Weathering and Soil Science Notes

Weathering and Soil Science

Introduction

  • "A Nation That Destroys its Soil, Destroys Itself" - FDR, in response to the Dust Bowl during the 1930s.
  • The quote emphasizes that a nation's ability to feed itself depends on its soil.
  • This section covers soil formation, essential components of soil fertility, soil problems, and sustainable solutions for farmers.
  • Understanding soil is foundational to understanding agriculture because you cannot grow food without soil.

Soil Formation: Rock Cycle, Weathering, and Decomposition

  • Soil (aka dirt) is a combination of minerals released from rocks and organic material (mostly carbon) from the biological decomposition of living organisms and their waste products.
  • Soil development occurs before plants can establish and ecosystems diversify.
  • The mineral component of soil depends on the parent rock.
  • Example: A rock with a lot of Iron (Fe) will produce soil rich in Iron (Fe).
  • Soils have different mineral combinations, influencing crop selection (e.g., spinach on iron-rich soils, bananas on potassium-rich soils).
  • The geological process of weathering releases minerals from rock to soil.
Geological Mechanisms of Weathering
  • Physical Weathering (Most Common)
    • Frost/thaw: Water freezes and expands in cracks.
    • Wind: Blowing sand across the surface of rocks acts like sandpaper.
    • Wave action or rivers breaking rocks.
    • River flows carry sediments, acting like sandpaper (smooth river rocks).
  • Chemical Weathering
    • Rainwater is slightly Acidic (CO2 + H2O >>> Carbonic Acid) weathers rocks.
      • Anthropogenic acid rain accelerates this process.
    • Oxygen is corrosive (Iron rusting).
  • Biological Weathering
    • Tree roots growing into cracks in rocks.
    • Marine organisms burrowing.
  • Weathering breaks down rock, and erosion carries mineral-rich sediments away.
    • Erosion is the process by which mineral-rich sediments are carried away from the landscape by wind and water and deposited in sediments.
  • Organic material is added to the sediment over time.
  • Decomposers (earthworms, pill bugs, fungus, and decomposing bacteria) break down organic material.
    • This releases carbon, nitrogen, and phosphates into sediments, forming fertile soil.
  • Soil formation can take thousands of years; therefore, fertile arable soils are considered a non-renewable resource.
  • The rate of soil formation varies depending on geography.
    • Soils develop slowly in arctic regions and rapidly in tropical latitudes.
Check for Understanding:
  1. Difference between broken rock (sand) and fertile soil:
    • Broken rock is just mineral particles.
    • Fertile soil contains minerals and decomposed organic matter, supporting plant growth.
  2. Different mineral concentrations:
    • Soils inherit mineral composition from parent rocks.
    • Farmers choose crops based on soil mineral content.
  3. Geological mechanisms of mineral release:
    • Weathering breaks rocks into smaller pieces.
    • Erosion transports these pieces.
  4. Organic component addition:
    • Decomposition of organic material (leaves, dead organisms) by decomposers.
  5. Abiotic factors in tropical latitudes:
    • High temperatures, humidity, and rainfall promote rapid weathering and decomposition.
  6. Role of earthworms and other soil organisms:
    • Aerate the soil, decompose organic material, and recycle nutrients.

Properties of Soil & Fertility: Physical, Chemical and Biological Components of Soil

  • Lands that contain soils fertile enough to support crops are called arable lands. What makes the soil on these arable lands fertile enough to support crops is a combination of the physical, chemical and biological components of the