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ENVS 200 > Exam #3 > Flashcards

Exam #3 Flashcards

1
Q

what are the three domains of life?

A

-eukaryota
-bacteria
-archaea

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2
Q

generally, what type of organisms are eukaryotes?

A

fungi, protists, plants, and animals (membrane bound organelles with nucleus)

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3
Q

what type of organisms are prokaryotes?

A

archaea and bacteria (don’t have membrane-bound organelles)

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4
Q

describe the kingdom protista

A

very diverse eukaryotes that are a part of an “other” category that aren’t plants, animals or fungi; some can move and photosynthesize, some form colonies such as slime molds and kelp.

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5
Q

describe the soil trophic levels

A

primary producers –> primary consumers (herbivores) –> secondary consumers –> tertiary consumers
decomposers: consume all dead organic matter and release plant nutrients (all trophic levels)
primary decomposers:
>detritivores: eat dead or digested plant debris
>saphrophytes: eat dead or digested plant and animal debris (responsible for most decomposition)

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6
Q

what are the different size classes of soil organisms?

A
  1. macro-organisms (>2 mm)
  2. meso-organisms (0.1-2mm)
  3. micro-organisms (<0.1mm)
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7
Q

what organisms are considered macro-organisms?

A

-plant roots
-burrowing animals
-earthworms
-ants and termites

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8
Q

__________ _______ are macro-organisms which are ____-____ of plant mass. they are ___-______ um in diameter

A

plant roots
30-50%
10-400

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9
Q

how do plant roots enrich SOM?

A

roots enrich SOM with:
exudates: dissolved organic compounds exuded by roots
ex: acids, sugars, mucigel, shedded cells, dead roots
-root respiration (1/3 to 1/2 of soil CO2)
-create biopores

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10
Q

what is the rhizosphere? what does the rhizosphere has more of compared to non-rhizosphere soil?

A

zone most affected by roots (2-3cm of roots)
the soil in the rhizosphere has
-more SOM (more sugars)
-more chelates –> increased complexation
-lower nutrients (more acids)
-lower O2, more CO2 (due to more respiration)
-lower aeration
(compared to non-rhizosphere soils)

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11
Q

describe burrowing animals that contribute to macro-organisms and how they impact soils

A

diverse species and trophic levels: mammals, reptiles, insects, and amphibians (multiple ecological roles: detritivores, predators, and herbivores)
soil impacts: translocate and mix soil, create networks of biopores, and aerate soils

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12
Q

ants and termites have multiple ecological roles (herbivores, predators and detritivores), how do their nests impact soils?

A

-improved soil aeration
-increased infiltration
-modify soil pH
-local enrichment of nutrients
(habitat for ants: temperate, for termites: hot, dry)

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13
Q

what habitat are earthworms (Annelida) found in? what are their functions?

A

cool, moist aerated soil with neutral pH; most abundant animal microorganism in moist humid regions.
functions: mix soil particles and nutrients, improve soil structure (increase aggregation)

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14
Q

what are different types of meso-organisms?

A

rotifers
springtails and mites
tardigrades (“water bears”)
nematodes (unsegmented worms found in almost all soils)
protozoa

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15
Q

describe protozoa and where you might find them

A

mobile, unicellular eukaryotes of the kingdom protista (some photosynthesize). they are predators who eat bacteria, 4-250 um in size. habitat: prefer moist, aerated surface soils

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16
Q

what 4 things do all organisms need to survive?

A

-electron acceptor (oxidizing agent)
-carbon source
-water
-mineral nutrients

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17
Q

where do autotrophs get their carbon/energy from?

A

C from inorganic compounds (CO2 or CO3 2-)

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18
Q

where do heterotrophs get their carbon/energy from?

A

C from organic compounds (with C-C and C-H bonds)

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19
Q

where do chemotrophs get their energy from?

A

energy (e-) from chemicals

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20
Q

where do phototrophs get their energy from?

A

energy (e-) from light

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21
Q

what are chemoheterotrophs?

A

energy source from biochemical oxidation and carbon source from organic materials (all fungi, all animals, most bacteria)

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22
Q

what are chemoautotrophs?

A

energy source from biochemical oxidation and carbon source from CO2 (deep ocean microbes, N + S oxidizers)

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23
Q

what are photoheterotrophs?

A

energy source from sunlight and carbon source from organic materials (some bacteria, algae and protists)

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24
Q

what are photoautotrophs?

A

energy source from sunlight and carbon source from inorganic CO2 (algae, cyanobacteria, and higher plants)

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25
Q

what 8 environmental conditions affect soil microbial growth and activity?

A
  1. organic substrates
  2. nutrient substrates
  3. oxygen/redox status
  4. temperature and sunlight
  5. moisture
  6. pH
  7. salinity
  8. toxins
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26
Q

what is the Baas-Becking Hypothesis?

