soils 3210 preim

Definition of soil

The layer(s) of generally loose mineral and/or organic material that are affected by physical, chemical, and/or biological processes at or near the planetary surface and usually hold liquids, gases and biota, and support plants

Human reliance on soil

More direct

• Nutrients 

  • Plants

  • Animals that eat plants

  • Direct consumption (although rare)

• Building and energy

  • Brick and tile

  • Wood

  • Oil, gas and peat

    • Although oil and gas are usually much deeper than soil, they are decomposed in soil at some point

Less direct

• Natural water filter

• Organisms that support other life forms (Worms, microbes, etc)

• Climate moderation (C)

Soils are made of…

Pore space (water/air)

Mineral fraction

OM

Primary (abiotic) processes of soil building

1. Soil particles contain mineral nutrients

2. Particles allow for water retention (capillarity)

3. Dissolution of mineral nutrients (P, K, Ca, etc)

4. Mineral nutrients retained by soil

Secondary (biotic) processes of soil building

1. Invasion by plants and microorganisms. Capture of nitrogen and carbon, solar energy

2. Storage of organic carbon, nutrients and water

3. Decomposition of dead organic materials. Mineralization and release of nutrients and energy

Factors of soil formation CORPT

• Climate

• Organisms (grassland? forest?)

• Relief (topography)

• Parent Material (granitic, basalt)

• Time

CORPT

Soil health/soil well-being

“The continued capacity of the soil to function as a vital living ecosystem that sustains plants, animals, and humans”

• Function is a relative term

  • Some soils might not hit the peaks of others, not every soil can be Usain Bolt, but they can at least do their job decently well

Soil health effects

Humans affect soil health

Ancient civilizations and their staples

Fertile Crescent/Mesopotamia: wheat

Meso-America: maize

West South America: potatoes

North China Plain and Yangtze Delta: rice and soybean

First domestication of animals

Zagros mountains

Sheep, goat, cattle: easier to work with

Early soil management

Scratch plow + broadcast

Crop-livestock systems

Draft animals

• Entire crop was removed

  • Used straw, less desirable parts of plants for roofs, bricks, bedding, animal feed, etc

  • However: draws nutrients out of soil without putting anything back

Why were chinampas effective

• Water in canals absorbs sun’s radiation by day, radiates heat by night → helps protect against frost

• Raised beds moistened by capillary suction

• Nutrient rich sediment in canals becomes fertilizer

• Canals also useful for transportation

Who made New Horse Husbandry

• Jethro Tull (1674-1741) noticed that traditional sowing methods (broadcast) or in the furrow) provided low germination rates. He designed a drill with a rotating grooved cylinder that directed seeds to a furrow and subsequently covered them. Row seeding also allowed for mechanical cultivation

  • Row planting vs scattering seeds by hand: more opportunities for weed control, can cultivate weeds all in a row

• Tull, believing that plants absorbed small soil particles for nutrition, promoted repeated and intensive tillage to pulverize the soil as a substitute for adding manure. He grew wheat for 13 consecutive years without adding manure. He published his book titled The New Horse Hoeing Husbandry in 1731, which still has an impact today

6 Grand challenges to ag sustainability

• Population growth

• Meat consumption

• Declining Resources

• Soil degradation

• Climate change

• Agricultural Pollution

Green revolution technologies

• Transfer of improved crop varieties, irrigation, synthetic fertilizers, and pesticides to developing countries

• High yielding varieties of wheat and rice

  • DIsease resistance

  • Semi-dwarf varieties reduced lodging from fertilizer

  • Heavy reliance on chemical inputs

Digital agriculture

• Deployment of computational and information technologies to improve the profitability and sustainability of agriculture

• Offers opportunities through the ubiquitous availability of highly interconnected and data-intensive technologies

• Reflects a shift from generalized management of farm resources towards highly optimized, individualized, real-time, hyper-connected and data-driven management

• Data analytics, smart machines, system dynamics and optimization, biological and physical science

Soil water cycle

• Precipitation comes from above

• Reaches surface, infiltrates soil OR intercepted by (tree) canopy (maybe 10%, relatively minor) OR runs offs

  • Very critical - does it infiltrate or run off?

