Soil Fertility and Components

Soil Fertility

• Rich soils are NOT always considered fertile.

Soil Texture and Permeability

• Relationship between grain size and permeability of soil should be described.
• Soil texture should be examined using Figure 25 (page 244).

Essential Components of Soil Fertility

• Loss of essential soil components due to poor farming practices or erosion leads to loss of ability to support crops.
• Farmers will no longer be able to grow food.
• Understanding how each soil component relates to a plant's ability to survive is important.

Major Soil Properties

Physical Soil Properties (Abiotic Factors)

• Soil Texture/Grain Size:
  • Sand: Largest particles.
  • Silt: Medium particles.
  • Clay: Small particles.
• Texture of soil determines its permeability (ability to hold water).

Chemical Soil Properties (Abiotic Factors)

• Minerals from Parent Rock.
• Soil Air:
  • Oxygen ($O_2$)
  • Nitrogen ($N_2$)
• Soil Water & Mineral Component & Plant Nutrients
  • Nitrates ($NO_3$)
  • Phosphates ($PO_4$)
• Minerals from parent rock and plant nutrients (nitrates) are dissolved in soil water and absorbed by plant roots.
• Soil oxygen is needed for metabolism of ALL soil organisms.
• Nitrogen is needed for Nitrogen-fixing bacteria that convert $N<em>2$ to $NO</em>3$.

Biological Soil Properties (Biotic Factors)

• Humus layer
• Decomposers (Earthworms)
• Decomposing Bacteria and Fungus.
• Soil organisms take in organic material from the Humus layer and decompose it back into the soil.
• This process returns nutrients that plants need to survive.

From Sand to Fertile Soil: A Hypothetical Example

• Consider a glass jar filled with sand where growing tomatoes is attempted, but fails due to lack of essential soil components.

Addressing the Shortcomings of Sand

• Sand contains inorganic mineral nutrients needed for crop growth.
• Sand is derived from parent rock, providing the mineral component.

The Problem with Sand: Grain Size and Water Retention

• Grain size of sand is too large.
• Water added to sand percolates (drains) through, preventing water retention for plant use.
• Plants don't grow in beach sand because sand cannot hold water.

Creating Loam

• Add equal parts silt and clay to sand to produce loam.
• Loam: A mixture of sand, silt, and clay.
  • Combination of soil particles create air spaces and trap water.
• Figure 25.8 illustrates the different textures of soil types.
  • Understanding how to read the figure to determine different soil types is important.

Air and Water Retention in Loam

• Loam contains rock particles small enough to trap air and water, and large enough to create space for storage.
• Soil air contains oxygen for plant roots and soil organisms to metabolize sugar.
• Soil air contains atmospheric nitrogen gas ($N_2$) for conversion into nitrates by nitrogen fixers.
• Soil water is crucial for survival of all living things in the soil.
• Minerals, nitrates, and phosphates must be dissolved in water for absorption by plant roots.

Adding the Biological/Organic Component

• In nature, biological components are added via ecological succession; this process needs to be sped up artificially.
• Add organic material (leaf material, animal waste etc.) to the top of the soil.
  • Organic Layer/Humus Layer - Also known as compost.
  • Humus layer serves as food for soil organisms.

The Role of Earthworms and Decomposers

• Earthworms tunnel to the surface and consume the humus layer.
• Earthworm poop is nutrient-rich waste added to the soil.
• Decomposing bacteria feed on this waste, returning minerals and nutrients to the soil via decomposition.

Achieving Soil Fertility

• At this point, the soil is considered fertile.
• Tomatoes planted in this soil will grow.
• Natural soil fertility is a process that takes time.