A

everything is everywhere but the environment selects

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27
Q

most soil microbes prefer when soil water content is near ________ __________

A

field capacity (too dry = microbes can’t get water or solutes)

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28
Q

how does soil aeration affect soil microbes?

A

good aeration –> aerobic microbes dominate = faster growth and decomposition
too much water (saturated) –> low aeration (low O2)
–> anaerobic respiration = slower growth and decomposition
(alternative electron acceptors = NO3-, SO4 2-, Fe3+, and Mn4+)

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29
Q

what is the ideal pH and temperature range for soil microbes?

A

optimal pH is near 7 (fungi tolerate acidic conditions well)
temperature:
-thermophiles (55-65 degrees C)
-mesophiles (25-37 degrees C)
-psychrophiles (15-20 degrees C)

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30
Q

simple substrates are decomposed _____ _______ than complex substrates, like cellulose and lignin.
_________ decompose cellulose and lignin more effectively than __________

A

more rapidly
fungi
bacteria

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31
Q

what are algae, what effect do algae have on soils, and what habitat are they found in?

A

photoautotrophs (protista and plantae, 2-20 um)
soils effects: add OM and microbiotic crusts
habitat: need a fairly moist environment and mostly at soil surface (for light)

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32
Q

what are slime molds? where are they found in the soil?

A

protists (eukaryotes): amoeba-like cells that spend most of the time as single cells; they form colonies.
-colonies form networks and possibly also think
ecology: feed on bacteria and can congregate together into 0.1mm mounds
habitat: live in O and upper A horizons

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33
Q

what are fungi? what impact does fungi have on soils?

A

eukaryotes; most are filamentous (hyphae = root-like filaments) (mycelia = woven hyphae) can be uni- or multi- cellular. (yeasts, molds, mushrooms)
-chemoheterotrophs (mostly saprophytes)
soil impacts:
-slow steady decomposers
-soil aggregate binding with hyphae

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34
Q

what are mycorrhizae?

A

fungi that form a symbiosis with plants (found in 90% of plant species’ roots)
-plant roots provide sugars and a home for fungi
-mycorrhizae provides plants with nutrients, drought tolerance, and pathogen protection

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35
Q

there is also ___________ fungi that eat __________

A

predatory
nematodes (releases enzymes to break down the nematodes)

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36
Q

describe bacteria and archaea

A

-no cell nucleus, asexual reproduction
-very common in soils, esp. bacteria
-smaller than protists and fungi (~0.5-5um)
-the most numerous and diverse organisms as we know it

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37
Q

what are actinomycetes? where are they found?

A

filamentous bacteria (0.5-5um in diameter) that are unicellular heterotrophs
-habitat: most soils, especially arid (alkaline, dry soils)

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38
Q

what functions do actinomycetes do?

A
  1. OM decomposition
  2. produce antibiotics
  3. some are N-fixers
  4. produce geosmin (a molecule that “smells like rain”
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39
Q

what are cyanobacteria (blue green algae)? what habitat are they found in?

A

prokaryotes (most common photoautotrophs)
-no chloroplasts (first photosynthesizers to evolve)
habitat: primarily aquatic, soil surface (0-0.5cm), biological soil crusts

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40
Q

prokaryotes ______ to soil ________

A

adsorb to soil particles (bacteria has a net negative charge and is adsorbed through a cation bridge)

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41
Q

what are soil viruses?

A

contain RNA or DNA with protein exterior
smaller than prokaryotes (most are <0.1um)

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42
Q

list main soil organisms from largest to smallest

A

-earthworms, ants and termites (largest)
-nematodes, mites and springtails
-protists
-fungi
-bacteria and archaea
-viruses (smallest)

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43
Q

what are lichens?

A

a mutualistic symbiosis between algae and fungus and they form the basis of the food chain in some areas.

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44
Q

what are cryptobiotic soil crusts?

A

mutualistic communities of cyanobacteria, mosses and lichens, common in desert soils and they protect soil from erosion, and they provide a significant amount of N to the ecosystem

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45
Q

how do microbes help plants?

A

-SOM formation
-nutrient cycling
-toxin breakdown
-disease suppression

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46
Q

how do microbes harm plants?

A

-herbivorous nematodes
-soil-bourne plant diseases
-deleterious rhizobacteria

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47
Q

what are 3 mutualistic plant-microbe relationships?

A
  1. rhizobia
  2. rhizobacteria
  3. mycorrhizae
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48
Q

what are rhizobia?

A

symbiotic N-fixing bacteria in legume root nodules (convert unavailable N2 from atmosphere to available NH4+)

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49
Q

what are rhizobacteria?