  • Runoff can reach streams very quickly 

• Soil Water storage

• Percolation

  • Relatively slow - water has to make its way through pores

  • To deep groundwater 

  • To stream

    • Very slow when coming from percolation - maybe comes 3 months later

• Evapotranspiration - losses

Soil water budget

• Precipitation + irrigation = interception + infiltration + runoff

  • Infiltration = ET + ΔSoil storage + percolation

    • ΔSoil Storage - soil can dry out (water leaving soil through gravity like a saturated sponge, etc), plants can use water

Rain and ET effects on percolation

Lower evapotranspiration with high rains means good amount of percolation

Return periods

• Planning for infrastructure development related to water requires an analysis of the recurrence of storms of different duration and intensity

  • T = 1 / P

  • Where T = return period in years

    • P = probability that an observed event in a given year is equal to or greater than a given event

    •  Basically, a 100 year event has a 1/100 chance of happening every year

  • Design of such structures focuses on the prediction of runoff during major hydrologic events

• Infrastructure may need to be built to deal with a 50 year event, or a 100 year event, etc

  • There is no memory: a 50 year event can happen twice in 2 weeks (November 2 and 16 2020, category 4 and 5 hurricanes)

Raindrop energy formula

• Raindrop energy: E = ½ m v²

  • m = mass (4/3 pi r³)

  • v = velocity

Drought Indices - percent of the normal

• It is calculated by dividing actual precipitation by normal precipitation – typically considered to be a 30-year mean – and multiplying by 100%. This can be calculated for a variety of time scales.

• If normal is 750ml, and we get 500ml, percent of normal is  66.666%

• Limitation to this index - If we say we got 60% of the normal, it doesn’t indicate WHEN it was dry - certain periods more important than others

Drought indices - standardized precipitation-evapotranspiration index

• WIth a value for PET, the difference between the P (precipitation) and PET (potential ET) for month i is calculated:

  • D_i = P_i - PET_i

• Provides measure of water surplus or deficit for the analyzed month.

  • The calculated D_i values are aggregated at different time scales as it relates to different drought-related concerns

    • Precipitation vs demand for water (through ET)

• The SPEI enables identification of different drought types and impacts in the context of global warming

Traits of areas prone to desertification (and examples)

• Low precipitation, high evaporative demand

• Extreme variation in rainfall (within and between years)

• Poor soils with low inherent fertility and poor physical properties

• Limited plant cover

• Low carrying capacity

  • These factors result in highly fragile ecosystems. Land is susceptible to degradation from intensified land use, often as a result of inappropriate technological and social advances. Such land degradation results in an irreversible reduction in land productivity and ability to support vegetation. Use of groundwater is often unsustainable

Middle east/western Asia

Sahara

Australia

Central/Western US

Particle density ρ_p

M_solid / V_solid

OM: <1 g/cm³

Quartz: 2.65 g/cm³

Bulk density ρ_b

M_solid / V_total 

Normal soil bulk densities: 1.0-1.6 g/cm³

Affected by soil texture, mineralogy, organic matter content, and compaction level (aggregation)

Bulk density meanings (higher vs lower)

Lower bulk density - lower weight, more pore space

Higher bulk density - higher weight, less pore space

Forces acting on soil

Capillary forces - cohesion and adhesion

Gravity

Osmosis - across membranes

Capillary forces

• Hold water between soil particles

• Soil is negatively charged: bipolar water molecules can hold onto soil

• Cohesive forces:

  • Hydrogen bonding

  • Van der Waals - London forces

  • Results in surface tension

    • Water tends to minimize the air-water interface because of cohesion. Water molecules at the surface experience a net inward force

