Common Threats to Soil

Common Threats to Soil

• Soil degradation is caused by certain drivers, leading to various types of soil degradation with many ramifications.
• Soil and Agricultural Sciences offer a wide array of solutions for sustainable soil management.
• Drivers of soil degradation include deforestation, biodiversity loss, population growth, water scarcity, urban expansion, nutrient imbalance, compaction, pollution and waste disposal, climate change, sealing, food and nutrition insecurity, rapid climate change, poverty and social insecurity, acidification, unsustainable soil management practices, erosion, and migration.
• Types of soil degradation involves loss of organic carbon.
• Consequences of soil degradation include soil degradation, waste of ecosystem water services, and reduction of soil fertility.

Interrelations Between Soil Threats

• Drivers consist of applications of manure & fertilizers, pesticides & herbicides, sewage sludge, gravel extraction, and heavy metal release.
• Threats include sealing, gradual disappearance of farms, soil erosion, gradual destruction of soils, reduction in soil fertility, declining organic matter, changes in structure of soils, compaction and acidification.
• Consequences include contamination of soils and ground water from agrochemicals and atmospheric pollutants, changes in soil composition, adverse impacts on living organisms, and destruction of soil.
• Diffuse input of contaminants occur as particulates while other persistent substances includes acids and toxic substances.

Soil as a Three-Phase System

• Soil is a complex three-phase system made of solid (mineral and organic), liquid/moisture/water (dissolved nutrients), and gases/air (e.g., N2, O2, CO2).
• The magnitude and interaction among the three phases dictates the behavior and functionality of the soil.
• Proportions of each phase may vary but ideally consist of 50% solid, 25% liquid and 25% gas.
• Soil solids contain 45% minerals and 5% organic matter.
• Soil pore space contains 20-30% air and 20-30 water.

Basic Volume and Mass Relations of Soil Components

• An ideal soil contains 25% air, 25% water, 45% mineral particles, 5% organic matter broken down to 10% organisms, 10% roots, and 80% humus
• ρs = Ms/Vs (Solid density)
• ρb = Ms/Vtot = Ms/(Vs + Vw + Va) (Bulk density)
• ρbw = (Ms+Mw)/Vs (Wet density)
• θg = Mw/Ms (Gravimetric water content)
• θ = Vw/Vtot = θg *Pb (Volumetric water content)
• Se =Vw/Vp = Vw/(Va + Vw) (Degree of saturation)
• n = 1-Vs/Vtot (Soil porosity)
• n = 1-Pb/Ps (Soil porosity)

Pedosphere as Part of the Geosphere

• The vertical structure of the geosphere consists of the atmosphere, biosphere, geosphere, lithosphere, and hydrosphere.
• The oceans, flowing and standing waters belong to the hydrosphere.
• The pedosphere and lithosphere contains soil water and groundwater.
• Life exists up to 9 km high temporarily in the atmosphere (birds, insects).
• Life in the pedosphere exists up to 5 m deep (earthworms).
• Life in the deep sea exists up to 11 km deep.

Soil Forming Factors Equations

• S = f(cl, o, r, p, t) from Jenny (1941).
  • cl: climate.
  • o: organisms.
  • r: relief.
  • p: parent material, lithology.
  • t: time.
• Sc = f(s, c, o, r, p, a, n) from McBratney, et al., (2003).
  • s: soil.
  • c: climate.
  • o: organisms.
  • r: topography.
  • p: parent material, lithology.
  • a: age.
  • n: position.

Soil Forming Factors Breakdown

• Climate properties like temperature increases chemical reactions that breakdown rocks and minerals, In areas of high rainfall, water drains and leads to leaching minerals
• Organisms, burrowing animals, plant roots and actions of bacteria/fungi chemically alter and physically mix soils.
• Relief, topography: slope of direction landscape faces influences sunlight hours, temperature, water runoff, erosion and organic matter build-up.
• Parent Materials composition of unweathered rock dictates mineral content of soil.
• Time partly depends on age and older soils are more weathered, like tropics
• The CLORPT formula dictates that climate, organisms, relief, parent rock and time shape the soil
• The SCORPAN formula dictates that soil, climate, relief, organisms, parent rock, age and position shape the soil

Soil Forming Processes

• Soil underlies processes of 1) additions to a soil body, 2) losses from a soil body, 3) translocation within a soil body, and 4) transformation of material within a soil body.
• A natural equilibrium occurs when processes are balanced and lead to a permanent “refreshment” of the soil quality and quantity.
• Factors of soil forming processes include parent material, climate, topography, organisms, and time.
• Properties include morphological, physical, chemical, mineralogical, and biological.

Basic Soil Forming Processes.

• Soil addition (enrichment): adding nutrients or organic matter, from rain, dust, or rising groundwater.
• Soil losses (removal): removing soil from one area and transporting to another (soil erosion, nutrient uptake, evaporation, transpiration).
• Soil translocations (internal movement): eluviation (movement out of) and illuviation (movement into), e.g., minerals, clay, organic matter.
• Soil transformation (change in properties): decomposition, weathering, soil water freezes.

Soil Components and Processes

• Eluviation refers to the movement of material out of a portion of a soil profile.
• Illuviation refers to the movement of material into a portion of a soil profile.
• Leaching is the general washing out of soluble materials from the solum.
• Enrichment refers to the general addition of material to a soil body.
• Erosion, surficial refers to the removal of material from the surface layer of a soil.
• Cumulization refers to eolian, hydrologic and human-made additions of mineral particles to the surface of a solum.
• Decalcification is reactions that remove calcium carbonate from one or more soil horizons.
• Calcification processes result in the accumulation of calcium carbonate.
• Salinization refers to the accumulation of soluble salts.
• Desalinization is removing salts from soil.
• Lessivage is the mechanical movement of small mineral particles from the A to B horizons.
• Pedoturbation is the biological and physical churning of soil materials,
• Podzolization is the chemical migration of aluminum and iron and/or organic matter,
• Decomposition involves the breakdown of mineral and organic materials.
• Synthesis describes the formation of new particles of mineral and organic species.
• Melanization is the darkening of light-colored, initial materials by admixture of organic matter.
• Littering refers to the accumulation of organic litter and associated hummus.
• Humification transforms raw organic material into humus.
• Paludization includes the accumulation of deep deposits of organic matter as in mucks and peats
• Mineralization refers to the release of oxide solids through decomposition of organic matter.
• Braunification, rubification, describes the release of iron from minerals and the dispersion of particles of iron oxides or oxyhydroxides.
• Gleization refers to the reduction of iron under anaerobic soil conditions.
• Loosening involves an Increase in volume of voids by activity of plants, animals, and humans by removal of material or freeze thaw
• Hardening involves decrease in volume of voids by collapse and compaction.

Definitions

• Polypedon is a collection of Pedons that form a soil body.
• Pedon is the smallest 3D unit of soil (1 meter on each side).
• Soil profile is a vertical cross-section of the soil, with soil horizons (layers); from the soil surface to parent material or bedrock/water table/1.5 m.
• Soil solum is the A and B horizons, where the most active soil forming processes occur.

Soil Sampling Keypoints

• The process of taking a soil sample to be tested for the chemical, physical and biological properties
• There are undisturbed (native soil) and distributed samples points in soil sampling

Soil Distribution Factors

• There can be erosion (evlauation out) from steep slopes, shallow soil and low nutrient soil.
• Flat slopes and lower points typically represent high accumulation and high nutrient concentration.