Soil Science Cheat Sheet

The core ideas of Soil Science distilled into a single, scannable reference — perfect for review or quick lookup.

PiqCue — piqcue.com/soil-science/cheatsheet

Quick Reference

Soil Horizons

Distinct horizontal layers within a soil profile, each differing in color, texture, structure, and chemical composition. The major horizons are O (organic), A (topsoil), E (eluviation), B (subsoil), C (parent material), and R (bedrock).

Soil Texture

The relative proportions of sand, silt, and clay particles in a soil sample. Texture governs water-holding capacity, drainage, aeration, and nutrient retention, and is classified using the USDA soil texture triangle.

Cation Exchange Capacity (CEC)

A measure of a soil's ability to hold and supply positively charged nutrient ions (cations) such as calcium, magnesium, potassium, and ammonium. Higher CEC indicates greater fertility potential.

Soil Organic Matter (SOM)

The fraction of the soil composed of plant and animal residues at various stages of decomposition, along with living microbial biomass. SOM improves soil structure, water retention, nutrient supply, and biological activity.

Pedogenesis

The natural process of soil formation through the weathering of rock and the accumulation and transformation of organic material over time, driven by the five soil-forming factors: climate, organisms, relief, parent material, and time.

Soil pH

A measure of the acidity or alkalinity of a soil solution on a scale from 0 to 14. Soil pH strongly influences nutrient availability, microbial activity, and plant growth, with most crops thriving between pH 6.0 and 7.5.

Nitrogen Cycle in Soil

The series of biogeochemical transformations by which nitrogen moves between the atmosphere, soil organic matter, and living organisms, including fixation, mineralization, nitrification, denitrification, and immobilization.

Soil Structure

The arrangement of individual soil particles (sand, silt, clay) into aggregates or peds of various shapes and sizes. Good structure creates pore spaces that facilitate root growth, water movement, and gas exchange.

Mycorrhizae

Symbiotic associations between soil fungi and plant roots in which the fungal hyphae extend the root system, enhancing uptake of water and nutrients (especially phosphorus) in exchange for carbon from the plant.

Soil Erosion

The removal and transport of topsoil by wind, water, or tillage, often accelerated by poor land management practices. Erosion degrades soil fertility, reduces agricultural productivity, and causes sedimentation in waterways.

Key Terms at a Glance

Aggregate:A cluster of soil particles bound together by organic matter, clay, and microbial secretions, forming the basic unit of soil structure.

Alluvial Soil:Soil deposited by flowing water, typically found on floodplains and river deltas. Often fertile and well-suited for agriculture.

Bulk Density:The mass of oven-dry soil per unit of total volume, including pore space, expressed in grams per cubic centimeter.

Cation Exchange Capacity:A quantitative measure of a soil's ability to adsorb and release positively charged ions, expressed in centimoles of charge per kilogram of soil.

Clay Mineral:A phyllosilicate mineral with particle size less than 0.002 mm. Common types include kaolinite, montmorillonite, and illite, each with different properties affecting soil behavior.

Compost:Decomposed organic material produced through aerobic biological decomposition of plant and animal residues, used as a soil amendment to improve fertility and structure.

Denitrification:The microbial reduction of nitrate to gaseous nitrogen compounds under anaerobic conditions, resulting in nitrogen loss from the soil system.

Edaphology:The branch of soil science concerned with the influence of soils on living things, particularly plants and agriculture.

Eluviation:The removal of dissolved or suspended material from a soil layer by the movement of water, particularly the loss of clay, iron, and organic matter from the E horizon.

Field Capacity:The amount of water a soil holds after excess water has drained away by gravity, representing the upper limit of water available for plant use.

Humus:The stable, dark-colored organic material remaining after extensive decomposition of plant and animal residues. Highly resistant to further breakdown and critical for nutrient retention.

Illuviation:The accumulation of dissolved or suspended soil material in a lower horizon (typically the B horizon) after being transported downward from upper horizons.

Leaching:The removal of soluble materials from soil by percolating water, transporting nutrients and contaminants downward through the profile.

Loam:A soil textural class with a balanced mix of sand, silt, and clay, generally considered ideal for agriculture due to good drainage, moisture retention, and nutrient supply.

Mineralization:The conversion of organic nutrients into inorganic, plant-available forms through microbial decomposition of soil organic matter.

Get study tips in your inbox

We'll send you evidence-based study strategies and new cheat sheets as they're published.

We'll notify you about updates. No spam, unsubscribe anytime.