A

all bacteria adapted to living in the rhizosphere (mutualistic, parasitic or commensalism)

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50
Q

what are mycorrhizae?

A

symbiotic fungi found in/on most plant roots (increase P uptake and provide fungi with sugars)

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51
Q

____________ _____________ soils have very healthy microbial populations that help suppress plant pathogens

A

disease suppressive

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52
Q

microbes can let plants know that there are ___________ and allows the plant to release ________ ___________ against the pathogen (induced systematic resistance)

A

pathogens
chemical defenses

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53
Q

what does net carbon pool size equal?

A

change in C = C input - C output

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54
Q

what is the difference between organic C and inorganic C?

A

organic C has C-C and C-H bonds (in SOM: microbial biomass, humus, and detritus)
inorganic C does not have C-C and C-H bonds (soil carbonates: primarily CaCO3 and MgCO3)

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55
Q

what is SOM?

A

material derived from living things in various stages of decomposition (+ microbes)

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56
Q

what does SOM equal?

A

SOM = microbial biomass (living microbial tissue) + detritus (nonliving tissue from plants, animals, fungi, prokaryotes) + humus (decomposed, amorphous, and compost-like)

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57
Q

what soil order has the lowest organic matter?

A

oxisol; in a warm, moist environment like a tropical rainforest, microbes decompose fresh detritus very fast, and the outputs are just as high as the inputs

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58
Q

what is the difference between humus and detritus?

A

detritus: un-decomposed dead roots and other recognizable plant residues (or manure)
humus: mostly large, complex organic molecules with some less complex organics, mostly colloidal with high CEC, amorphous, brown and mushy

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59
Q

what is decomposition?

A

physical breakdown and chemical transformation of large organic molecules into simpler compounds, and synthesis of new compounds from these simple compounds

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60
Q

what are 4 chemical decomposition processes?

A
  1. oxidation: C –> CO2, CH4 + 2O2 –> CO2 + 2H20
  2. release: insoluble (solid, not bioavailable) –> soluble (solution, bioavailable)
  3. synthesis: of new “humic” compounds (tissues, secondary metabolites) by microbes (humification)
  4. protection: protecting new or partially broken-down compounds through physical or chemical means
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61
Q

what type of molecules decomposes slower and faster?

A

simpler and smaller molecules decompose faster:
sugars, starches and simple proteins (fastest)
crude proteins
hemicellulose
cellulose
fats and waxes
lignin’s and phenolic compounds (slowest)

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62
Q

what is mineralization?

A

conversion of a nonmetal from organic to inorganic form (organic nutrient = nutrient bonded to C)
-breaks bond between the nutrient (P, N, S) + C, causing the nutrients to become more plant available

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63
Q

the ______ nitrogen there is in a soil, the faster the decomposition rate

A

more

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64
Q

_________ and ________ have a C/N ratio of 5-10:1

A

microbes and manure
-manure has C/N ratio ~6:1 because it has so many microbes
-bacteria/archaea > actinomycetes/nematodes > fungi

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65
Q

_______ and ___________ have a C/N ratio of 8-15:1

A

SOM and compost
-SOM C/N is lower for subsoils than surface layers
(O horizons have higher C/N ratios of ~40:1)

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66
Q

________ __________ have a C/N ratio of 13-600:1

A

plant residues

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67
Q

-legumes have ________ –> more N –> ________ C/N ratios
-younger and greener plants –> ______ proteins –> _______ C/N ratios
-older, woodier –> _______ lignin –> ________ C/N ratios

A

rhizobia, lower
more, lower
more, higher (slower decomposition)

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68
Q

_________ C/N ratio = faster decomposition
_________ C/N ratio = slower decomposition

A

lower
higher

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69
Q

what happens when C/N ratio is more than 25:1?

A

-N becomes limiting factor to microbial growth
-net N immobilization: inorganic N –> organic N (organic N is N bonded to C)

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70
Q

what happens when the C/N ratio is less than 15:1?

A

-N not limiting at first –> very rapid decomposition
-net N mineralization: organic N –> inorganic N (ammonium or nitrate which is readily available for plant uptake) (mineral N = inorganic N)

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71
Q

what is priming?

A

stimulation of SOM decomposition following addition of fresh C substrates

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72
Q

______________ turns out to be more important than chemical composition on the effect of SOM

A

protection

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73
Q

what is protection?

A

microbes that are prevented from accessing and hence decomposing SOM

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74
Q

what is the difference between chemical and physical protection?

A

chemical protection occurs when SOM is actually stuck between clay particles and is chemically adsorbed to clay versus physical protection is when SOM is physically surrounded by silt or clay particles and the microbe can’t reach it

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75
Q

what are Terra Preta soils?