• Adhesion results from double-layer forces

• Capillarity: combined effects of cohesion and adhesion

  • Consider the behavior of water drops on a glass plate. (glass and soil particles, particularly quartz, have similar chemical compositions)

  • Without gravity, and neglecting adhesion to the glass plate, a volume of water forms a sphere due to internal cohesion and surface tension

  • Gravity and adhesion distort the sphere into roughly a hemisphere

  • As the plate is tilted, cohesive forces resist distortion from the hemispherical shape (flow), and adhesion resists the downhill pull of gravity

  • As the plate is tilted further, gravity overcomes viscosity and the drop begins to flow. The “point” of the characteristic teardrop is due to adhesion (wetting)

Adsorbed/hygroscopic water properties

• Capillary water coheres to adsorbed water and to itself. Surface tension produces the curved water-air interface. The smaller the radius of the curve, the more tightly the water is held in the pore (higher suction)

  • Smaller pores are water filled, which larger pores are partially drained

Capillary tube formula

• h = 2γ / r

• γ = surface tension constant

• r = radius

• h = height of water column

• A simple rule, when all units are in mm:

  • h = 15/r or r = 15/h

Gravimetric water content

w = M_water / M_solids

Volumetric water content

θ =  V_water / V_total

w and θ relation through bulk density formula

θ = w * ρ_b

• Volumetric water content = gravimetric water content * bulk density

Soil water potential, energy status of water in soil

•  The total (net) potential in a soil region is composed of several component potentials:

  • Ψ_t = Ψ_g + Ψ_p + Ψ_o

  • Ψt =  total soil water potential

  • Ψg = gravitational potential

  • Ψp = pressure (matric) potential

  • Ψo = osmotic potential

Water in soil profile: how does it drain? Matric potential above vs below water table

• Sequentially smaller pores are drained as the soil dries out

• Lower soil section is saturated (below the water table)

  • Under the water table - pressure equivalent to the water above you, Ψ_p > 0

  • Above water table - pressure becomes negative due to positive suction (capillarity) Ψ_p < 0

  • At water table: 0 pressure, Ψ_p = 0

Soil-atmosphere-plant continuum

• ET dries out the soil and decreases Ψ_p

Field capacity

Theoretically: amount of water held by soil (due to capillarity) against gravity

• Laboratory measurement: soil water content at -33kPa; for sand, -10kPa

• Field capacity in the field depends on: soil texture (clay: 4-5 days, sand <1 day free drainage), type of clay, organic matter, depth to water table, depth of soil, surrounding topography, presence of layers in the soil, and time of measurement

Permanent wilting point

• Soil water content at which the plants can no longer recover turgidity (they wilt)

• PWP indicates the lower limit of water availability. Depends on plant properties, soil properties, meteorological conditions

• Generally, PWP is assumed to be the soil water content at a suction of 150m (Ψ_o = -1.5MPa). In reality, plant water stress occurs at much lower (less negative) suctions and depends on meteorological conditions

  • Irrigation of crops is often initiated at much lower suctions, before water stress occurs: (Ψ_p = 0.05 - 0.07 Mpa)

Why is soil aggregation important

• A well aggregated soil has a range of pore sizes that support multiple hydraulic functions

  • Small pore: long term moisture retention

  • Intermediate pore: Important for water retention and biological functions

  • Large pore: Important for drainage, aeration and rooting

STORAGE and DRAINAGE DEPENDS ON AGGREGATION

Poisseulle’s Law:

• Flux through a pore is proportional to the fourth power of the radius of the tube

• Flux through a pore is proportional to the pressure difference

• Q = ΔΨ_p/L * πr⁴

  • Q = water flux (mm/s)

  • ΔΨ_p / L = pressure gradient

  • r = radius of the pore

  • Flux density (flux per unit area):

    • q = Q/area

    • Q~r²

Hydraulic conductivity

• At the macroscopic level, a multitude of flow tubes in soil are represented by one value, the hydraulic conductivity, K, also referred to as permeability

