Soil Resources

Earth System Spheres

The five interconnected subsystems of Earth: Biosphere, Atmosphere, Hydrosphere, Lithosphere, and Cryosphere.

Pedosphere

The Earth's envelope where soils occur and soil-forming processes are active.

Atmosphere–Pedosphere Interaction

Absorbs CO₂ and facilitates the nitrogen cycle by storing usable nitrogen forms for plants.

Biosphere–Pedosphere Interaction

Creates pores and channels for air and water and adds organic matter.

Lithosphere–Pedosphere Interaction

Provides parent material and mineral nutrients.

Hydrosphere–Pedosphere Interaction

Influences the solubility and availability of nutrients.

Geophagy

The habit of consuming Earth materials such as clay, soft stone, sand, termite mounds, and anthills.

Global Food Production

Over 95% of human food is directly or indirectly produced by soils.

Soil as a Carbon Sink

Most of the planet's carbon is stored in soil, including permafrost regions.

Soil Carbon Storage

Approximately 3,350 gigatons of carbon, significantly more than in the atmosphere or vegetation.

Global Soil Biodiversity

Soil is home to more than 50% of all species on Earth.

Soil–Human Health Connection

Soil contaminants transfer through the food web: plants → earthworms or grazing animals → humans.

Soil and Infrastructure

Proper soil foundation assessment is critical to preventing structural hazards and disasters.

Cherry Hills Landslide

A historical example illustrating the importance of proper soil and foundation assessment.

Soil Renewability

Soil is a non-renewable resource because its formation takes hundreds to thousands of years.

Soil Formation

Occurs through mechanical and chemical weathering over hundreds to thousands of years.

Soil Volume Composition

Soil consists of 50% solid particles and 50% pore space.

Solid Particles

Make up 50% of soil volume.

Minerals

Make up 45% of soil volume.

Organic Matter

Makes up 5% of soil volume.

Pore Space

Make up 50% of soil volume and contains air and water.

Air

Occupies 25% of soil volume.

Water

Occupies 25% of soil volume.

Soil Profile

A vertical sequence of soil horizons.

O Horizon

Organic layer consisting mainly of decaying organic material.

A Horizon

Topsoil rich in organic matter and nutrients.

B Horizon

Subsoil where minerals washed down from the topsoil accumulate.

C Horizon

Layer consisting of fragmented parent rock.

R Horizon

Unweathered parent rock, also called bedrock.

Soil Horizon Sequence

The vertical arrangement of soil layers: O, A, B, C, and R.

Soil Texture

The relative proportions of sand, silt, and clay particles in soil.

Sand

2.0 mm–0.05 mm; the largest soil particle.

Silt

0.05 mm–0.002 mm; the intermediate-sized soil particle.

Clay

Less than 0.002 mm; the smallest soil particle.

Porosity

The number of voids or pores per area.

Permeability

The capability of water to pass through soil.

Water-Holding Capacity

The ability of soil to retain water.

Primary Macronutrients

The three major plant nutrients: Nitrogen (N), Phosphorus (P), and Potassium (K).

Nitrogen (N)

Promotes new cell formation and rapid vegetative growth.

Phosphorus (P)

Supports seed and root development and blooming.

Potassium (K)

Helps build proteins, improves fruit quality, and increases disease resistance.

Secondary Macronutrients

Calcium (Ca), Magnesium (Mg), and Sulphur (S).

Micronutrients

Chlorine (Cl), Iron (Fe), Boron (B), Copper (Cu), Manganese (Mn), Zinc (Zn), Nickel (Ni), and Molybdenum (Mo).

Soil pH

Influences mineral solubility, nutrient availability, and suitability for plant growth.

Neutral Soil pH

Approximately 6.0–7.5; generally provides optimal availability of primary nutrients.

Soil Degradation

The deterioration of soil quality and productivity.

Water Erosion

Accounts for 56% of soil degradation.

Wind Erosion

Accounts for 28% of soil degradation.

Chemical Degradation

Accounts for 12% of soil degradation.

Physical Degradation

Accounts for 4% of soil degradation.

Primary Causes of Soil Degradation

Overgrazing, deforestation, agricultural activity, overuse of vegetation, and industrial activity.

Overgrazing

Accounts for 35% of soil degradation causes.

Deforestation

Accounts for 30% of soil degradation causes.

Agricultural Activity

Accounts for 27% of soil degradation causes.

Overuse of Vegetation

Accounts for 7% of soil degradation causes.

Industrial Activity

Accounts for 1% of soil degradation causes.

Agricultural Soil Erosion

Considered the single biggest soil problem associated with agriculture.

Land Clearing

Reduces topsoil and causes the loss of soil minerals and organic matter.

Waterlogging

Saturated soil conditions that create anaerobic conditions.

Denitrification

The nitrogen process that occurs under anaerobic conditions, such as waterlogged soil, instead of healthy nitrification.

Salinization

The accumulation of dissolved salts in topsoil as water evaporates, hindering plant growth.

Salinization in the Philippines

Observed in Tarlac.

Pesticide Treadmill

A cycle where pesticides kill pests, resistant pests survive and reproduce, and stronger or more pesticides become necessary.

Pesticide Treadmill Sequence

Pesticide application → Pest death → Genetic resistance develops → Stronger or more pesticides are needed.

High-Input Monoculture

Continuous planting of a single crop, depleting specific nutrients and increasing reliance on synthetic inputs.

Soil Conservation

Practices that protect soil from degradation and maintain its productivity.

Conservation Tillage

Reduces erosion, lowers evaporation, and enhances nutrient cycling.

Crop Rotation

Alternating different crops to prevent specific nutrient depletion and break pest cycles.

Multicropping

Growing multiple crops to help prevent nutrient depletion and break pest cycles.

Contour Cropping

Planting crops along slope contours to reduce water runoff and topsoil loss.

Strip Cropping

Planting crops in alternating strips to help reduce water runoff and topsoil erosion.

Terracing

Shaping sloped land into stepped platforms to slow water runoff.

Banaue Rice Terraces

A famous Philippine example of terracing.

Shelterbelts / Windbreaks

Rows of trees planted to reduce wind speed, soil evaporation, and wind erosion.

Erosion Control Plants

Plants used to stabilize soil and reduce erosion.

Vetiver (Chrysopogon zizanioides)

A deep-rooted grass commonly used for erosion control.

Integrated Pest Management (IPM)

A pest-control approach combining biological controls, physical traps, and minimized chemical use.

Biological Pest Control

Using natural predators, such as ladybugs, to control pests.

IPM and the Pesticide Treadmill

Reduces dependence on chemical pesticides by combining biological and physical pest-control methods.

Composting / Organic Waste Cycling

Recycling food waste into farm soil to rebuild humus and organic matter.

Humus

Organic material in soil that contributes to soil fertility and structure.