, and other organic compounds. It plays a crucial role in improving soil structure, enhancing nutrient availability, and supporting a diverse microbial community. This living and dead matter is essential for sustaining the soil food web, fostering healthy ecosystems, and promoting plant growth.

5 Must Know Facts For Your Next Test

1. Soil organic matter typically comprises 3-5% of the total soil weight but has a profound impact on soil health and fertility.
2. It improves water retention in soils, making it easier for plants to access moisture and nutrients, particularly during dry periods.
3. SOM is a primary food source for many soil organisms, contributing to a thriving soil food web that supports ecosystem balance.
4. The decomposition of organic matter by microbes releases nutrients like nitrogen and phosphorus, which are essential for plant growth.
5. Maintaining or increasing soil organic matter is vital for sustainable agriculture, as it enhances soil structure, resilience against erosion, and overall productivity.

Review Questions

• How does soil organic matter influence microbial life in the soil food web?
  • Soil organic matter serves as a vital energy source for various microorganisms in the soil food web. When organic materials decompose, they release nutrients that are crucial for the survival and growth of these microbes. In turn, the activity of these microorganisms helps break down more organic matter, creating a cycle that enriches the soil with nutrients while supporting diverse life forms within the ecosystem.
• Discuss the relationship between soil organic matter and soil structure. How does this relationship affect plant growth?
  • Soil organic matter greatly influences soil structure by promoting the formation of aggregates, which improve aeration and water infiltration. A well-structured soil allows roots to penetrate more easily and access necessary nutrients. This enhanced structure also helps retain moisture, reducing drought stress on plants, ultimately leading to healthier growth and higher crop yields.
• Evaluate the role of soil organic matter in sustainable agricultural practices and its implications for food security.
  • Soil organic matter plays a critical role in sustainable agriculture by enhancing soil fertility, structure, and biodiversity. Practices that focus on maintaining or increasing SOM—like cover cropping, reduced tillage, and composting—can lead to healthier soils that are more resilient to climate extremes. This resilience directly impacts food security by ensuring consistent agricultural productivity and reducing reliance on chemical fertilizers, making it essential for future farming sustainability.

Related terms

Humus: Humus is a dark, organic material formed from the decomposition of plant and animal matter that contributes to soil fertility and structure.

Microbial Biomass: Microbial biomass refers to the total mass of microorganisms in a given volume of soil, playing an important role in nutrient cycling and organic matter decomposition.

Soil Carbon Sequestration: Soil carbon sequestration is the process by which carbon dioxide is captured and stored in soil organic matter, helping to mitigate climate change.