A

“Amazonian dark earths”, soil rich in SOM and char

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76
Q

what is black carbon?

A

carbon in char, charcoal, soot; degrades very slowly
-pyrolysis (“charring”)
-pyrolysis + oxidation –> combustion (produces oils, gasses, and char)

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77
Q

black carbon, including char is made up of what?

A

pyrolyzed (incompletely combusted) organic materials, usually plants

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78
Q

what soil order is heavy in char?

A

mollisols

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79
Q

what biochar?

A

char for adding to soil (helps acidic soils; its structure enables a very slow decomposition rate)

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80
Q

what are the three soil organic matter carbon pools?

A
  1. active: fast cycling, labile (largest pool)
  2. slow: semi-recalcitrant (medium pool)
  3. passive: very slow cycling, very recalcitrant (smallest pool)
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81
Q

in general, SOM ___________ exponentially with increased depth (except for spodosols)

A

decreases

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82
Q

with increased drainage, there is _______ aeration, _______________ decomposition and _______SOM

A

increased
increased
less

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83
Q

with decreased drainage, there is __________ aeration, __________ decomposition and ______ SOM

A

decreased
decreased
more

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84
Q

drainage of thawed permafrost + wetlands causes what

A

release of CH4 and CO2 (GHG’s)

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85
Q

anaerobic decomposition of SOM is ______ _________ than aerobic decomposition

A

much slower (less O2 –> can’t oxidize CO2 –> less energy)

86
Q

with an increase in soil temperature, there is ______ plant growth, _________ aerobic decomposition (or anaerobic), which causes ________ SOM

A

increased
increased
less

87
Q

with more clay, there is __________ aggregation, _______ protection of SOM, __________ SOM degradation, and ______ SOM

A

increased
better
slower
more

88
Q

what are carbon inputs and outputs for SOM?

A

inputs: plant litter/residues, animal waste, imported bio-products, root residues, rhizodecomposition

outputs: CO2 oxidation, erosion, removal, organic C, leeching and dissolved

89
Q

with more tillage, there is ________ erosion, ____________ SOM outputs, causing _________ SOM

A

more
increased
less

90
Q

with more tillage, there is ____________ aggregation, ________ protection and _________ O2, _________ SOM outputs, resulting in ______ SOM

A

decreased
decreased
more
increased
less

91
Q

with crop harvesting, there is _______ detritus additions, causing a ________ in SOM inputs, and results in _______ SOM

A

decreased
decease
less

92
Q

with crop rows there is ______ bare soil, _________ erosion, __________ SOM outputs which results in ______ SOM

A

more
increased
increased
less

93
Q

after drying to eliminate water in plant litter, which 2 elements account for ~80% of the dry weight?

A

carbon and oxygen

94
Q

under natural vegetation, about 60-90% of SOM is in the __________ fraction

A

passive, very recalcitrant and/or well protected

95
Q

what are the top 4 techniques for managing SOM?

A

-reduced tillage
-organic amendments
-erosion control
-cover crop and perennials

96
Q

conservation tillage leaves _____ of plant residues on the surface

A

~30%

97
Q

with less tillage, there is _______ erosion, __________ aerobic respiration and _____ SOM outputs

A

less
reduced
less

98
Q

increased soil cover and decreased slope –> ________ water flow –> _________ erosion

A

slower
less

99
Q

what are cover crops? what are perennials?

A

cover crops: growing additional crops between growing seasons.
perennials: plants that grow year round

100
Q

with less erosion, there is _______ OM outputs. what are examples of how to control erosion?

A

less
ex: contouring, terracing, and grass strips

101
Q

when plants deposit detritus year-round, there is _______ OM inputs

A

more

102
Q

what are 6 things you can add to soils as an organic input?

A

-sewage sludge
-biowastes
-compost
-biochars
-manure
-grey water

103
Q

what is composting?

A

intentional aerobic breakdown of organic materials outside the soil to form decomposed OM.
-mixed to promote aeration
-reduced weed seeds and pathogens
-optimal C:N ratio (~10)
-has dilute, organic nutrients

104
Q

adequate, not excessive ___________ is best for managing SOM

A

nitrogen

105
Q

how does mulch used to manage SOM?

A

mulch covers the soil and reduces erosion. (only plant-based mulches increase OM inputs)

106
Q

what is soil fertility?

A

ability of a soil to supply nutrients and provide favorable conditions for plant growth

107
Q

what are the macronutrients found in soils?

A

from air and water: C, H + O
from soil: N, P, S, Ca, Mg, K, Si
(greater than 0.1% of plant mass)

108
Q

what are the micronutrients found in soils?

