Living Off the Land: Soil Science and Sustainability

This set explores global land use statistics, the physical and chemical functions of soil, its composition and weathering processes, and modern threats such as erosion and salinization alongside sustainable agricultural solutions.

Habitable land

$76\%$ of Earth's land surface, totaling $107 \text{ Million } km^2$.

Agricultural land

$45\%$ of habitable land, totaling $48 \text{ Million } km^2$.

Physical support

A soil function where roots anchor themselves to keep plants upright and protected from high winds and flooding.

Ventilation

The soil's ability to allow for roots to have gaseous exchange involving $CO_2$ and $O_2$.

Soil habitat

A system harboring a wide range of organisms where biota play a vital role in soil development and nutrient cycling.

Soil organic carbon

Short-term carbon storage consisting of decaying plants, animals, feces, and microorganisms, representing a store of $2500 \text{ GT}$.

Humus

A component of soil representing long-term carbon storage that can last for millennia.

General composition of soil

Standard soil is composed of $45\%$ Mineral, $25\%$ Air, $25\%$ Water, and $5\%$ Organic material.

Physical Weathering

Soil development via thermal expansion/contraction, abrasion/exfoliation, and freeze-thaw cycles.

Chemical Weathering

The process where $CO_2$ in the air dissolves into carbonic acid and reacts with mineral grains.

Soil Horizons

The distinct layers of soil: O (Organics), A (Topsoil), B (Subsoil), and C (Parent Rock).

Clay

Soil particles with a grain size of $< 0.004\,mm$.

Loam

A soil type containing approximately $20\%$ clay that holds moisture for roots without causing drainage problems.

UK Soil Formation Rate

In the UK, it takes approximately $400 \text{ years}$ for $10\,mm$ of soil to develop.

Soil Sealing

A consequence of urbanization that prevents soil from accessing air and water.

Soil Stability

The resistance of the soil structure to external factors such as water.

Salinization

The buildup of salts in soil caused by water removal, prevention of flushing, or the addition of salt-rich irrigation waters.

Sustainable farming approaches

Methods that integrate natural processes like nutrient cycling, nitrogen fixation, and use of natural predation (e.g., ladybirds).

Zero-tillage

A sustainable farming practice involving the cessation of ploughing to maintain soil health.