Exam #3 Flashcards
what are the three domains of life?
-eukaryota
-bacteria
-archaea
generally, what type of organisms are eukaryotes?
fungi, protists, plants, and animals (membrane bound organelles with nucleus)
what type of organisms are prokaryotes?
archaea and bacteria (don’t have membrane-bound organelles)
describe the kingdom protista
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.
describe the soil trophic levels
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)
what are the different size classes of soil organisms?
- macro-organisms (>2 mm)
- meso-organisms (0.1-2mm)
- micro-organisms (<0.1mm)
what organisms are considered macro-organisms?
-plant roots
-burrowing animals
-earthworms
-ants and termites
__________ _______ are macro-organisms which are ____-____ of plant mass. they are ___-______ um in diameter
plant roots
30-50%
10-400
how do plant roots enrich SOM?
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
what is the rhizosphere? what does the rhizosphere has more of compared to non-rhizosphere soil?
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)
describe burrowing animals that contribute to macro-organisms and how they impact soils
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
ants and termites have multiple ecological roles (herbivores, predators and detritivores), how do their nests impact soils?
-improved soil aeration
-increased infiltration
-modify soil pH
-local enrichment of nutrients
(habitat for ants: temperate, for termites: hot, dry)
what habitat are earthworms (Annelida) found in? what are their functions?
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)
what are different types of meso-organisms?
rotifers
springtails and mites
tardigrades (“water bears”)
nematodes (unsegmented worms found in almost all soils)
protozoa
describe protozoa and where you might find them
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
what 4 things do all organisms need to survive?
-electron acceptor (oxidizing agent)
-carbon source
-water
-mineral nutrients
where do autotrophs get their carbon/energy from?
C from inorganic compounds (CO2 or CO3 2-)
where do heterotrophs get their carbon/energy from?
C from organic compounds (with C-C and C-H bonds)
where do chemotrophs get their energy from?
energy (e-) from chemicals
where do phototrophs get their energy from?
energy (e-) from light
what are chemoheterotrophs?
energy source from biochemical oxidation and carbon source from organic materials (all fungi, all animals, most bacteria)
what are chemoautotrophs?
energy source from biochemical oxidation and carbon source from CO2 (deep ocean microbes, N + S oxidizers)
what are photoheterotrophs?
energy source from sunlight and carbon source from organic materials (some bacteria, algae and protists)
what are photoautotrophs?
energy source from sunlight and carbon source from inorganic CO2 (algae, cyanobacteria, and higher plants)
what 8 environmental conditions affect soil microbial growth and activity?
- organic substrates
- nutrient substrates
- oxygen/redox status
- temperature and sunlight
- moisture
- pH
- salinity
- toxins
what is the Baas-Becking Hypothesis?
everything is everywhere but the environment selects
most soil microbes prefer when soil water content is near ________ __________
field capacity (too dry = microbes can’t get water or solutes)
how does soil aeration affect soil microbes?
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+)
what is the ideal pH and temperature range for soil microbes?
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)
simple substrates are decomposed _____ _______ than complex substrates, like cellulose and lignin.
_________ decompose cellulose and lignin more effectively than __________
more rapidly
fungi
bacteria
what are algae, what effect do algae have on soils, and what habitat are they found in?
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)
what are slime molds? where are they found in the soil?
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
what are fungi? what impact does fungi have on soils?
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
what are mycorrhizae?
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
there is also ___________ fungi that eat __________
predatory
nematodes (releases enzymes to break down the nematodes)
describe bacteria and archaea
-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
what are actinomycetes? where are they found?
filamentous bacteria (0.5-5um in diameter) that are unicellular heterotrophs
-habitat: most soils, especially arid (alkaline, dry soils)
what functions do actinomycetes do?