A

from soil: Cu, Fe, Mn, Ni, Zn, Mo, B, Cl, Na, Co
(less than 0.1% of plant mass)

109
Q

both ____________ and ___________ consist of 1-6% of dry plant mass fraction (plants contain ~90% water)

A

nitrogen (N) and potassium (K)

110
Q

explain why nitrogen is so important for plant growth

A
  1. nitrogen is the soil macronutrient that plants use the most and is commonly the most limiting nutrient for plant growth
  2. nitrogen is essential for amino acid, protein, and enzyme synthesis
111
Q

N fertilizers are needed for ____-___% of U.S. food production

A

30-50%

112
Q

nitrogen is readily _______ from agricultural soils: 30% goes into the _________ and 30% goes into ___________

A

lost
atmosphere
groundwater
(nitrogen losses can be reduced but not 100% prevented)

113
Q

how does N pollution from agriculture and industry affect the environment?

A

-water quality
-aquatic biodiversity
-air quality
-human health
-climate change

114
Q

what is a real-world example of how nitrogen affects water quality?

A

the gulf of Mexico’s dead zone (April 2017)

115
Q

what does it mean to be organic nitrogen? what are the most common forms of organic nitrogen?

A

N bound to a C in 1. humus (~5% N) or 2. organisms and detritus (1-20% N) (not plant available)

most common forms:
-urea ((NH4)2CO) (sometimes plant available)
-amines
-amides

116
Q

more than ____% of topsoil N is organic

A

95%

117
Q

what does it mean to be inorganic nitrogen? what are the most common forms of inorganic nitrogen?

A

N not bound to C
in soil solution (ions with charge) (plant available):
-ammonium (NH4+)
-nitrite (NO2-)
-nitrate (NO3-)

in soil air: (not plant available)
-nitrogen gas (N2)
-nitrous oxide (N20) (GHG)
-nitric oxide (NO) (acid rain contributor)
-nitrogen dioxide (NO2)
-ammonia gas (NH3)

118
Q

the smallest pool of nitrogen is more _______ __________ versus the largest pool is _______ ____________

A

plant available
plant unavailable

119
Q

which N pools are a direct source of N for plants?

A
  1. the soil solution
  2. adsorbed to colloid exchange sites
120
Q

describe the size of nitrogen pools from largest to smallest

A

largest: atmosphere –> soil organic nitrogen (SON: microbes, detritus, humus) –> adsorbed to colloids –> dissolved inorganic nitrogen (smallest)

121
Q

generally, what are the 3 main soil N cycling fluxes?

A
  1. additions (inputs): N2 fixation, OM decomposition, rainfall, fertilization
  2. transformations/translocations: immobilization, mineralization, nitrification, desorption, adsorption, downward movement of soluble N in soil profile
  3. losses (outputs): denitrification, NO3- leaching, and NH3 volatilization
122
Q

what is nitrogen fixation?

A

conversion of N2 –> NH3, NH4+, and/or NO3-

123
Q

lots of energy is required to break the triple N bond in N2, where does this energy come from?

A
  1. biotic: microbes
  2. abiotic: lightning or industrial fertilizer synthesis (Haber-Bosch process)
124
Q

___________ living in ________ root nodules convert N2 into NH3 and are responsible for the most biotic N fixation

A

rhizobia
legume
(legumes = pea family (Fabaceae plants –> beans, chickpeas, lentils, peanuts, clover, and mesquite))

125
Q

some ___________ also fix N for shrubs and trees (ex: Frankia in alder trees)

A

actinomycetes (filamentous bacteria)

126
Q

______ _________ N fixing bacteria also fix some N

A

free living
(non-symbiotic is much less abundant)
(cyanobacteria and some heterotrophs)

127
Q

symbiotic land plant fixation is ______ _________ than non-symbiotic fixation

A

more abundant
(rhizobium + legumes –> cyanobacteria –> free living)

128
Q

what 5 processes are considered to be an addition in the nitrogen cycle?

A
  1. haber-bosch process (N2 fixation)
  2. lightning (N2 fixation)
  3. rhizobia and frankia (N2 fixation)
  4. acid rain (N deposition)
  5. fertilization//OM application
129
Q

how does lightning fix nitrogen?

A

lots of naturally supplied heat and energy breaks the N-N triple bond in N2 and allows N to react with O in atmosphere to form NO and NO2. (abiotic and natural N fixation)

130
Q

how does the haber-bosch process fix nitrogen?

A

N2 gas is reacted with H2 gas under high heat conditions to break the N-N triple bond and form NH3 (abiotic and anthropogenic N fixation)
(50% of all global N2 fixation)

131
Q

how does acid rain contribute to N deposition?

A

combustion of fossil fuels leads to SOx and NOx emissions. the SOx and NOx then react with H20 in the atmosphere to produce sulfuric and nitric acids. these acids then dissociate and produce loose H+ ions which lowers the pH of water droplets in the air which then coalesce and fall to the ground and into soils

132
Q

what are organic nitrogen additions?