  • Inverse of resistance, analogous to Ohm’s Law in electronics, I = V/R

  • Saturated hydraulic conductivity (K_s): the soil’s ability to conduct water under unit gradient when all pores are filled with water

• K-values lower for compacted soils

Infiltration rate graph

• Dry and well structured soils have better infiltration at first, but eventually converges with the slope of the wet, well structured soils

• Dry, compacted soils have poor infiltration, quickly have infiltration rate fall under the rainfall rate

  • Wet compacted soils have infiltration rate under rainfall rate immediately

• Surface pounding: when infiltration rate is lower than rainfall rate, ponding and runoff occurs

Philip’s equation

• Infiltration rate: i = S*t^-0.5 + A

• Cumulative infiltration: i*t = l = S*t^0.5 + A*t

  • i = infiltration

  • t = time

  • l = cumulative infiltration

  • A = transmissivity, final infiltration rate

Factors affecting infiltration

• Soil type

• Aggregation/crusting/sealing

  • Crusting - when pores on surface are not abundant, and soils fall apart with enough pressure (think of lawn demonstration)

• Surface storage capacity

  • Water that collects on surface but doesn’t runoff or infiltrate quickly

  • Retained in basins of mulch

• Plant canopies

  • Intercept energy from raindrops, and suction of water

• Surface cover and mulch

  • Absorb force of rain hitting the ground

• Soil freezing

• Hydrophobicity

  • A tabletop is hydrophobic, doesn’t absorb water; in soils, typically refers to organic matter and surface tension

  • After fires, soil is very hydrophobic; more potential for runoff

Soil freezing

• Moisture tied up as ice near surface and clogs pores

• Water infiltration rate very low (or zero), high runoff risk

• Soil under frozen layer dry (friable)

• Surface ice supports heavy equipment; low compaction

• Ice lenses break up compaction

• Frost tillage: tilling soil with shallow frozen layer (3-7 cm)

Soil thawing

• Soil thaws from surface down

• Thaw water initially cannot enter the soil and creates supersaturated conditions

• High potential for runoff and erosion (especially of concern with surface applied manure), and nitrous oxide losses

• Water quickly enters into dry lower layers after frost disappears

  • Frost seeding: spreading seeds (e.g. clover) over frozen soil which subsequently mix with supersaturated soil (liquid consistency) during early soil thaw

Watershed (catchment)

a unit of land from which surface, subsurface, and groundwater runoff flow to a common outlet
Larger ones are called basins

Orders of streams/watersheds

When two of the same order combine, they will become a higher order

• Defined by how many streams come together

• 1: first order stream, convergence of two flows

• 2:  second order stream, convergence of two first order streams

• 3: third order stream, convergence of two second order streams

NYC drinking water supply watersheds

• Croton watershed used since 1842

  • 2 centuries of development with 25-50 year plans; some of the best-tasting and safest water of any urban area; no water treatment (saved $3-5B)

Runoff hydrograph

• Typically: base flow without rain, then runoff volume can vary with rain intensity, then a peak runoff rate

Note: base flow may not be present

• In small ephemeral streams/waterways

• After long dry periods

Hydrologically sensitive areas for runoff surface losses

areas with great potential for transporting pollutants to surface or groundwater.

definition related to the transport mechanism:

1. For runoff surface losses these include:

   1. flood plains

   2. areas adjacent to flowing and standing water bodies

   3. areas with low infiltration capacity (paved, compacted or bare surfaces)

   4. saturated areas

Hydrologically sensitive areas for leaching

1. For subsurface recharge (leaching) these include:

   • groundwater recharge areas near wells or springs

   • saturated areas and wetlands

   • areas with very permeable soils

Soil organic matter

Complex mixture of organic substances, including plant and animal residues at various stages of decomposition

All material in soils that contains (reduced) carbon is SOM

What % of SOM is SOC

50-65

Main ingredients of organic matter

CHNOPS

Living SOM

• bacteria fungi nematodes earthworms mites springtails protozoa plant roots

• ROles: make nutrients available, nutrient acquisition, suppress disease, aggregate soils

