soils science test 3

CO2 --> H2CO3 carbonic acid--> HCO3 and H+

Organic matter accumulation

Oxidation reactions

Plant uptake of cations

controls soil chemistry (nutrient availability and toxicity)

soil biology (microbial activity and diversity)

Soil physics (determines aggregate stability, Al=good aggre. Na =bad aggre)

• raised by reduction rxn
• lowered by oxidation rxn

the ability of soil to resist change in pH. It is increased in soils with high CEC

CO2 reacts with water to form H2CO3 which breaks down to HCO3 and H+

CO2 + H20--> H2CO3 --> HCO3 + H+

at equalibrium at pH 5.6

organic material forms soluable complexes with non acid nutrient cations (CA, MG, ect) increasing their loss by leaching

Organic acids form H+ ion

strong acids are produced which increase soil acidity

plants take up neg charged anion or exude a positive charge as a different cation. when they take up more Cation than anions , plants usually exude H+ ions into the soil solution to retain charge balance in the soil

• leaching
• Al hydrolysis -

Al 3+ splits water molecule into H+ and O- ions. Al combines with the OH-, leaving the H+ to lower the pH of the soil solution. Can create 3 H+ ions in solution. Then these H+ join together forming large polymers with many + charges. Once bound to the colliods negative surface, polymers don't exchange and masks potential cation exchange capacity

Leaching removes HCO3, CO2 which produce OH

They accumulate Al and H

• Carbonates & bicarbonates
• Reduction reactions of N S Fe
• Weathering reactions to certain salts

• -CO3 2- (carbonate) from Ca minerals like calcite
• -HCO3 (bicarbonate) and from carbonic acids

• React with H20 and OH- ions
• CaCO3== Ca +CO3
• CO3 +H20 == HCO3 + OH-
• HCO3 +H20 == H2CO3 + OH-
• H2CO3 == H20 + CO2 gas into air

Weathering creates calcarous (calcite laden) and sodic (sodium -carbonate laden) horizons

Calcite and carbonates engage in reactions w/ H20 and OH- to create more OH-

• Pool of :
• Active Acidity
• Exchangeable Acidity
• Residual Acidity

• H+ in soil solution
• -smallest of the pools
• -determines the solubility of many substances
• - environment around plant roots
• -easy to adjust or fix pH

exchangeable Al and H on te colloid surface

Once the Al3+ is released through CEC and the solution hydrolyzes H20, H+ is released into the soil solution lowering pH

• to nuetralize exchangeable acidity it takes 100 times more liming material than active acidity pool
• Smectites> vermiculite> kaolinite

H, Al, and AlOH molecules that are bound in inexchangeable form

-once the pH increases the bound H dissociates and the Al ions are released. This Al can be hydrolysed and will add more H+ to the soil solution so the exchange rate can be 1000-100000 times greater than active acidity

Once the soil solution is nuetralized, it is relensihed with H+ ions from the exhangeable pool

Soils high in clay and OM are highly buffered

• Important because:
• ensures some stability in pH , preventing drastic fluctuations in pH

buffering dictates how much liming ammendments toadd

• -Fungi are still alive
• -bacteria and actinomycetes are beginning to die off
• -Al toxicity a problem
• -Fe , Mn, Zn, Cu is radily available
• -N, K, S, Ca, Mg, Mo not easily available
• -pH < 5 bacteria in nitrogen fixation die off so N is unavailable

• -fungi living
• -bacteria and actinomycetes are alive
• -N, K, S, Mg, Ca, Mo are available
• -P Cu, Zn is not available
• - B deficiancy is a problem
• -as pH increases micronutrient solubility rate decreases

most commonly a problem in serverly acid soils <5.2

Al3+, Al(OH)2+, Al(OH)-

Soluable Al

Al is strongly attracted to OM which will tie up soluable Al in the soil solution.

al damages cell membranes and restricts cell wall expansion

Al interfers with P metabolism

levels can't be tested by leaf sample cuz only in roots

• Al saturation
• Al >15% problem soil

OM and liming to 5.5

Al bound with OM

crinkling and cupping of leaves

intervenal patches of chlorotic tissue

Lime to pH above 6.0

manage irrigation

aerate soil

liming materials react with CO2 and H20and create bicarbonate

the salt ions of the liming material replace Al and H+ ions on colloid surface which lowers the % acid saturation on colloid surface raising the pH

• Liming material ==ions + carbonate
• carbonate + H20 == bicarbonate + OH
• bicarbonate +H20==H2CO3 + OH
• H2CO3== H20 + CO2 gas

Al will react with some of the OH- ions forming Al(OH) which is insoluable and no longer dangerous to plants

the process that releases elements from organic compounds to inorganic compounds through microbial assimilation.