A
  1. organic fertilizers (synthetic urea)
  2. composts, mulches, plant residues
  3. manure (human applied, deposited by animals)
  4. wastes (grey water, urine, biosolids (from sewage treatment plants))
133
Q

what 5 general processes are considered transformations and translocations?

A
  1. N uptake by plants
  2. mineralization
  3. immobilization
  4. nitrification (ammonium oxidation)
  5. adsorption and desorption
134
Q

plants take up mostly ________ and _________ and some urea. plants use ___________ N to synthesize ___________ N (proteins, enzymes, etc)

A

NO3- and NH4+ (both plant available)
inorganic
organic

135
Q

mineralization and immobilization occur ____________

A

simultaneously

136
Q

N ___________ makes N available to plants and is favored by OM with a C:N ratio of _________

A

mineralization (organic N –> inorganic N)
less than 15:1

137
Q

N ____________ makes N unavailable to plants and is favored by OM with a C:N ratio of _____________

A

immobilization (inorganic N –> organic N)
greater than 25:1

138
Q

when is there more inorganic N? when is there less inorganic N?

A

mineralization > immobilization = more inorganic N
immobilization > mineralization = less inorganic N

139
Q

what is nitrification?

A

oxidation of ammonium to nitrite and then nitrate
(NH4+ –> NO3-)

140
Q

when is the process of nitrification the fastest?

A

oxidizing conditions (abundant O2 and well aerated soils)

141
Q

(adsorption and desorption) ammonium exhibits _________ exchange and nitrate and nitrite exhibit _________ exchange

A

cation exchange
anion exchange

142
Q

in most soils, NH4+ adsorbs __________ than NO3-

A

stronger (CEC>AEC)

143
Q

which processes increase concentration of plant-available N in soil?

A
  1. mineralization
  2. acid rain
  3. nitrogen fixation
  4. adding ammonium nitrate fertilizer
144
Q

what 3 processes are involved in N losses?

A
  1. NO3- (nitrate) leaching
  2. denitrification
  3. NH3 volatilization
145
Q

what is leaching?

A

removal of dissolved solutes from soil by percolating water (most leached N is lost from NO3-)

146
Q

when are N leaching losses the fastest?

A

sandy soil where most N is NO3-

147
Q

what is denitrification?

A

reduction of NO3- to N2 gas (NO3- –> NO2- –> N2O –> N2)

148
Q

when is denitrification the most common?

A

saturated soils (anaerobic conditions)

149
Q

what is volatilization?

A

volatilization is the loss of N through the conversion of ammonium to ammonia gas (NH3) which is a volatile gas.

150
Q

with an increase in pH and temperature, there is a ____________ in NH3 volatilization

A

an increase

151
Q

in most natural ecosystems, there is ______ N inputs and ______ N losses. most N is tied up where?

A

low
low
most N is tied up in plant biomass and soil organic matter

152
Q

in conventional agricultural systems, there is ______ N inputs and ______ N losses. typically, not more than ___-____% of N fertilizers applied are taken up by plants because of ….

A

high
high
30-70%
leeching, denitrification, and NH3 volatilization losses

153
Q

nitrogen fertilizers account for _____ of global fixed N (Haber-bosh process) which has resulted in an increase in ___ ___________

A

1/2
N pollution (GHG: N2O) which increases acid rain (NO and NO2) and negatively affects our water supply

154
Q

what is the largest source of N?
how much N is needed that is not met?

A

legumes: 15.6 billion of lbs/year
13.3 billion of lbs/year is not met

155
Q

almost twice as much N fertilizer is used than is required by crops, why?

A

because there is so much N losses (decreased efficiency)

156
Q

what are inorganic N fertilizers vs. organic N fertilizers?

A

inorganic: made via Haber-bosch process
gas: pressurized NH3 that can be injected into the soil
liquids: NH3 or salts dissolved in irrigation water
solids: salts of N (NH4)2SO4, NH4NO3, KNO3

organic:
-sewage sludge, animal manure, organic wastes
-urea (synthetic)

157
Q

nitrogen losses are ____________
NH4+ fertilizers = _______ lost
NO3- fertilizers = ______ lost

A

inevitable
less (due to increased adsorption)
more (due to increased leaching)

158
Q

proper management is essential for efficient use of N fertilizers, how can we practice proper management?

A
  1. incorporate NH4+ fertilizers
  2. do not over irrigate (increased leaching)
  3. synchronize fertilizer application with plant needs
159
Q

what is the importance of sulfur in terms of soil organisms?

A

-found in some amino acids and enzymes
-plant tissues have 0.1-1.5% S

160
Q

what do plant sulfur deficiencies cause?