- OM decomposition
- produce antibiotics
- some are N-fixers
- produce geosmin (a molecule that “smells like rain”
what are cyanobacteria (blue green algae)? what habitat are they found in?
prokaryotes (most common photoautotrophs)
-no chloroplasts (first photosynthesizers to evolve)
habitat: primarily aquatic, soil surface (0-0.5cm), biological soil crusts
prokaryotes ______ to soil ________
adsorb to soil particles (bacteria has a net negative charge and is adsorbed through a cation bridge)
what are soil viruses?
contain RNA or DNA with protein exterior
smaller than prokaryotes (most are <0.1um)
list main soil organisms from largest to smallest
-earthworms, ants and termites (largest)
-nematodes, mites and springtails
-protists
-fungi
-bacteria and archaea
-viruses (smallest)
what are lichens?
a mutualistic symbiosis between algae and fungus and they form the basis of the food chain in some areas.
what are cryptobiotic soil crusts?
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
how do microbes help plants?
-SOM formation
-nutrient cycling
-toxin breakdown
-disease suppression
how do microbes harm plants?
-herbivorous nematodes
-soil-bourne plant diseases
-deleterious rhizobacteria
what are 3 mutualistic plant-microbe relationships?
- rhizobia
- rhizobacteria
- mycorrhizae
what are rhizobia?
symbiotic N-fixing bacteria in legume root nodules (convert unavailable N2 from atmosphere to available NH4+)
what are rhizobacteria?
all bacteria adapted to living in the rhizosphere (mutualistic, parasitic or commensalism)
what are mycorrhizae?
symbiotic fungi found in/on most plant roots (increase P uptake and provide fungi with sugars)
____________ _____________ soils have very healthy microbial populations that help suppress plant pathogens
disease suppressive
microbes can let plants know that there are ___________ and allows the plant to release ________ ___________ against the pathogen (induced systematic resistance)
pathogens
chemical defenses
what does net carbon pool size equal?
change in C = C input - C output
what is the difference between organic C and inorganic C?
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)
what is SOM?
material derived from living things in various stages of decomposition (+ microbes)
what does SOM equal?
SOM = microbial biomass (living microbial tissue) + detritus (nonliving tissue from plants, animals, fungi, prokaryotes) + humus (decomposed, amorphous, and compost-like)
what soil order has the lowest organic matter?
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
what is the difference between humus and detritus?
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
what is decomposition?
physical breakdown and chemical transformation of large organic molecules into simpler compounds, and synthesis of new compounds from these simple compounds
what are 4 chemical decomposition processes?
- oxidation: C –> CO2, CH4 + 2O2 –> CO2 + 2H20
- release: insoluble (solid, not bioavailable) –> soluble (solution, bioavailable)
- synthesis: of new “humic” compounds (tissues, secondary metabolites) by microbes (humification)
- protection: protecting new or partially broken-down compounds through physical or chemical means
what type of molecules decomposes slower and faster?
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)
what is mineralization?
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
the ______ nitrogen there is in a soil, the faster the decomposition rate
more
_________ and ________ have a C/N ratio of 5-10:1
microbes and manure
-manure has C/N ratio ~6:1 because it has so many microbes
-bacteria/archaea > actinomycetes/nematodes > fungi
_______ and ___________ have a C/N ratio of 8-15:1
SOM and compost
-SOM C/N is lower for subsoils than surface layers
(O horizons have higher C/N ratios of ~40:1)
________ __________ have a C/N ratio of 13-600:1
plant residues
-legumes have ________ –> more N –> ________ C/N ratios
-younger and greener plants –> ______ proteins –> _______ C/N ratios
-older, woodier –> _______ lignin –> ________ C/N ratios
rhizobia, lower
more, lower
more, higher (slower decomposition)
_________ C/N ratio = faster decomposition
_________ C/N ratio = slower decomposition
lower
higher
what happens when C/N ratio is more than 25:1?
-N becomes limiting factor to microbial growth
-net N immobilization: inorganic N –> organic N (organic N is N bonded to C)
what happens when the C/N ratio is less than 15:1?
-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)
what is priming?
stimulation of SOM decomposition following addition of fresh C substrates
______________ turns out to be more important than chemical composition on the effect of SOM
protection
what is protection?
microbes that are prevented from accessing and hence decomposing SOM
what is the difference between chemical and physical protection?
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
what are Terra Preta soils?