Dead SOM

• Manure, winter-killed crops, partially decomposed fresh residue: stems, roots, and fungi

Roles:

• Provide food (energy and nutrients) for soil organisms to live and function

• Organic matter that microbes mineralize into available nutrients

Plant roots role in rhizosphere

• Plant roots are carbon pumps in the rhizosphere

• Plant rhizodeposition - fuels rhizosphere microbial activity (roots and carbon pumps)

  • Exudates and chemical signals

  • Mucilage

  • Root border/cap cells

  • C transfer to symbionts

  • Root turnover and cell lysis

  • Secretions

    • Purposeful compounds which plant signals to microbes to get nodules

  • Lysates (fluids with contents of cell)

    • Cell dies, contents are free

Stimulates microbes and predators

Mineralization definition

the overall process whereby organic materials are decomposed in simple inorganic products, like ammonium, nitrate, sulfate, or CO₂

Immobilization definition

the overall process whereby simple inorganic products, such as ammonium, nitrate, sulfate, or carbon dioxide (CO₂) are incorporated into organic forms during microbial uptake from soils

C:N ratios with net immobilization or mineralization

<15:1 - net mineralization

>35:1: net immobilization

Very dead SOM

• Stable SOM

• Humus - Ultimate stage in decomposition (historic view)

• Mineral-associated organic matter and physical separation from microbes (new view)

• Benefits:

  • Increases soil water holding capacity – through microporosity

  • Increases nutrient retention – surface areas hold electrical charges, that draw in and store cations

  • Stores/sequesters carbon

    • Less CO₂ release, since carbon is being sequestered

How is OM stored in soil

• Strong chemical bonds between organic matter and fine silt, clay, Fe^-, Al^-, Mn^- oxides, Ca²⁺

• Inside small aggregates (physically protected from decomposition)

• Humification: produces stable/complex substances such as humic materials that are resistant to biological decomposition

• Char produced by incomplete burning

  • Very recalcitrant, lasts for 100s of years

Labile SOM

• Lasts 1-50 yrs

• Lighter

• More complex

• Higher C to N than in stable SOM

Stable SOM

10-1000 yrs

Less complex

Heavier

More even C:N

What biome has highest SOM

• Boreal, tundra, and peatlands (northern hemispheres)

  • Living: not particularly active in cold areas (and also need oxygen)

  • Tundra, peatlands can be waterlogged - less oxygen

  • Anaerobic decomposition - slower

What texture of soils holds most OM

Finer textured soils can store more OM than coarse textured soils

• Greater surface area - more opportunity for SOM to attach

Feeding soil vs feeding plant

• Natural systems:

  • High SOM inputs

  • Little disturbance - few losses

  • C and nutrients cycled

  • Decomposing OM “feeds the soil”

  • Mineralized inorganic nutrients then “feed the plants”

• Onset of ag:

  • Lower SOM inputs

  • Intensive tillage

    • Accelerated OM mineralization and less recycling → net OM losses

    • OM losses through erosion

  • But still, feeding the soil and building fertility (manure, legume rotations, etc)

20th century ag, green revolution pros&cons

• Use of chemical fertilizers to feed high-yielding varieties

  • Shortcut: feeding plants directly with mineral nutrients

• Advantages

  • Chemical fertilizers more nutrient dense, (easy transport, more precise rates, and timing of application, increased yields)

• Disadvantages

  • We stopped feeding the soil (replaced nutrients, but not carbon), combined with intensive tillage → soil health degradation

Managing OM to build healthy soils

• Produce and cycle high amounts of biomass (crop type/use, residue; cover crop)

• Perennialize cropping systems to increase active growing ground

• Keep soil surface covered with living vegetation and/or residue

• Import OM inputs (manure, compost, biochar…)

• Reduce OM losses from decomposition and erosion

• The SOM Dilemma - shall we hoard it or use it

Primary limiting factors to soil biota activity

• Energy supply - phototrophs vs chemotrophs

• Source of cell carbon - autotrophs vs heterotrophs

All types of organisms (trophs)