A
  1. chlorosis (yellowing) especially of new leaves
  2. thin stems
161
Q

~____% of H+ ions in acid rain is due to ______ gases

A

~60%
SOx

162
Q

what is the importance of sulfur in acid mine tailings and drained wetlands?

A

mine tailings and wetland soils often contain reduced forms of S which react with O2 and gets oxidized and results in acidification (due to increased H+ ions)

163
Q

what are forms of sulfur in the atmosphere?

A

-sulfur dioxide (SO2) from combustion and volcanoes
-hydrogen sulfide (H2S) (stinky gas) from volcanoes and hot springs and wetlands
-other trace amounts: carbonyl sulfide (COS) and various others (SOx)

164
Q

what are inorganic forms of S in soil (both reduced and oxidized forms)? where are they found?

A

reduced forms
-elemental S = So
-sulfide = S2
-disulfide = S2 2-
found in very low O2 (anoxic) environments
-readily oxidized –> severe acidification
-mostly insoluble

oxidized forms:
-sulfate (SO4 2-), most common S form found in:
-aerobic soils, desert soils, most natural water bodies
-does not cause acidification
-very soluble

165
Q

what are the mineral forms of inorganic S?

A

-iron sulfide (FeS)
-pyrite (FeS2)
-jarosite (KFe3 3+ (OH)6 (SO4)2)
-gypsum (CaSO4 2H2O) (very soluble)
-anhydrite (CaSO4) (very soluble)

166
Q

most soils have more _________ S than ___________ S

A

organic
inorganic
(organic S is 90-98% of soil S in temperate soils (exception: aridisols, ultisols and oxisols))

167
Q

where is organic S found in soils?

A
  1. amino acids: methionine, cysteine, and cystine (in living biomass and detritus)
  2. coenzyme A (used in fatty acid synthesis and Krebs cycle)
  3. soil humus
168
Q

both sulfate and sulfide are _____________ and ___________

A

dissolved and bioavailable

169
Q

what are main 4 sulfur additions to the soil?

A

-manure
-detritus
-fertilizer
-acid rain

170
Q

explain how acid rain works in terms of sulfur

A
  1. SOx (SO2 and SO3) is produced during fossil fuel combustion
  2. SOx reacts with O2 and H20 in the atmosphere to form sulfuric acid
  3. sulfuric acid then dissociates and forms H+ and SO4 2- ions which causes acidification due to H+
171
Q

when is sulfur oxidized versus reduced?

A

oxidation: S0, S2- –> SO4 2-
reduction: SO4 2- –> S0, S2

172
Q

if S is bonded to O, it is _____________
if S is not bonded to O, it is typically _____________

A

oxidized
reduced

173
Q

oxidation of S occurs under what conditions? what does it produce/consume and result in?

A

conditions: any O2 and increased aeration
-produces H+ –> acidification (pH decreases)

174
Q

reduction of S occurs under what conditions? what does it produce/consume and result in?

A

conditions: no O2 and very low aeration
-consumes H+ –> alkalization (pH increases)

175
Q

what are the types of sulfur transformations?

A
  1. mineralization: organic S –> inorganic S
  2. immobilization: inorganic S –> organic S
  3. adsorption: sticking to soil colloid
  4. desorption: unsticking to soil colloid
  5. precipitation: rain, snow, hail
  6. dissolution
176
Q

________ is available to plants

A

sulfate (SO4 2-) (inorganic S)

177
Q

with a decrease in pH, there is _______ sulfate ____________

A

more sulfate sorption

178
Q

what are types of sulfur losses?

A
  1. combustion: only combustion of plants (like firewood) not fossil fuels
  2. erosion and runoff: sulfur flowing off the soil with water
  3. sulfate leaching: sulfur flowing down through the soil to the water table beneath
179
Q

where is sulfur deficiency the most common?

A

-sandy soils
-low organic matter soils
-highly leached soils

180
Q

where is sulfur generally sufficient in?

A

-desert soils
-irrigated soils (bc irrigation water contains sulfate and other salts)

181
Q

what is the general significance of phosphorus?

A

-P is the 2nd most limiting nutrient to plant growth in terrestrial ecosystems (after N)
-usually the most limiting nutrient in freshwater ecosystems
-in ATP, RNA, and DNA
-needed to build bones

182
Q

phosphorus only has one __________ form in soil, what is it?

A

inorganic
-phosphate ion (PO4 3-) (ions, salts and minerals)

183
Q

phosphorus does not have any ________ forms

A

gaseous

184
Q

total soil P contents is usually _______

A

low (plants use about 1/10th as much P as N)
-soils usually contain 200-2000 kg/ha of P

185
Q

most soil P (at least 50%) is in ________ forms, where are the exceptions?