“Amazonian dark earths”, soil rich in SOM and char
what is black carbon?
carbon in char, charcoal, soot; degrades very slowly
-pyrolysis (“charring”)
-pyrolysis + oxidation –> combustion (produces oils, gasses, and char)
black carbon, including char is made up of what?
pyrolyzed (incompletely combusted) organic materials, usually plants
what soil order is heavy in char?
mollisols
what biochar?
char for adding to soil (helps acidic soils; its structure enables a very slow decomposition rate)
what are the three soil organic matter carbon pools?
- active: fast cycling, labile (largest pool)
- slow: semi-recalcitrant (medium pool)
- passive: very slow cycling, very recalcitrant (smallest pool)
in general, SOM ___________ exponentially with increased depth (except for spodosols)
decreases
with increased drainage, there is _______ aeration, _______________ decomposition and _______SOM
increased
increased
less
with decreased drainage, there is __________ aeration, __________ decomposition and ______ SOM
decreased
decreased
more
drainage of thawed permafrost + wetlands causes what
release of CH4 and CO2 (GHG’s)
anaerobic decomposition of SOM is ______ _________ than aerobic decomposition
much slower (less O2 –> can’t oxidize CO2 –> less energy)
with an increase in soil temperature, there is ______ plant growth, _________ aerobic decomposition (or anaerobic), which causes ________ SOM
increased
increased
less
with more clay, there is __________ aggregation, _______ protection of SOM, __________ SOM degradation, and ______ SOM
increased
better
slower
more
what are carbon inputs and outputs for SOM?
inputs: plant litter/residues, animal waste, imported bio-products, root residues, rhizodecomposition
outputs: CO2 oxidation, erosion, removal, organic C, leeching and dissolved
with more tillage, there is ________ erosion, ____________ SOM outputs, causing _________ SOM
more
increased
less
with more tillage, there is ____________ aggregation, ________ protection and _________ O2, _________ SOM outputs, resulting in ______ SOM
decreased
decreased
more
increased
less
with crop harvesting, there is _______ detritus additions, causing a ________ in SOM inputs, and results in _______ SOM
decreased
decease
less
with crop rows there is ______ bare soil, _________ erosion, __________ SOM outputs which results in ______ SOM
more
increased
increased
less
after drying to eliminate water in plant litter, which 2 elements account for ~80% of the dry weight?
carbon and oxygen
under natural vegetation, about 60-90% of SOM is in the __________ fraction
passive, very recalcitrant and/or well protected
what are the top 4 techniques for managing SOM?
-reduced tillage
-organic amendments
-erosion control
-cover crop and perennials
conservation tillage leaves _____ of plant residues on the surface
~30%
with less tillage, there is _______ erosion, __________ aerobic respiration and _____ SOM outputs
less
reduced
less
increased soil cover and decreased slope –> ________ water flow –> _________ erosion
slower
less
what are cover crops? what are perennials?
cover crops: growing additional crops between growing seasons.
perennials: plants that grow year round
with less erosion, there is _______ OM outputs. what are examples of how to control erosion?
less
ex: contouring, terracing, and grass strips
when plants deposit detritus year-round, there is _______ OM inputs
more
what are 6 things you can add to soils as an organic input?
-sewage sludge
-biowastes
-compost
-biochars
-manure
-grey water
what is composting?
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
adequate, not excessive ___________ is best for managing SOM
nitrogen
how does mulch used to manage SOM?
mulch covers the soil and reduces erosion. (only plant-based mulches increase OM inputs)
what is soil fertility?
ability of a soil to supply nutrients and provide favorable conditions for plant growth
what are the macronutrients found in soils?
from air and water: C, H + O
from soil: N, P, S, Ca, Mg, K, Si
(greater than 0.1% of plant mass)
what are the micronutrients found in soils?
from soil: Cu, Fe, Mn, Ni, Zn, Mo, B, Cl, Na, Co
(less than 0.1% of plant mass)
both ____________ and ___________ consist of 1-6% of dry plant mass fraction (plants contain ~90% water)
nitrogen (N) and potassium (K)
explain why nitrogen is so important for plant growth
- nitrogen is the soil macronutrient that plants use the most and is commonly the most limiting nutrient for plant growth
- nitrogen is essential for amino acid, protein, and enzyme synthesis
N fertilizers are needed for ____-___% of U.S. food production
30-50%
nitrogen is readily _______ from agricultural soils: 30% goes into the _________ and 30% goes into ___________
lost
atmosphere
groundwater
(nitrogen losses can be reduced but not 100% prevented)
how does N pollution from agriculture and industry affect the environment?
