Soil as a Natural Resource

Soil

natural body comprised of solids (minerals and organic matter), liquid, and gases

Pedology

science dealing with the study of soils

Pedogenesis

deals with soil formation or soil origin

Importance of Soil

• supports plant growth

  • contains nitrogen, phosphorus, potassium, and other bio elements

• habitat for animals and microorganisms

• essential for water filtration

Weathering

process that breaks down rocks and minerals into smaller pieces

Physical Weathering

mechanical breakdown of rocks without changing their chemical composition

Chemical Weathering

• involved the chemical alteration of minerals within the rock

• ex: Chocolate Hills, Philippines

Biological Weathering

involves the breakdown of rocks by living organisms

Soil-Forming Factors

• parent material

  • rocks from which the soil derived

• climate

  • temperature and rainfall impact soil formation

• time/age

  • time of formation

• topography

  • differences in land elevation and slipe

  • high elevations = dry and thin soil

• biota

  • plants, animals, and microorganisms contribute to soil structure and nutrient cycling

Soil Horizon

distinct horizontal layers of soil

O-Horizon

• top-most layer in the soil horizon

• humans or organic matter

A-Horizon

• second layer in the soil horizon

• topsoil, rich in minerals and organic matter

B-Horizon

• third layer in the soil horizon

• subsoil, contains leached materials

C-Horizon

• fourth layer in the soil horizon

• weathered parent material

R-Horizon

• fifth layer in the soil horizon

• regolith, bedrock

Soil Profile

cross-sections, showing soil horizons

Soil Properties: Porosity

• percentage of a material’s volume that is pore space

• more porous = more water it can hold

Soil Properties: Permeability

measures how easily fluids can flow through a material

Soil Properties: Color

• black-brown: high organic matter

• red-orange: oxidized; high iron content

• yellowish-white: rich in clay minerals

• gray: high moisture

Soil Properties: pH

• determines the type and growth of plants that can thrive in it

• solubility of some minerals needed for plant growth are pH dependent

• common soils: 4 to 2

ideal pH of soil

6.5-7.5

Soil Nutrients: Nitrogen

• needed by plants for cell-formation

Nitrogen Deficiency

• yellowish brown colors along veins and tips of leaves, stunted growth, pale color of older leaves

Soil Nutrients: Phosphorus

• essential for seed and root development

Low Phosphorus

• stunted growth, late maturity of plants; weak plants with purple streaks in the stems

Soil Nutrients: Potassium

• essential for strong and sturdy stems and advances root growth, resists diseases

Low Potassium

• stunted growth, weak stem

Soil Degradation (Soil Problems)

• decline in the quality and health of soil → loss of its ability to support healthy plant growth and perform essential ecological functions

• causes

  • intensive farming practices (excessive tilling, overuse of chemical fertilizers)

  • inadequate soil conservation measures

Laterization (Soil Problems)

• characterized by the intense weathering of rocks and minerals

• forms laterites: high in iron and aluminum oxides but low in nutrients

• cause: deforestation (exposes the soil, minerals are washed away)

Soil Erosion (Soil Problems)

• removal of topsoil → leads to thinning of soil, loss of nutrients and fertility → use of more fertilizers

• causes

  • deforestation

  • human mismanagement of soil

Soil Desertification (Soil Problems)

• conversion of agricultural croplands to deserts (cropland abandonment)

• causes

  • drought

  • deforestation

  • over cropping

  • mining

  • poor agricultural practices

Composting (Soil Conservation and Restoration)

• decomposition of organic waste by microorganisms into CO2, water and humans

• compost - good soil conditioner

Alternative Pest Control (Soil Conservation and Restoration)

• crop rotation and mixed crop cultivation to distrust life cycles of pests

• biological controls (ex: wasps, mantis)

• biogenetics (pest-resistant plants)

• use of biopesticides

Crop Rotation & Multi-Cropping: Monoculture (Soil Conservation and Restoration)

• leads to soil infertility

• depletes the natural nutrients of the soil faster

Multi-Cropping (Soil Conservation and Restoration)

• various crops in one field

Crop Rotation (Soil Conservation and Restoration)

• different crops in the same field over a period of time

Contour Plowing (Soil Conservation and Restoration)

• prevent soil erosion

• plowing and planting across the slope of the land, following its natural contours

Contour Plowing: Terracing (Soil Conservation and Restoration)

creating flat areas or “steps” on a slope to create level platforms for planting

Reforestation

• replanting of trees in a previously forested area

Afforestation

establishing a forest in an area where there was no forest before