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Chapter 8: Problem 1

Distinguish between soil organic matter, humus, and soil biomass.

Short Answer

Expert verified
Soil organic matter encompasses all organic components, humus is the stable form of SOM, and soil biomass consists of living organisms in the soil.

Step by step solution

01

Identify Soil Organic Matter

Soil Organic Matter (SOM) consists of plant and animal residues in various stages of decomposition, living organisms, and substances synthesized by soil organisms. It includes all organic components found within the soil.
02

Discuss Humus

Humus refers to the stable fraction of soil organic matter that remains after the susceptible and labile organic matter has decomposed. It is the portion of SOM that contributes to moisture retention, colloidal stability, and nutrient availability in the soil.
03

Explain Soil Biomass

Soil biomass is made up of the living component of organic matter present in the soil, including microorganisms like bacteria, fungi, and larger soil fauna. These organisms play a critical role in organic matter decomposition and nutrient cycling.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Soil Organic Matter
Soil Organic Matter (SOM) is an essential component of soil that plays a crucial role in its health and fertility. It is a complex mix of materials that includes both living and non-living entities.
  • Plant Residues: This refers to bits of plants like leaves, stems, and roots that have been added to the soil. These residues are in various stages of decomposition.
  • Animal Residues: These are remnants of animals, such as decomposed carcasses or waste products.
  • Decomposed Matter: As these plant and animal materials break down, they form part of the organic matter.
  • Living Organisms: The living portion includes organisms that reside in the soil, such as bacteria, fungi, and insects.
  • Synthesized Substances: These are compounds released by soil organisms during decomposition.
Understanding SOM is crucial because it influences soil structure, aeration, water retention, and nutrient supply. It is foundational for sustainable agriculture and ecological balance.
Humus
Humus is an important and stable component of Soil Organic Matter. While SOM includes all organic material, humus specifically refers to the well-decomposed part that has reached a condition where it will change little in the presence of soil organisms. Humus is dark, spongy, and amorphous, contributing several benefits to soil:
  • Moisture Retention: Its sponge-like structure helps in holding water, which is vital for plant growth, especially in dry periods.
  • Colloidal Stability: It improves soil texture and structure, making it more cohesive. This helps in preventing erosion and compaction.
  • Nutrient Availability: Humus can store and provide essential nutrients to plants in a slow-release manner, aiding in their growth.
Unlike the more labile (easily decomposed) organic materials, humus changes slowly, slowly releasing nutrients over time and helping maintain soil health.
Soil Biomass
Soil Biomass refers to the living component of the organic matter in the soil. It includes microorganisms (such as bacteria and fungi) and larger soil animals (such as earthworms, insects, and small mammals). These living organisms are vital for the following reasons:
  • Decomposition: Soil organisms break down complex organic materials into simpler substances, facilitating nutrient cycling.
  • Nutrient Cycling: They help release nutrients back into the soil, making them available for plant uptake.
  • Soil Structure: Their activities affect soil aeration and structure, improving the movement of air and water through the soil.
Healthy soil biomass is a sign of a biologically active soil, which is indispensable for the ecosystem functioning and productive agriculture. It forms the backbone of soil fertility and plays a significant role in maintaining the ecological balance.

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Most popular questions from this chapter

Why are organic phosphate compounds in soils important?

Describe the role of water in SOM structure composition in soils. Hint: Consider hydrophobic and hydrophilic interactions.

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