• Light penetration for plants, algae

  • Phototrophs

• Substrate quality/availability for soil organisms (dirt)

  • Chemotrophs

• Carbon dioxide for plants

  • Autotrophs

• Organic carbon for most soil organisms

  • Heterotrophs

Soil food chain

• Primary producers (photosynthesizers)

• Primary consumers

  • Decomposers

  • Mutualists

  • Pathogens

• Secondary consumers

  • Shredders

    • Organisms which break up things into smaller pieces, increase surface area, colonize

  • Predators

  • Grazers

    • Bacteria along surface of a root: protozoa will “graze” it

• Higher level consumers

  • Predators

What makes soil biota unique vs marine, lake biota?

• More biodiversity

• Slower growing organisms

• Novel lifeforms

  • Significant percentage in unknown organisms

Soil bacteria roles

• Decomposing OM

• Releasing nutrients

  • Only after their own needs are met

• Retaining nutrients in biomass

• Controlling pathogens

  • Also are pathogens

• Solubilizing phosphorus

  • Phosphorus tends to get stuck on soil exchange complex

  • Binds to things like clay: enzymes can release phosphorus 

• Aggregating soil

  • Mineral-associated organic matter MAOM

• Forming soil organo-mineral associations

Base of the food web

Bacteria, including actinomycetes, form the base of the soil food web
Diverse nutrient requirements and temperature ranges

• Population specialists

• Actinomycetes

  • Filamentous growth

  • Earthy smell - geosmins, good sign

Nitrogen cycle - players and roles

Mediated by microbes
SOM also has key role

• Original source of nitrogen is N₂ from the atmosphere

• Vast majority (>90%) of N is bound in soil organic matter

• Most transformations in the N cycle are mediated by microbes: nitrogen fixation, mineralization, nitrification, denitrification

• To predict state and fate of N we need to understand these microbes

Nitrogen cycle

Nitrogen fixation → mineralization to NH₄⁺ (ammonium, positive, sticks around) → nitrification (nitrate, NO₃^-, leaches easily) → denitrification (N₂ + N₂O)

Composting info

Requires microbial action

• Thermogenic compost

  • Windrow system: organic residues, microbes and mechanical turning

• Vermicompost

  • Continuous flow through reactor system: OM, microbes, and epigeic earthworms (Eisenia fetida)

    • Give plenty of carbon to balance nitrogen

Approaches to bacterial control

• Inoculations

  • Nitrogen fixing bacteria

  • P solubilizing microbes 

  • Hormones analogues

  • Microbial soups (PGPR)

  • Compost teas

• Cultural control

  • Add OM

  • Reduce toxins

  • Keep plants in system

  • Oxygenate the soil

  • Improve drainage

  • Lower bulk density

Fungi roles

• Decomposing OM

• Mobilizing P 

• Controlling pathogens

• Promoting plant growth

• Controlling insects

• Aggregating and stabilizing soil

Fungi can grow on crappy substrates lacking in nitrogen 

Arbuscular mycorrhizal fungi (AMF, used to be VAM)

• Arbuscules - arbor, tree-like structure for exchange 

• Membrane supports integrity

• Obligate, cannot complete life cycle without plants

  • Have to use spores to colonize roots

  • Fallow bad for AMF

• Colonize most crops

Fungi management approaches

• Inoculants 

  • EMF and AMF

  • Trichoderma

  • Metarhizium

  • Beauvaria

• Cultural control

  • Reduce tillage

  • Add higher C:N OM

    • Fungi do better on low N material

  • Reduce use of toxins

  • No bare fallows

C:N ratios of organisms

N mineralization at <20:1

• Used to understand the ratios of C and N required to satisfy metabolic needs

  • Bacteria 3-5:1

  • Fungi 10-15:1

  • Protozoa 10:1

Earthworm activity

Turn over leaf litter too fast, expose bare soil

• In agricultural systems:

