Soil Composition and Human Impact on Soil Characteristics

Soils: Water, Air, and Human Impacts

Water and Air in Soils

  • Water and air each make up approximately 25% of soils.
  • The proportion of water and air in brown earth soils is influenced by several factors:
    • Texture
    • Climate
    • Humus content
    • Relief
  • These components facilitate several soil forming processes, such as leaching.
Irish Climate and Brown Earth Soils
  • The water content in Ireland's brown earth soils is heavily affected by climate.
  • East Ireland: Experiences a rain shadow effect leading to 700 mm of rainfall per year, conducive for mineral leaching toward plant roots.
    • Loamy Texture: Ensures adequate water storage without waterlogging, allowing minerals to dissolve for plant uptake.
    • Sufficient Drainage: Crucial for oxygenation of the soil, supporting microorganisms in decomposing organic materials into humus.
  • West Ireland: Characterized by mountainous relief leading to increased rainfall levels, reaching up to 2000 mm.
    • This results in greater leaching and podzolization processes:
      • Leaching and Podzolization: Loss of minerals except quartz, leading to hardpan formation in the B horizon.
      • Accumulation of iron and aluminum can create impermeable hardpans.
      • Example: Podzolic brown earth soils in regions like Galway.
    • Water Logging: Impedes decomposition, possibly forming peat soils, as seen in regions like County Mayo.
Temperature Effects on Soil Development
  • Air temperatures impact the development of brown earth soils.
  • In upland areas (e.g., Wicklow Mountains):
    • Cooler temperatures result in reduced microbial activity.
    • Less decomposition of organic material leads to lower humus levels and decreased soil fertility.

Human Impacts on Soil Characteristics

  • Major soil characteristics:
    • Organic matter
    • Mineral matter
    • Water content
    • Soil pH
    • Soil texture
    • Soil color
  • Overgrazing: Defined as grazing by livestock exceeding the land's carrying capacity.
    • Effects of Overgrazing:
    • Removal of young trees and shrubs exacerbates soil instability.
    • Soil structure weakens without root support, leading to:
      • Reduction in plant litter
      • Decrease in humus and fertility
    • Increased exposure to direct sunlight leads to quicker soil drying.
    • Trampling by livestock causes soil compaction, hindering water infiltration.
      • Results in surface runoff, reduced soil moisture, and fertility loss.
    • Erosion of dry, loose topsoil over time can lead to significant depth reduction.

Desertification

  • Definition: The formation of aridsols, which are sandy, water-unretentive soils leading to vegetation loss and low fertility.
  • Driving Factors of Desertification:
    • Soil erosion caused by human activities including deforestation and overgrazing.
    • Increased temperatures due to climate change raise CO2 levels.
    • Increased evaporation rates and reduced rainfall contribute to vegetation die-off.
    • Loss of vital roots and plant litter reduces organic matter, exposing soils to erosion.
    • Deforestation: Adds strain due to rising demand for wood and fuel.
    • Trees removed mean loss of protective cover and root strength.
    • Nutrient-rich leaf litter that decomposes for humus is absent, leading to poor water storage and nutrient deficiency in soils.
    • This culminates in the formation of infertile aridsols.

Summary

  • Brown earth soils are significantly impacted by environmental conditions such as water, air, and temperature, and human activities such as overgrazing and deforestation. The resultant changes can lead to severe consequences like desertification, posing threats to soil health and agricultural productivity.