Soil Study Notes

Harvesting Impact on Soil

  • Mechanical Harvesting Effects:
    • Bulk Density (B.D.) measurements from various harvesting methods:
      • No mechanical harvest:
      • Number of fields: 24, B.D.: 1.49 g/cc
      • 1 mechanical harvest:
      • Number of fields: 14, B.D.: 1.50 g/cc
      • 2 mechanical harvests:
      • Number of fields: 17, B.D.: 1.52 g/cc
      • 3+ mechanical harvests:
      • Number of fields: 34, B.D.: 1.60 g/cc
    • Yield suppression noted with increasing B.D., affecting root penetration.

Soil Moisture

  • Importance of Water in Soil:
    • Vital for plant and microorganism life.
    • Different soils have varying water retention capacities affecting:
      • Plant health (too little results in wilting, too much results in oxygen deprivation).
    • Key roles of water include:
      • Promoting plant growth and nutrient availability
      • Influencing soil erosion and structure (creates horizons).
Water Cycle Overview
  • Hydrology studies the water cycle:
    • Snow accumulation, precipitation, percolation, transpiration etc.
    • Water moves through various stages: snowmelt, evaporation, groundwater discharge, etc.
Forces Holding Water in Soil
  • Water retention driven by:
    • Adhesion: Attraction between water molecules and soil particles
    • Cohesion: Attraction among water molecules.
Soil Moisture Constants
  • Field Capacity: Water retained after saturation, available for plant use.
  • Moisture Equivalent: Water retention against centrifugal force.
  • Permanent Wilting Percentage: Water remaining when plants wilt (1-15% range).
  • Hygroscopic Coefficient: Bound water not accessible to plants.
Biological and Physical Classification of Soil Water
  • Free Water: Excess water not held at field capacity, removed via drainage.
  • Capillary Water: Held in soil pores between field capacity and hygroscopic coefficients, essential for plant use.
  • Hygroscopic Water: Thin film around particles, not available to plants.

Water's Role in Plant Growth

  • Plants require significant water content (approx. 80% of green weight).
  • Osmosis: Water absorption through roots driven by concentration gradients.
    • Mineral nutrients are carried along with water uptake.
  • Crop Water Requirement:
    • Water loss through evaporation and transpiration noted as evapotranspiration.
    • Example: Water utilized for producing 1 kg of dry matter varies across crops (e.g., wheat: 452.7 kg water per kg dry matter).

Physical and Biological Properties of Soil Water

  • K-Types of Water:
    1. Free/Drainage: excess water, easy leaching.
    2. Capillary: available for plants, essential nutrient transporter.
    3. Hygroscopic: held tightly, not available.
  • Biologically Active:
    • Water availability tightly linked to soil structure and health impacting nutrient cycling.

Cation Exchange Capacity (CEC)

  • CEC reflects soil's ability to hold nutrients (cations) exchangeable at surfaces.
    • Influenced by clay type, organic content, and pH levels.
    • Key to maintaining fertility across soil types.
    • Techniques for determining include various soil samples and estimates based on soil chemistry.

Soil Acidity and Fertility Management

  • Acidity defined by free H+ concentration, critical for nutrient availability.
  • Liming: process to raise pH and enhance nutrient uptake by altering exchange capacities.
  • Soils present a range of pH preferences for optimal crop growth, affecting nutrient dynamics, particularly phosphorus.

Organic Matter in Soil

  • Organic Matter Composition:
    • Includes living organisms, decaying material, and humus.
  • Functions of Organic Matter:
    1. Improves soil structure and aeration.
    2. Enhances water retention.
    3. Serves as a reservoir for nutrients.
    4. Supports the microbes that contribute to organic cycling and health of the ecosystem.
    5. Impacts on the soil carbon/nitrogen balance.
  • Stability and Protection: Factors influencing decomposition rates and retention of OM.

Soil Fertility and Productivity

  • Fertility vs. Productivity:
    • Fertility: Nutrient provision capacity to sustain plant growth.
    • Productivity: Actual output levels achieved in crop yields.
  • Fundamental for agricultural practices to sustain soils for long-term cropping success.