Soil exam #3

pH

A measure of acidity or alkalinity of soils and other materials.

Macro-organisms

Soil organisms greater than 2 mm in size, including worms and termites.

Meso-organisms

Soil organisms ranging from 0.1 to 2 mm in size, such as springtails and mites.

Micro-organisms

Soil organisms less than 0.1 mm in size, including tardigrades, nematodes, fungi, bacteria, and archaea.

Chemoheterotrophs

Organisms that obtain energy from organic compounds carbon sources, and engage in biochemical oxidization.

Photoautotrophs

Organisms that use solar radiation to convert carbon dioxide into organic carbon. Typically includes plant ROOTS, algae, cyanobacteria.

Primary consumers

Herbivores(plants live), detrivores(dead plants and microbes on them) and saprotrophs (microorganisms that consume detritus corpses and feces

Detrivores

Organisms that feed on the remains of dead plants and microbes.

Saprotrophs

Microorganisms that consume detritus, corpses, and feces.

Secondary consumers

Carnivores that eat other animals, such as microbivorous that feed on microbes.

Soil organic matter (SOM)

Contains elements in living biomass, primarily carbon, nitrogen, and other nutrients. (58% carbon by mass, 1-6% nitrogen)

Turnover rate

The proportion of a pool that leaves during a given period of time. (turnover rate = output/pool)

Residence time

The average length of time that a molecule remains in a specific pool. (Residence time= pool/output)

Carbon cycle

The ongoing process of carbon movement between land, oceans, and the atmosphere.

Humification

The process by which organic matter decomposes into stable organic substances in soil.

Mineralization

The process by which organic nitrogen is converted into plant-available forms, such as NH4+.

Nitrification

The process by which ammonium (NH4+) is oxidized to nitrate (NO3-) by nitrifying bacteria.

Denitrification

The process by which nitrate is converted into gaseous nitrogen forms, reducing nitrogen in the soil.

Nitrogen fixation

The conversion of atmospheric nitrogen (N2) into organic compounds by certain bacteria.

Haber-Bosch process

An industrial process for synthesizing ammonia from nitrogen and hydrogen, significant for agriculture.

Potassium (K)

An essential nutrient for plant growth, involved in various cellular processes.

Eutrophication

The process by which excessive nutrients, primarily nitrogen and phosphorus, enter aquatic systems, leading to oxygen depletion.

Legacy P

Phosphorus that accumulates in soil beyond plant needs, which can slowly release into waterways.

Organic N inputs

Nitrogen inputs from organic sources, considered less mobile than mineral nitrogen inputs.

Volatilization

The process by which ammonium (NH4+) loses a hydrogen to become ammonia (NH3) gas.

N balance

The difference between nitrogen inputs and outputs in a given system, indicating nutrient management effectiveness.

Mycorrhizal associations

Symbiotic relationships between fungi and plant roots that enhance phosphorus uptake.

N leaching

The process by which nitrogen from the soil is moved away through soil layers , typically transported through rainfall and groundwater.

Carbon outputs

The loss of carbon from soil pools due to processes like respiration, harvesting, and erosion.

Chemoautotropphs

Use carbon dioxide and carbonate from INORGANIC sources as energy source. Ammonia oxidizers and sulfur oxidizers.

Why is SOM persistent

Carbon is deposited by plant matter, some gets immedately decomposed, some lasts for hundreds of years

Evolving views of SOM

Fast vs slow cycling pools

faster cycling SOM pools

POM and POC

Slow cycling

MAOM and MAOC

Formation of Particulate organic matter (POM)

A root or shoot enters soil (plant death or turnover) → +CO2 expelled → decomposer activity reduces size and mass of root, and alters chemical composition → CO2 expelled, remaining is >2mm> → Remaining fragments of root become POM

Formation of MAOM (mineral associated organic matter)

A root deposits carbon such as through exudation → plant carbon is directly adsorbed to minerals or processed by microbes → organic matter associated with minerals become MAOM

carbon inputs

Aboveground litter, animal waste, organic ammendements, roots, root exudation

Carbon outputs

Respired C (CO2) Harvest C (agricultural) Erosion, Leaching of dissolved organic C4

Protection mechanisms of SOM

Limit microbial access or activity in order to preserve the som

Protection of SOM for longer residence time are occluded in

Aggregates

SOM absorbed into —— surface is less vulnerable to microbial decomposition than a counterpark moelcule that is in a soil solution

Mineral surfaces, AKA (MAOM

Low O2 does what to microbial activity

induces anaerobic conditions, slowing down activity (happens when wet)

Low temp limits microbial activity

Reduces rates of ability to function

Low pH limits microbial function

More acidic solutions preserve for longer (like pickles)

high C:N as a limitation of microbial activity

Ratio of carbon atoms per one nitrogen atom, as it gets higher the C number gets it corresponds to the higher difficulty in decomposing organic material

Historical view vs new view of litter inputs

Textures role in SOM

Total mass of silt+clay but also its activity increaase MAOC

Arid soils and Carbon correlation

Arid soils dont have water tp supply plant matter to supply carbon to the soil, no output if no input

Soil heath =

SOC

SOC is gained or lost under conversion to agriculture and SOC regeneration

Lost,

Why might not till plots have greater difference between SOC concentration between different parts of topsoil?

Tilled system its being incorporated into the soil, no till the plant matter status on surface. No tilled surface leaves plant matter on surface horizons

ways of Measuring a SOC pool

1. Concentration - mass SOC /mass soil
   2. Stock = mass SOC / area and depth of soil 

Why does bulk density affect measurement of SOC sock

Sampling two soils of the same depth but different bulk densitys will capture different masses of soil. Denser soil will have greater stock in top 30cm even if concentration is the same.