  • Stimulate microbial activity

  • Mix and aggregate soil

  • Increase water infiltration and water holding capacity

  • Provide channels for roots

  • Shred and bury plant residues, increasing SOM

Earthworms are easily harmed - cultural controls to encourage them

• Reducing tillage

• Reducing use of chemicals, toxins

• Increase OM inputs

Protists

“Turn over” microbial biomass

• Need water

• Ciliates (use cilia for locomotion, eating), flagellates, naked and testate (test = amoeba house) amoebae

Functional roles":

• Primary consumers of bacteria in soil

  • Regulate population size and composition

  • Accelerate turnover of soil biomass/OM

  • Maintain plant available N

    • Bacteria very nitrogen rich (5:1), versus protozoa which is only 10:1

  • Prevent pathogen establishment

• Food source for fungi, nematode, other

• Can cause disease as animal parasites

Soil nematode roles

• Abundant, small, water-dependent

• Functional roles

  • Feeding on bacteria, fungi, protozoa

  • Controlling bacterial numbers and population structure

  • Releasing large amounts of N while feeding and upon death

    • Because they eat bacteria, and get more N than they need

  • Helping to maintain plant available N

  • Selective feeding influences

    • Soil structure

    • C utilization rates

    • Types of substrates present in soil

    • Plant and animal parasites

Nematode feeding

• Diverse range of feeding strategies

  • Plant parasites

  • Bacterial feeders

  • Fungal feeders

  • Predators

  • Omnivores

• Plant parasitic nematodes are a problem, but all the others are very important

Managing nematode populations

• Inoculants

  • Enthomopathogens

• Biocontrol

  • Bacteria, viruses, microsporidia

• Cultural control

  • Encourage diverse saprophytic food web

What is required for mineral nutrient release?

A complex food web

Functional roles of soil fauna

• Shred OM (mites, springtails (Collombela)

• Stimulate microbial activity

• Mix microbes with their food

• Mineralize plant nutrients

• Enhance soil aggregation

• Burrow

• Control pests

• May be pests

Shredder examples

• Sow bugs, dung beetles, mites, Collombela (springtails)

Herbivores

• Mole cricket

• Cabbage looper

• Locust

• White fly

Soil predators - crop pest control examples

• Wolf spider

• Harvester ants

• Pseudoscorpions

• Lady beetle

Drivers of microbial activity (biological, chemical, physical)

• Biological factors

  • Competition

  • Predation

  • Allelopathy

• Chemical factors

  • pH

  • Moisture

  • Oxygen

    • Oxygen is human’s ultimate electron acceptor, but not the case for some anaerobic bacteria

  • Carbon dioxide

    • Having an alternative chemistry (diff ultimate electron acceptor) very beneficial in the soil

  • Inorganic nutrients

    • More acidic - heavy metals more soluble, only tolerated by some organisms

• Physical factors

  • Texture

  • Porosity

    • Most important - give organisms a home

  • Compaction

  • Bulk density

  • Temperature

Key biological processes in healthy soils

• OM decomposition/accumulation

• Nutrient transformations and availability

  • Organic fertilizer - feed soil

  • Synthetic fertilizer - feed plants, reducing SOM

    • With excess of N without carbon like in synthetic fertilizer, C:N ratio is skewed; organisms will take C in faster given so much N, making the ratio worse

• Disease, disease suppression

• Immobilization of toxins

• Well-supported microbial community of beneficials producing plant growth promoting compounds

Why are roots a good indicator of soil health

Have clear symptoms to following problems:

• Poor drainage

• Poor nutrient availability

• Severe compaction

• Pathogen infections

  • Rhizoctonia

  • Pythium

  • Root-knot nematodes

6 Macronutrients and common forms

N - ammonium, nitrate

P - H₂PO₄^-, HPO₄^-2

K - K⁺

S - SO₄^-2

Mg - Mg²⁺

Ca - Ca²⁺