NH4+ --> NO2--> NO3--> N2 gas

Its the last step in decomposition.

the conversion of inorganic compounds to organic compounds through microbial assimilation

The microbially mediated conversion of NH4+ to NO2- to NO3- in aerobic conditions

Microbially mediated conversion of NO3- to N2 gas in anaerobic conditions

Can happen in aerobic conditions in the micropores where water is trapped

1. High pH in water or soils solution leads to NH3 producation

2. Urea especially volnerable, bury it

anaerobic ammonium oxidation

bacteria at the aerobic/anaerobic interface converting NH4+ to NO2 to N2

skips from NH4+ to N2 through bacterial assimilation

• Plants
• OM
• microbs
• ECE (NH3+)
• ACE
• in soil solution
• in atmosphere

entrapment of NH4+ between the interlayer spaces of vermiculite

• nitrification aerobic
• denitrification in anaerobic

• BNF
• plant and animal residues
• NH4+ (acidify)

• KNO3
• CaNO3

• most carbon in lithosphere
• Plants fix C in tissue and into soil as humus
• decomposition release C
• tilling mining disturbs protect surface soil and exposes microbs to more air which speeds demposition releasing more CO2 than without tilling

microbially mediated breakdown of complex molecules into more simple components

some components are mineralized by microbs to make new compounds

• Energy
• Water
• CO2
• humus

bacteria fungi and earthworms

up

• 1) Sugars, Starch Simple Proteins
• 2)Crude Protein
• 3) Hemicellulose
• 4) Cellulose
• 5)Fats and waxes
• 6) Lignins and phenolic compounds

• Molecular structure
• Fragmentation
• Microbial metabolism
• Temp

amorphous and colloidial mixture of 5 ring carbon substances

complex molecules with high molecular weight and resistant to microbial degradation

microbially modified plant compounds with simple structure

• dark
• improves aggrigation
• improves water retention

• Increases CEC (humus=CEC 200)
• increases buffering capacity
• Detoxifies Al
• Increases microbs through chelates (organic compounds) with humic substances

increases soluability of micronutrients

increase bioiversity and microbially mediates reactions like immobilization and mineralization

• Active
• Slow
• Passive

rapid turn over (1-2 yrs)

• -Non-humic substances
• -Nutrient source for NPS
• -Easily depleted through tillage
• -important source of aggregation through carbohydates in OM

• intermediate stability (decades)
• -source of longterm NPS

complez humic substances (centuries)

Temp- high temp=faster decomp

Moisture- more water more veg more litter, also anarobic slows decomp

Veg- litter

Soil texture-high clay and silt usually rich in OM cuz it produces more biomass.

Tillage- destroys microbs slows decomp, also carbon is explosed weather

HABITAT

soil health

ability to continue to perform functions in a wide variety of environments

• plants
• algae
• lichens
• bacteria

bacteria easily

fungi more complex

40%: 60%

converts N2 to reactive N

• -symbiosis=mutual
• -obligate= mediated by prokaryate organisms
• -associate=actinomycetes

N2 + 8H +8e --nitrogenese-->2NH3 + H2

is the key enzyme in BNF

it protects the nitrogenese from O2

Actinomycetes that fix N on nonleguminus plants

forest soils

N fixation exceeds leguminous action

anabeana cyanobacteria

P and immobile nutrients

B Cu Fe Mg Zn Mo Cl Cobalt Nickle

N P K Mg

• yellowing due to loss of chlorophyll
• Uniform and interveinal

death of plant tissue

accumulation of anthocynan

yellowing on older leaves, stunting reduced yeilds

• purple or redish color
• necrotic spots on older leaves
• overall stunting

• chlorosis along leaf margins
• weak stems
• small fruits

interveinal chlorosis on older leaves

• younger leaves necrotic
• poor growth w/ delayed maturity