Soil properties and its pollution

Soil definition (Geologic)

Loose surface of the earth as distinguished from solid bedrock. Plant life support not required.

Soil definition (Traditional)

Material that nourishes and supports growing plants, including rocks, water, snow, and air.

Soil definition (Component)

Mixture of mineral matter (45%), organic matter (5%), water (25%), and air (25%). Example: Loam soil.

Basic Soil Properties (Physical)

Texture, structure, bulk density, moisture, infiltration, porosity.

Basic Soil Properties (Chemical)

Nutrient content, salinity, pH, organic matter, mineral content.

Basic Soil Properties (Biological)

Microbial activity, biomass, biodiversity, biological activity.

Soil Texture

Relative proportions of sand, silt, and clay. Determines feel: gritty (sand), soft/silky (silt), sticky (clay).

Sand Characteristics

Gritty feel, 2:0.05,particles visible to naked eye, low water/nutrient retention, high drainage.

Silt Characteristics

Soft/floury feel, medium particle size (0.002–0.05 mm), moderate water/nutrient retention.

Clay Characteristics

Sticky feel, smallest particles (<0.002 mm), high surface area (10,000x sand), high water/nutrient retention.

Hydrometer Method

Lab technique to determine soil texture. Measures relative particle density in liquid after settling.

Hydrometer Formulas

% Clay = (R1/Wt soil) × 100

% Silt = (Rsilt”R2-R1”/Wt soil) × 100

%Sand = 100 - (%clay+%silt)

Soil Aggregates

Secondary soil units held by organic substances, clays, etc. Stability indicates OM content, biological activity, and erosion resistance.

Soil Horizons (A)

Topsoil: high organic matter, biological activity, N/P content, granular structure.

Soil Horizons (B)

Subsoil: silicate clays, iron/aluminum oxides, less OM, sub

Soil Horizons (C)

Parent material layer, minimally weathered.

Nitrogen Deficiency Symptoms

Yellowing of lower leaves (inverted “V” in corn), stunted growth, small ears.

Phosphorus Deficiency Symptoms

Bluish

Potassium Deficiency Symptoms

Brown leaf margins (corn), yellowing lower leaves (soybeans), striped appearance.

Soil Erosion Definition

Process where soil is moved from its original location by wind, water, or human activity.

Sheet Erosion

Uniform removal of topsoil by wind/water.

Rill Erosion

Small channels formed by surface water flow.

Gully Erosion

Severe erosion with deep channels due to intense rainfall.

Splash Erosion

Caused by raindrop impact disrupting soil structure.

Tunnel Erosion

Subsoil washing away beneath stable topsoil, creating hollows.

Causes of Soil Erosion

Overgrazing, deforestation, poor farming practices, slope length, low vegetation cover.

Heavy Metals (Toxic)

Pb, Cd, Hg, As. Harmful even in small amounts.

Heavy Metals (Essential)

Co, Cu, Fe, Mn, Mo, Ni, Zn. Required in trace amounts.

Bioremediation

Using plants/microorganisms to clean polluted soils. Example: Phytoremediation for heavy metals.

Phytoextraction

Plant

Effects of Soil Pollution

Reduced fertility, loss of nutrients, increased erosion, toxic dust, ecosystem imbalance.

Nitrogen Cycle Processes

Nitrification (NH4 → NO3), Denitrification (NO3 → N2 gas), Leaching, Volatilization (NH3 loss).

Control of Soil Pollution

Reduce chemical fertilizers/pesticides, recycle materials, afforestation, awareness programs.

Soil Salinity Impact

High salinity makes soil unfit for cultivation, often due to excessive fertilizers.

Organic Matter Role

Improves soil structure, water retention, nutrient cycling, and microbial activity.

Cation Exchange Capacity (CEC)

Soil’s ability to hold cations (e.g., Ca, Mg, K). Higher CEC = higher nutrient retention.

Ideal Soil Balance

45% minerals, 25% water, 25% air, 5% organic matter.

Denitrification Conditions

Occurs in waterlogged, anaerobic soils. Converts NO3 to N2 gas.

Volatilization Triggers

High temperatures, windy conditions, surface

Soil Pollution Sources

Industrial waste, agrochemicals, oil spills, nuclear waste, deforestation.

Degrees of Erosion

Slight (surface loss), Moderate (surface removed), Severe (subsoil exposed), Extreme (deep subsurface loss).

Calcium Role in Plants

Strengthens cell walls, promotes root growth, improves soil acidity.

Magnesium Role in Plants

Key in chlorophyll production, activates enzymes, aids phosphorus mobility.

Zinc Deficiency Symptoms

Bleached leaf bands (corn), stunted growth, high pH exacerbates.

Iron Deficiency Symptoms

Interveinal chlorosis in young leaves, common in high

Bulk Density

Soil weight per volume. High density indicates compaction, poor porosity.

Field Capacity

Maximum water soil retains after drainage. Wilting point = moisture level where plants cannot recover.

Available Water Capacity

Maximum amount of water available for plant that soil can provide

Wilting point

Moisture of soil soil at which plant wilt and failed to recover

Soil Pollution Human Health Effects

Kidney damage (Hg, Pb), liver changes (solvents), cancer risks (PAHs, pesticides).

Soil Conservation Methods

Contour farming, windbreaks, crop rotation, stabilizing roads with barriers.

Mycorrhizal Fungi Role

Symbiotic fungi aiding nutrient uptake, used in heavy metal remediation.

Sodic Soils

High sodium content displaces Ca/Mg, reduces fertility and structure.

Soil Pollution by Agrochemicals

Excess fertilizers alter pH, pesticides persist in food chain.

Soil Profile

Vertical section showing horizons (A, B, C). Indicates soil development over time.

Soil Texture Triangle

Classifies soil types based on sand, silt, clay percentages.

Humus

Decomposed organic matter enhancing soil fertility and structure.

Lateritic Soil Identification

High in iron oxides, reddish color, low fertility, suitable for crops like cassava.

Soil pH and Phosphorus

Availability highest near neutral pH (6.5–7.0). Fixed by Fe/Al (low pH) or Ca (high pH).