Soils exam 3

What is aeration and what are the benefits of it

mvoement of gas through the soil is the defintion

it can be good for maintaining high macroporosity and permeability

it can help to balance out H2O content

it can help plants roots by allowing them easier access to O2

can help forming aggregates

can help maintain a good tilth (keeps soil friable/easy to crumble)

how much water is okay for the soil

60% or less

What does it mean if the soil is water logged, and what type of plants thrive here and what plants die here

when 80% of pores are filled with H2O

this is often seen in wetlands, which have plants adapted to this (hydrophytes)

geophytes are plants that do well in aerated soils, so they die here

haleophytes are adapted to changing conditions

WHere are wetlands located and what problem are we seeing with them

THey are lcoatred all over the world except for antarcica, but antarctica does have permafrost (ground frozen for 2 years)

global warming has been unfreezing these wetlands, releasing them and the methane gas they had in them

what is ventilation and what are the two ways it is done

defintion of ventialtion is the exchange og gas, can be thorugh soil

1) Mass flow: there is an irrigation vent, water goes into vent, and the water pushed the gas up. water displaces gas. This occurs mostly at the surface

2) Diffusion: gas moves from high to low concentration. this is the most common way ventialtion happens. O2 and CO2 are the most commonly moved gases

Redox potential

the tendency/potential for electrons to mvoe from one substance to another in redox reactions

in redox reactionsm oxidation si when an electrion is lost and reduction is when an electron is gained

oxic soil vs anoxic soil

oxic soil has soil that has been oxidized (has oxygen) and is aerated

anoxic soil has soil that is poorly aerated (low O2 and high water content)

• the standard is that a soil must be over 80% water content for it to be anoxic

  • because there is so much water and so little oxygen, anoxic soil can easily be toxic for plants

What are the factors that affect soil aeration and Eh (redox potential)

1) drainage of excess water

• more drainage, more aeration and lower Eh (More aeration means lower Eh/redox potential. more water means more Eh/redox potential because water can carry electrons easier)

2) Rate of respiration in microbes and plants

• more respiration equates to more gas exchange

3) Soil hetergentity

• Tillage: breaks up soil shor term, forms aggregates and increases pore space (increase of pore space from tillage results in less Eh)

• Pore size: more aeration means smaller Eh

  • plant roots: plants increase pore space size and spore space in general,a nd they also take up water.

Ecological effects of soil aeration

On OM Decomp:

• higher temperature means means higher decomposition, and this means higher aeration

Redox of elements

• more aeration means more oxidation occurs

• N: not fully decomposed, it is toxic. ust be in oxidized form to be sued by plants

• Phos: same way, must be oxidized

• Pottassium: also must be oxidizes.

• - soil must be aerated to make this oxidation happen

Greenhouse gases:

• when reduced CO2 into soil

• when oxidized, methane in soil

Higher plants

• more aeration leasds to more plant growth and more nutrient and water uptake

How does aeration relate to soils and plant management?

field aeration is enhanced by

• maintaining soil aggregation, (more aggregation emans more eration)

• surface and subsurface draining, (more drainage means less water, more aeration)

  • engaging vertically oriented biopores (engaging pores means more aeration)

Processes affected by soil temperature

Vernalization: plants require a cold spell to promote flowering, vernalization is this process

• 0-5C (cryophilic)

solarization: tarp thing to trap heat. 57-60C(meso). temperature so high that it may kill pests and stuff

optimium: ideal reange for [plants to germination, roots to grow, faster microbial processes, etc (25-30C - meso)

hard seed germination: soaking or whatever done at 75-80C

Two processes that are caused by soil temperature

1) Freeze Thaw

• H2O in soil expands when its frozen, making water table go up

• H2O in soil contracts when thawing, making water table go down

• forst heaving: rocks aand maybe soil are pushed up

2) Heating via fire

• one fo the mose far reaching disturbances in nature

• above ground forests urn obvs

• below ground, OM distilled (above 125C. this distilled OM may make the soil hydrophobic

- chaparrel: small and stubbly bush

Absorption and loss of solar energy terms and influences

albedo: amount reflected back/not absorbed

aspect: facing toward or away from sun

rain: seasonal influence

soil cover: layer of vegetation that helps to absorb and redistribute heat into soil (makes soil cooler and redistruvtes heat)

Thermal Conductivity (k)

this is defined at the rate at which heat moves through soil

this is affected by bulk desntiy (high bulk density lowers pore space, making heat move slower)

• loose and dry: low K (low thermal conductivity)

• compact and dry: medium k (compact enough but no water to carry heat)

  • compact and wet: high k

temperatures of atmosphere vs soil

hottest temp of atmosphere during day is 12-2

soil is 4pm, so there is a 2-4 hour lag

• most fluxuation in soil temp happens above 80

How do we control soil temperature

mulch from conservation tillage

• more concerns in cool climate for temp control than in wrmer climates. warm climates find mulches advantagerous

palstic mulches extend growing season

Decomposition in soils

microbes like upper mesophyll, and every 10C increases microbial activity by 2-3x

how fast they are depends on soil type

Soil types based on rapid to slow decomposition

sugars, starches, simple proteins are the fastest

crude proteins

hemicellulose

cellulose

fats and waxes

lignins and phenolic compounds are the slowest

immobilization is

high C:N ratio (Lignins and phenolic compounds) that are not able to be used by plants because hold on the N in soil

mienralization is

low C:N ratio (Lignin/phenolic compounds) - makes organic materals inorganic, making them available for plant use

factors affecting rate of decomposition and mineralization

environmental conditions

• good aeration increases decomposition rate, so does warmer temps

CN ratio of organic materials (quality depending on L:P content) added for food for microbes

• should be C:N is 20-30:1

• shredded wood better than leaf litter

L:P content

• should be over 20% Lignin, should be over 3% Polyphenol

Two types of compost

OM matter decomposing above soil

vermicomposting: food and organic matter with worms, vermicast being the final product

thermophilic is using thermophilic microbes to compost. pathogens can also be killed

K strategists vs R strategists

K: slow and steady, works to make new humus

R strategist: rapid, works to make biomass

both work together for C digestion

SOM

encompasses all OM in soil

• living biomass like intact aimal and plant tissue

• detritus, which is dead plant residuee

• humus, which is nonliving, nontissue

Humus

nonliving tissue that is very stable

contains humic (polymeres that are from decomposed material, acids) 60-80% humus

also contains nonhumic substances which are not polymeres, meaning that are easily degraded like AA, fats, sugars, etc. 20-30% humus

How are clay-humus combos good

help with water retention, nutritient retention, and improving soil structure