(477) APES Video Notes 4.3 - Soil Properties

Soil Composition and Properties

Introduction

  • Focus on the different properties that contribute to soil fertility.

  • Soil supports plant growth; its ability is determined by its composition.

Objectives

  • Describe similarities and differences between soil types.

  • Understand soil composition (sand, silt, clay) and their impact on water and nutrient retention.

  • Classify soils based on texture; know tests to evaluate soil fertility.

Soil Composition

  • Components of Soil:

    • Made up of rock fragments: sand, silt, and clay.

    • Contains organic matter, humus, water, and air.

Particle Size and Soil Texture

  • Weathering of Rock: Breaks down into sand, silt, and clay particles.

  • Characteristics Impact:

    • Particle size affects water and nutrient retention.

  • Porosity:

    • Refers to the amount of pore space between soil particles.

    • More sand = more porosity, allowing air and water to penetrate.

Soil Texture Chart

  • Classification of Soils:

    • Use a soil texture chart based on percentages of sand, silt, and clay.

  • Calculating Soil Texture:

    • Collect soil, let it settle in water, and measure layers.

    • Example:

      • 45% sand, 35% silt, 20% clay = loam.

  • Tips for Reading the Chart:

    • Start at bottom (sand percent), trace diagonally to where it meets silt, then find clay.

    • Ensure percentages add up to 100.

Porosity and Permeability

  • Porosity: More pore space allows easy water entry.

  • Permeability: Refers to how easily water drains through soil.

  • High porosity (sandy soil) = low water retention.

  • Balance needed for plant growth.

  • Ideal Soil Mix: Loam (40% sand, 40% silt, 20% clay) provides moderate drainage and water access.

Factors Affecting Soil Fertility

  • Nutrients:

    • Essential nutrients: nitrogen, phosphorus, magnesium, calcium, and potassium.

    • Organic matter enhances soil nutrient availability and water retention.

  • Clay and Nutrient Binding:

    • Negatively charged clay binds positive nutrients, retaining them in soil.

  • Acidity:

    • Acidic soils leach nutrients easily, harming fertility.

    • Excessive farming depletes nutrients without organic return

  • Topsoil erosion can further exacerbate these issues by removing the most fertile layer of soil, leading to reduced agricultural productivity and increased reliance on chemical fertilizers.

Water Retention and Aeration

  • Well-Aerated Soil: Supports more water and air retention due to channels created by organisms.

  • Effects of Structures:

    • Compacted soil = less moisture retention.

  • Organic Matter: Helps prevent evaporation.

Soil Quality Tests

  • Texture Assessment:

    • Settle soil in water to measure percentages for classification.

  • Permeability Test:

    • Time water drains through a soil column to assess retention.

  • pH Test:

    • Test for acidity using water and pH strips; lower acidity is better for plant growth.

  • Soil Color Test:

    • Compare soil to a chart; darker soil has more humus, indicating better nutrient retention.

  • Nutrient Level Measurement:

    • Chemical tests for nitrogen and phosphorus sources.

Practice Question (FRQ)

  • Identify a soil test.

  • Explain how results inform recommendations for crop production.

Conclusion

  • Importance of soil composition in supporting plant life.

  • Emphasize balanced soil properties for optimal agricultural practices.