SOM fractionation

Causing disruption to a soil sample to measure the SOC and POC by separating the soil into different fractions based on chemical or physical processes

Phtotosynthesis -RuBisCo - requires nitrogen

An enzyme that catalyzese the conversion of CO3 to organic carbon

Nitrogen limits plant growth when there isnt enough

more nitrogen, more growth, limitation stronger in temperate soils

how to plants acces plant avaible nitrogen (usually in mieneral) form

Plants get nitrogen from soil via root uptake

Nitrogen cycle

The process through which nitrogen is converted between its various chemical forms, moving from the atmosphere into the soil and living organisms before returning to the atmosphere.

Two forms on N in soil

Ammonium (NH4) reduces electron rich N,Nitrate (NO3) oxidized or electron poor N species

Nitrification

NH4 will be oxidized to N03 for energy by microbe known as nitrifies (CHEMOAUTROTROPHS) using O2 as a terminal electron acceptor

Immobilization: microbial uptake of mineral N

IMportant for controlling N availablity to plants and preventing nitrogen loss by incorporating it into their biomass. This process involves the conversion of nitrogen from inorganic forms into organic forms by microorganisms, ultimately affecting the nitrogen balance in the ecosystem.

NH4 fication by soil colloids

adsorptiob of ammonium ions by the mineral or organic portion of the soil in a manner that they are raltively unexchangable by usual methods of cation exchange which helps retain cations.

Colloids can HIDE NH4 in this way

N LEACHING LOSS

Transport o fdissolved N out of soils and into coastal water - predominately NO3 due to its inability to be held in cation exchange but may also incldue NH4

Occurs when mineral N pools in soil > plant uptake + precipitation > evap

eutrophication

What is a highly oxidized species of N good for

nitrates are most accessable and usable form of nitrogen plant growth and industrial processes,

Denitrification

NO3- ions are converted gaseous forms of nitrogen by denitrifies. happens in the ABSENCE OF OXYGEN

Biological Nitrogen fixation (BNF)

The pathway for N2 to enter terrestrial cycle, via nitrogen fixing of bacgteria (rhizobia) and host legume. Impreded by low pH, low P Ca and K avaiblity

Haber - Bosch process

Converts atmospheric N2 to ammonia NH3 using hydrogen gas under high heat and pressure. Critical source of N in fertilizers

Nitrogen is the most abundant gas in the atmosphere in the primary form of

N2

Why is nitrogen an important element for life

because it is essential for the creation of protiens

The number of covalent bonds that connect two N atoms in a molecule of N2

Three

Is Oxygen the only terminal electron acceptor used my earthly life forms

NO

is Phosphorous as a gas; analogose for N fixation, P fixation by plant microbe symbioses, is essential for P cycling

false is not a gas but an essential nutrient for plants, involved in energy transfer and photosynthesis.

A cover crop by growing during times that woudl otherwise fallow

Can reduce nitrate leaching, can reduce rates of soil erosion, and promote BNF

Plant avaible nitrogen in soil refers to

Mineral N as both cation NH4 and anion NO3

Is The majority of soil N is held in plant avaible forms

False

Nitrification refers to

The oxidization of ammonium to nitrate

Processes in soil nitrogen transformations care carried out primatily by heterotrophic microbes include

SOM mineralization and denitrification

Leaching of mobile N from agricultural fields

Contributes to eutrophication of riverine and coastal waters

Denitrification

Is a formant microbial transformation of N when soils are wet (and therefore anaerobic)

Denitrification

Returns N to the terrestrial N cycle to the atmosphere

Pathways through which atmospheric N2 can enter soil and plant systems include

Biological nitrogen fixation adn haber bosch process

Crop responses to mineral N fertilizer input

Plateu once N becomes non- limiting

Sidedress N applications

Align timing of N application with timing of plant N uptake

The two pools that make up most soil organic matter currenlty recognized as

Particlate organic matter and mineral-associated organic matter

As a part of the global carbon cycle, soil organic matetr is imporant becaue

It comprises more carbon than what is held in the atmosphere and terrestrial vegetation combines

best descrption of pools and turnover of organic carbon

smalelr faster cycling pools and larger slower cycling pools

Mineral associated organ carbon

Is more persistent in soil than particulate organic carbon (POC)

Particulate organic carbon

Various forces can limit microbial respiration and ability to encounter organic C compounds in soil

The pool size of SOC is determined by

the historical balance of C inputs and C outputs

C:N ratio of litter

corresponds to its decomposition rate, with lower C:N litters decomposing more rapidly

n order to calculate stock of SOC (Mg, C/hA youll need)

concentration of SOC, bulk density and sampling depth

is fractionating SOC into POC and MAOC is the only approach currently or historically used to study SOC dynamics

No, methods include physical chemical and biological techniques

using practices that protect or increase SOC stoks in soil can aid in

climate change mitigation, improving soil health and enhancing agricultural productivity.

Phosphorous is a critical element of life because

It is part of nuceleic acids and lipids

does P in soil exists in organic and inorganic forms

yes

The phosphorus cycle differs from nitrogen cycle becuase

P cycle doesnt have a gaseous pool

If you add inorganic phsophorus fertilizer to soil you might expect

A significant proportion is fixed into inorganic forms, depending on Fe and Al oxide avaiblaity

inputs of phosphorous to soil with no human altercation include

dust