Soil as a Natural Resource

Soil

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

• pedalogy

  • 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

Soil forms through the accumulation and decay of organic matter and through physical, biological, and chemical weathering processes

Weathering

• process that breaks down rocks and minerals into smaller pieces

Physical Weathering

• mechanical breakdown of rocks without changing their chemical composition

  • examples:

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 Factoes

• 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: humans or organic matter

  • A-Horizon: topsoil, rich in minerals and organic matter

  • B-Horizon: subsoil, contains leached materials

  • C-Horizon: weathered parent material

  • R-Horizon: regolith, bedrock

• soil profile: cross-sections, showing soil horizons

Soil Formation

Soil Texture

Loam

• sand: 40%, silt: 40%, clay: 20%

• good drainage: allows water to drain well

• fertility: holds nutrients better than other soil but also provides better drainage

• structure: loose texture: important for root development

• pH: neutral to slightly acidic

Soil Properties

Porosity

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

• more porous = more water it can hold

Permeability

• measures how easily fluids can flow through a material

Color

• black-brown: high organic matter

• red-orange: oxidized; high iron content

• yellowish-white: rich in clay minerals

• gray: high moisture

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: 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

• phosphorus

  • essential for seed and root development

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

• potassium

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

  • low K: stunted growth, weak stem

Soil Problems

Soil Degradation

• 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

• 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

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

• causes

  • deforestation

  • human mismanagement of soil

Desertification

• conversion of agricultural croplands to deserts (cropland abandonment)

• causes

  • drought

  • deforestation

  • over cropping

  • mining

  • poor agricultural practices

Soil Conservation and Restoration

Composting

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

• compost - good soil conditioner

Alternative Pest Control

• 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 leads to soil infertility

  • depletes the natural nutrients of the soil faster

• multi-cropping

  • various crops in one field

• crop rotation

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

Contour Plowing & Terracing

• prevent soil erosion

• contour plowing

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

• terracing

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

Reforestation & Afforestation

• reforestation

  • replanting of trees in a previously forested area

• afforestation

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