Soil science

Soil science studies how soil forms, what it is made of, how it behaves, and how it supports life. The field has two broad branches. Pedology studies soil in its natural setting, including its origin, classification, and distribution across landscapes. Edaphology studies how soil influences living things, especially plants, and how people use it to grow food. Soil science related content is to be organized and developed here.

What soil is and how it forms

Soil forms slowly from weathered rock and decaying organic material. Soil scientists usually describe five factors that shape any soil: parent material, climate, organisms, relief (the shape and slope of the land), and time.

As soil develops it separates into layers called horizons. A vertical cut through these layers is a soil profile. A common simplified sequence is an organic layer at the surface, a dark topsoil rich in organic matter, a subsoil where clay and minerals accumulate, and weathered parent material below. The layers record the history of the site.

Several properties describe how a soil behaves:

Texture is the proportion of sand, silt, and clay particles. It controls drainage and how much water and nutrients the soil holds.
Structure is the way particles clump into aggregates. Good structure leaves pores for air, water, and roots.
Organic matter is the living and decaying material in soil. It is a small share of most soils by weight, yet it strongly affects fertility and water holding capacity.
The soil food web includes bacteria, fungi, protozoa, nematodes, earthworms, and insects. They break down residues and release nutrients to plants. The zone around roots, the rhizosphere, is especially active.
Nutrient cycling moves nitrogen, phosphorus, and other elements between soil, organisms, water, and air.

Why soil matters

According to the Food and Agriculture Organization of the United Nations (FAO), about 95 percent of the food people eat is produced directly or indirectly in soil. Soil also filters and stores water and supports much of the biodiversity on land.

Soil is a major carbon store. The FAO states that, on a global scale, the top 30 cm of soil contains more carbon than the atmosphere and vegetation combined.

Soil is also easy to lose and slow to replace. FAO materials prepared for its Global Symposium on Soil Erosion state that it can take up to 1,000 years to produce just 2 to 3 cm of soil, that about 33 percent of the soils of the Earth are already degraded, and that accelerated erosion on arable or intensively grazed land is estimated at 100 to 1,000 times natural rates. Erosion, compaction, salinization, and nutrient depletion all reduce the ability of land to grow food.

Soil as slow-renewing infrastructure

In energy or computing, costs can fall quickly as technology improves. Soil behaves differently. It works like infrastructure that was built over centuries and cannot be rebuilt on a human timescale. A field can lose in decades topsoil that took many lifetimes to form. That mismatch makes soil a quiet limit on food abundance.

The most valuable soil work is often maintenance rather than invention. Cover crops, no-till farming, crop rotation, compost, and biochar aim to protect the existing asset and slowly rebuild organic matter. Better information also helps: soil testing, public soil survey maps, and remote sensing from satellites and drones show where soil is thin, eroding, or low in nutrients.

Another path reduces how much food depends on field soil at all. Urban farming, greenhouses, and indoor vertical farms grow some crops in small spaces, often without soil. Microbial and fermentation based foods go further. These approaches can take pressure off fragile land, but most staple crops still depend on fields. For the foreseeable future, protecting soil remains part of any serious plan for durable abundance, much like repairing tools instead of discarding them.

Core ideas

Pedology and edaphology
Soil formation factors
Horizons and profiles
Texture and structure

Organic matter and humus
Soil food web
Rhizosphere
Nutrient cycling

Erosion and degradation
Soil carbon
Soil health
Soil survey and mapping

Projects and resources

Learning materials and learning projects can be used by multiple departments.

This wiki has adopted an applied model for education. Lessons should be centered around active learning.

Select a descriptive name for each new link. See naming conventions.

Learning activities

Jar sedimentation texture test. Shake a soil sample with water in a clear jar and let it settle. Sand settles first, then silt, and clay last. The layer thicknesses give a rough texture estimate to place on a soil texture triangle.
Compost observation. Keep a small compost pile or bin and record temperature, moisture, smell, and visible organisms each week.
Local soil survey map lookup. In the United States, the Web Soil Survey lets anyone outline an area and read the mapped soil types, drainage classes, and limitations. Learners can compare the map with a hand-dug hole.

Discussion questions, essay ideas, and learning related AI prompt ideas

Discussion questions:

If soil forms so slowly, should it be treated as a renewable or a nonrenewable resource?
Which matters more for long term food supply: higher yields per hectare or protecting the soil that produces them?

Essay ideas:

Soil as infrastructure: how slow renewal shapes the limits of food abundance.
The role of public soil maps and data in decisions about land use.

Learning related AI prompt ideas:

"Explain the five soil formation factors with one example landscape for each."
"Help me interpret the results of a jar sedimentation test and place my sample on the soil texture triangle."

Readings

Soil science

External links

Last checked: October 2026