-water quality
-aquatic biodiversity
-air quality
-human health
-climate change
what is a real-world example of how nitrogen affects water quality?
the gulf of Mexico’s dead zone (April 2017)
what does it mean to be organic nitrogen? what are the most common forms of organic nitrogen?
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
more than ____% of topsoil N is organic
95%
what does it mean to be inorganic nitrogen? what are the most common forms of inorganic nitrogen?
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)
the smallest pool of nitrogen is more _______ __________ versus the largest pool is _______ ____________
plant available
plant unavailable
which N pools are a direct source of N for plants?
- the soil solution
- adsorbed to colloid exchange sites
describe the size of nitrogen pools from largest to smallest
largest: atmosphere –> soil organic nitrogen (SON: microbes, detritus, humus) –> adsorbed to colloids –> dissolved inorganic nitrogen (smallest)
generally, what are the 3 main soil N cycling fluxes?
- additions (inputs): N2 fixation, OM decomposition, rainfall, fertilization
- transformations/translocations: immobilization, mineralization, nitrification, desorption, adsorption, downward movement of soluble N in soil profile
- losses (outputs): denitrification, NO3- leaching, and NH3 volatilization
what is nitrogen fixation?
conversion of N2 –> NH3, NH4+, and/or NO3-
lots of energy is required to break the triple N bond in N2, where does this energy come from?
- biotic: microbes
- abiotic: lightning or industrial fertilizer synthesis (Haber-Bosch process)
___________ living in ________ root nodules convert N2 into NH3 and are responsible for the most biotic N fixation
rhizobia
legume
(legumes = pea family (Fabaceae plants –> beans, chickpeas, lentils, peanuts, clover, and mesquite))
some ___________ also fix N for shrubs and trees (ex: Frankia in alder trees)
actinomycetes (filamentous bacteria)
______ _________ N fixing bacteria also fix some N
free living
(non-symbiotic is much less abundant)
(cyanobacteria and some heterotrophs)
symbiotic land plant fixation is ______ _________ than non-symbiotic fixation
more abundant
(rhizobium + legumes –> cyanobacteria –> free living)
what 5 processes are considered to be an addition in the nitrogen cycle?
- haber-bosch process (N2 fixation)
- lightning (N2 fixation)
- rhizobia and frankia (N2 fixation)
- acid rain (N deposition)
- fertilization//OM application
how does lightning fix nitrogen?
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)
how does the haber-bosch process fix nitrogen?
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)
how does acid rain contribute to N deposition?
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
what are organic nitrogen additions?
- organic fertilizers (synthetic urea)
- composts, mulches, plant residues
- manure (human applied, deposited by animals)
- wastes (grey water, urine, biosolids (from sewage treatment plants))
what 5 general processes are considered transformations and translocations?
- N uptake by plants
- mineralization
- immobilization
- nitrification (ammonium oxidation)
- adsorption and desorption
plants take up mostly ________ and _________ and some urea. plants use ___________ N to synthesize ___________ N (proteins, enzymes, etc)
NO3- and NH4+ (both plant available)
inorganic
organic
mineralization and immobilization occur ____________
simultaneously
N ___________ makes N available to plants and is favored by OM with a C:N ratio of _________
mineralization (organic N –> inorganic N)
less than 15:1
N ____________ makes N unavailable to plants and is favored by OM with a C:N ratio of _____________
immobilization (inorganic N –> organic N)
greater than 25:1
when is there more inorganic N? when is there less inorganic N?
mineralization > immobilization = more inorganic N
immobilization > mineralization = less inorganic N
what is nitrification?
oxidation of ammonium to nitrite and then nitrate
(NH4+ –> NO3-)
when is the process of nitrification the fastest?
oxidizing conditions (abundant O2 and well aerated soils)
(adsorption and desorption) ammonium exhibits _________ exchange and nitrate and nitrite exhibit _________ exchange
cation exchange
anion exchange
in most soils, NH4+ adsorbs __________ than NO3-
stronger (CEC>AEC)
which processes increase concentration of plant-available N in soil?