A

inorganic
exception: histosols and O horizons
mostly insoluble –> unavailable to plants

186
Q

the largest pools of P are __________ minerals and ______________. only the _______ ____________ is available for plants

A

insoluble minerals and organic P
soil solution (smallest pool)

187
Q

phosphate is ______________

A

nonexchangeable (and therefore not plant available)

188
Q

what is the biggest loss for phosphorus?

A

loss due to erosion

189
Q

is there a phosphorus pool in the atmosphere?

A

no

190
Q

plants use the phosphate ions H2PO4- and HPO4 2-. the ____________ between the two forms is controlled by ______

A

distribution
pH

191
Q

describe the problem with phosphorus

A

phosphorus is only soluble between pH 6-7. (only ~0.01% of total soil P is bioavailable because of low solubility)
-with a high pH, P will precipitate with Ca and Mg
-with a low pH, P will precipitate with Al, Fe, and Mn

192
Q

P __________ occurs when P precipitates with Fe, Al, Mn, Ca or Mg

A

fixation

193
Q

where is phosphorus deficiency a major problem?

A

in acidic tropical soils and some alkaline soils (when soil pH is either too low or too high)

194
Q

what is the largest relative loss sizes? smallest?

A

largest: loss due to eroded particles
middle: loss due to runoff
smallest: loss due to leaching

195
Q

due to the low solubility of P, it does not ________ across long distances easily and becomes depleted near roots and hyphae

A

diffuse

196
Q

usually less than ______% of applied P is taken up by plants because of ______ solubility

A

30%
low

197
Q

what are 3 things that we can do to increase P plant-availability?

A

-maintain pH at 6-7 (increases solubility)
-apply P near plant roots (decreases diffusion)
-add OM (blocks P sorption and precipitation)

198
Q

what factors affect P availability?

A

-soil pH (maximized at pH 6-6.5, good from 6-7)
-Ca, Fe, and Al minerals (more Ca –> less available at high pH + more Fe and Al –> less P available at low pH)
-soil temperature (colder –> P less soluble –> less available)
-soil moisture (wetter –> more P dissolves –> more available)

199
Q

what is the most common phosphorus mineral and fertilizer?

A

mineral: hydroxyapatite (in phosphorite rock “rock phosphate”) mined and found in bones
fertilizers: Ca(H2PO4)2, NH4H2PO4 or (NH4)2HPO4

200
Q

there is also phosphorus in _________

A

manure; animal manures have high P concentrations relative to other nutrients (in order to meet plant N needs with manure –> too much P)
(CAFO: confined animal feeding operation = major source of P pollution)

201
Q

how does P pollution occur and why is P pollution harmful?

A

it’s typically too expensive to transport the manure far distances so manure is typically given away for free and then farmers near the livestock areas end up applying way too much P.
too much P application = P buildup in soils and eventually pollutes nearby water bodies (eutrophication)

202
Q

what are the effects of P eutrophication?

A

too much P runoff in freshwater systems causes (photoautotrophs) rapid algal blooms, followed by algal death which causes decomposition and hypoxia. Then the fish in the water don’t get enough oxygen (due to hypoxic conditions) and this causes a die-off of a lot of aquatic organisms
(specifically due to P in freshwater)

203
Q

what are the 4 main sources of P in water?

A

-erosion
-waste
-fertilizer
-soaps and detergents

204
Q

what are things we can do to control/limit P pollution?

A

-limit P application (to meet plant needs)
-reduce rates of soil erosion
-prevent waste leaks
-use P-free detergents

205
Q

of the dry fraction, plants on average have ___-___% potassium (K)?

A

1-6%

206
Q

what is the importance of K?

A

-enzyme activator for all organisms
in plants:
-osmotic potential regulator (important for water transport)
-maintains charge balance (important for sugar transport)
-stress residence (drought and disease)

207
Q

K loss from soil does not cause serious ____________ ____________

A

environmental issues

208
Q

what are the soil K pools and how big are they?

A

not plant available:
-minerals (largest sized pool, mostly feldspar and mica (structural K))
-“fixed” (trapped in clay interlayers)
plant available:
-exchangeable (salt-replaceable, expanding clay-interlayers, external surfaces
-soil solution (smallest pool, K+ salts (readily soluble))

209
Q

does K have a gas form?

A

no gas form (no atmospheric pool)
only solid and aqueous forms

210
Q

what are potassium losses?

A

-erosion (only in exchangeable forms)
-runoff (soil solution)
-leaching (soil solution)

211
Q

where are K-depleted soils found?

A

places with increased precipitation (which causes increased erosion, runoff and leaching losses)
-lower pH/acidic soils = increased leaching due to more + charges

212
Q
A

ENVS 200 (3 decks)

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