Soil organic matter

Definition

Soil organic matter refers to the complex mixture of decomposed plant and animal materials, microorganisms, and organic compounds found in soil. It plays a crucial role in soil health and fertility, serving as a reservoir of nutrients, improving soil structure, and enhancing water retention. Understanding soil organic matter is essential for comprehending its vital functions in the carbon cycle and the involvement of microorganisms in these processes.

5 Must Know Facts For Your Next Test

1. Soil organic matter typically constitutes 2-6% of the total soil weight but has a disproportionate impact on soil health and fertility.
2. Microorganisms are essential for breaking down organic matter into simpler forms that can be used by plants, thus linking soil organic matter to nutrient cycling.
3. The decomposition of soil organic matter releases carbon dioxide back into the atmosphere, playing a significant role in the carbon cycle.
4. Higher levels of soil organic matter improve soil structure, leading to better aeration and water infiltration, which benefits plant growth.
5. Management practices that enhance soil organic matter, such as cover cropping and reduced tillage, are critical for sustainable agriculture and carbon sequestration efforts.

Review Questions

• How does soil organic matter contribute to nutrient cycling in ecosystems?
  • Soil organic matter serves as a reservoir for essential nutrients, providing a source of nitrogen, phosphorus, and sulfur as it decomposes. Microorganisms break down this organic material into simpler compounds that plants can absorb. This process not only recycles nutrients but also enhances soil fertility, supporting plant growth and maintaining ecosystem productivity.
• Evaluate the impact of soil organic matter on soil structure and water retention.
  • Soil organic matter significantly improves soil structure by promoting the formation of aggregates, which helps create pore spaces for air and water movement. These aggregates increase water retention capacity by allowing soils to hold moisture more effectively. As a result, soils with higher levels of organic matter are more resilient during droughts and can support healthier plant growth due to improved access to water.
• Discuss how changes in land management practices can influence soil organic matter levels and their subsequent effects on the carbon cycle.
  • Land management practices such as deforestation, intensive agriculture, and overgrazing can lead to a decrease in soil organic matter levels due to increased erosion and reduced input of organic materials. Conversely, practices like cover cropping, reduced tillage, and agroforestry can enhance soil organic matter accumulation. These changes directly affect the carbon cycle by influencing carbon sequestration rates; improved management practices can enhance soil's ability to store carbon, thereby mitigating climate change impacts while promoting healthier ecosystems.

Related terms

humus:

Humus is the dark, organic component of soil formed from the decomposition of plant and animal materials, contributing to soil fertility and structure.

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

carbon sequestration:

Carbon sequestration is the process by which carbon dioxide is captured and stored in soils or vegetation, helping to mitigate climate change.