- mineralization
- acid rain
- nitrogen fixation
- adding ammonium nitrate fertilizer
what 3 processes are involved in N losses?
- NO3- (nitrate) leaching
- denitrification
- NH3 volatilization
what is leaching?
removal of dissolved solutes from soil by percolating water (most leached N is lost from NO3-)
when are N leaching losses the fastest?
sandy soil where most N is NO3-
what is denitrification?
reduction of NO3- to N2 gas (NO3- –> NO2- –> N2O –> N2)
when is denitrification the most common?
saturated soils (anaerobic conditions)
what is volatilization?
volatilization is the loss of N through the conversion of ammonium to ammonia gas (NH3) which is a volatile gas.
with an increase in pH and temperature, there is a ____________ in NH3 volatilization
an increase
in most natural ecosystems, there is ______ N inputs and ______ N losses. most N is tied up where?
low
low
most N is tied up in plant biomass and soil organic matter
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 ….
high
high
30-70%
leeching, denitrification, and NH3 volatilization losses
nitrogen fertilizers account for _____ of global fixed N (Haber-bosh process) which has resulted in an increase in ___ ___________
1/2
N pollution (GHG: N2O) which increases acid rain (NO and NO2) and negatively affects our water supply
what is the largest source of N?
how much N is needed that is not met?
legumes: 15.6 billion of lbs/year
13.3 billion of lbs/year is not met
almost twice as much N fertilizer is used than is required by crops, why?
because there is so much N losses (decreased efficiency)
what are inorganic N fertilizers vs. organic N fertilizers?
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)
nitrogen losses are ____________
NH4+ fertilizers = _______ lost
NO3- fertilizers = ______ lost
inevitable
less (due to increased adsorption)
more (due to increased leaching)
proper management is essential for efficient use of N fertilizers, how can we practice proper management?
- incorporate NH4+ fertilizers
- do not over irrigate (increased leaching)
- synchronize fertilizer application with plant needs
what is the importance of sulfur in terms of soil organisms?
-found in some amino acids and enzymes
-plant tissues have 0.1-1.5% S
what do plant sulfur deficiencies cause?
- chlorosis (yellowing) especially of new leaves
- thin stems
~____% of H+ ions in acid rain is due to ______ gases
~60%
SOx
what is the importance of sulfur in acid mine tailings and drained wetlands?
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)
what are forms of sulfur in the atmosphere?
-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)
what are inorganic forms of S in soil (both reduced and oxidized forms)? where are they found?
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
what are the mineral forms of inorganic S?
-iron sulfide (FeS)
-pyrite (FeS2)
-jarosite (KFe3 3+ (OH)6 (SO4)2)
-gypsum (CaSO4 2H2O) (very soluble)
-anhydrite (CaSO4) (very soluble)
most soils have more _________ S than ___________ S
organic
inorganic
(organic S is 90-98% of soil S in temperate soils (exception: aridisols, ultisols and oxisols))
where is organic S found in soils?
- amino acids: methionine, cysteine, and cystine (in living biomass and detritus)
- coenzyme A (used in fatty acid synthesis and Krebs cycle)
- soil humus
both sulfate and sulfide are _____________ and ___________
dissolved and bioavailable
what are main 4 sulfur additions to the soil?
