Soil

**Importance and Functions of Soil**:
– Soil is crucial for Earth’s ecosystems, impacting various environmental factors such as ozone depletion, global warming, rainforest destruction, and water pollution.
– It serves as a significant carbon reservoir affected by human disturbance and climate change.
– Soil functions as a growth medium for plants, stores and purifies water, and regulates water quality.
– It plays a crucial role in the carbon cycle, converting dead organic matter into nutrients for plants and animals.
– Soil is an ecosystem with strong internal connectedness, involving physical, chemical, and biological processes.

**Soil Composition and Formation**:
– Soil is composed of water, gases, sand, silt, clay, and organic matter.
– Soil evolution leads to the formation of soil horizons with distinct properties (A, B, and C layers).
– Soil texture is defined by the proportions of sand, silt, and clay particles.
– Soil is formed through the accumulation of organic matter and movement of colloids, influenced by factors like parent material, climate, topography, organisms, and time.
– Soil development involves the alteration and movement of materials within the soil profile, leading to the formation of distinctive soil horizons.

**Soil Physical Properties and Characteristics**:
– Important physical properties include texture, structure, bulk density, porosity, consistency, temperature, color, and resistivity.
– Soil texture is determined by the proportions of sand, silt, and clay particles.
– Soil structures called peds or aggregates are formed from soil separates.
– Soil porosity, consistency, temperature, color, and resistivity affect aeration, water infiltration, and storage in the soil.
– Soil moisture levels such as saturation, field capacity, wilting point, and available water capacity are crucial for plant survival.

**Soil Biodiversity and Nutrient Availability**:
– Soil hosts a vast array of microbes, animals, plants, and fungi, estimated to be home to a significant percentage of Earth’s species.
– Nutrients for plants are supplied by soil, held in place by clay and organic matter.
– Nutrient availability is affected by soil pH and is recycled through living organisms, plant and microbial residues, mineral-bound forms, and the soil solution.
– Soil biodiversity is challenging to study due to the invisibility of most life forms.
– Various animals and insects have a significant presence in soil ecosystems.

**Soil Chemistry and Exchange Capacities**:
– Soil chemistry influences plant nutrient availability, physical properties, and living populations.
– Cation and anion exchange capacities moderate soil pH, alter structure, and purify water.
– Cation exchange capacity measures the exchangeable cations in soil, while anion exchange capacity allows soil to attract and release anions.
– Soil reactivity, measured by pH, affects nutrient availability and plant growth.
– Base saturation percentage is crucial for understanding soil fertility and nutrient availability, impacting plant growth.