-manure
-detritus
-fertilizer
-acid rain
explain how acid rain works in terms of sulfur
- SOx (SO2 and SO3) is produced during fossil fuel combustion
- SOx reacts with O2 and H20 in the atmosphere to form sulfuric acid
- sulfuric acid then dissociates and forms H+ and SO4 2- ions which causes acidification due to H+
when is sulfur oxidized versus reduced?
oxidation: S0, S2- –> SO4 2-
reduction: SO4 2- –> S0, S2
if S is bonded to O, it is _____________
if S is not bonded to O, it is typically _____________
oxidized
reduced
oxidation of S occurs under what conditions? what does it produce/consume and result in?
conditions: any O2 and increased aeration
-produces H+ –> acidification (pH decreases)
reduction of S occurs under what conditions? what does it produce/consume and result in?
conditions: no O2 and very low aeration
-consumes H+ –> alkalization (pH increases)
what are the types of sulfur transformations?
- mineralization: organic S –> inorganic S
- immobilization: inorganic S –> organic S
- adsorption: sticking to soil colloid
- desorption: unsticking to soil colloid
- precipitation: rain, snow, hail
- dissolution
________ is available to plants
sulfate (SO4 2-) (inorganic S)
with a decrease in pH, there is _______ sulfate ____________
more sulfate sorption
what are types of sulfur losses?
- combustion: only combustion of plants (like firewood) not fossil fuels
- erosion and runoff: sulfur flowing off the soil with water
- sulfate leaching: sulfur flowing down through the soil to the water table beneath
what is the largest loss for S?
leaching
where is sulfur deficiency the most common?
-sandy soils
-low organic matter soils
-highly leached soils
where is sulfur generally sufficient in?
-desert soils
-irrigated soils (bc irrigation water contains sulfate and other salts)
what is the general significance of phosphorus?
-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
phosphorus only has one __________ form in soil, what is it?
inorganic
-phosphate ion (PO4 3-) (ions, salts and minerals)
phosphorus does not have any ________ forms
gaseous
total soil P contents is usually _______
low (plants use about 1/10th as much P as N)
-soils usually contain 200-2000 kg/ha of P
most soil P (at least 50%) is in ________ forms, where are the exceptions?
inorganic
exception: histosols and O horizons
mostly insoluble –> unavailable to plants
the largest pools of P are __________ minerals and ______________. only the _______ ____________ is available for plants
insoluble minerals and organic P
soil solution (smallest pool)
phosphate is ______________
nonexchangeable (and therefore not plant available)
what is the biggest loss for phosphorus?
loss due to erosion and runoff
is there a phosphorus pool in the atmosphere?
no
plants use the phosphate ions H2PO4- and HPO4 2-. the ____________ between the two forms is controlled by ______
distribution
pH
describe the problem with phosphorus
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
P __________ occurs when P precipitates with Fe, Al, Mn, Ca or Mg
fixation
where is phosphorus deficiency a major problem?
in acidic tropical soils and some alkaline soils (when soil pH is either too low or too high)
what is the largest relative loss sizes? smallest?
largest: loss due to eroded particles
middle: loss due to runoff
smallest: loss due to leaching
due to the low solubility of P, it does not ________ across long distances easily and becomes depleted near roots and hyphae
diffuse
usually less than ______% of applied P is taken up by plants because of ______ solubility
30%
low
what are 3 things that we can do to increase P plant-availability?
-maintain pH at 6-7 (increases solubility)
-apply P near plant roots (decreases diffusion)
-add OM (blocks P sorption and precipitation)
what factors affect P availability?
-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)
what is the most common phosphorus mineral and fertilizer?
mineral: hydroxyapatite (in phosphorite rock “rock phosphate”) mined and found in bones
fertilizers: Ca(H2PO4)2, NH4H2PO4 or (NH4)2HPO4
there is also phosphorus in _________
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)
how does P pollution occur and why is P pollution harmful?
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)
what are the effects of P eutrophication?
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)
what are the 4 main sources of P in water?
-erosion
-waste
-fertilizer
-soaps and detergents
what are things we can do to control/limit P pollution?
-limit P application (to meet plant needs)
-reduce rates of soil erosion
-prevent waste leaks
-use P-free detergents
of the dry fraction, plants on average have ___-___% potassium (K)?
1-6%
what is the importance of K?
-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)
K loss from soil does not cause serious ____________ ____________
environmental issues
what are the soil K pools and how big are they?
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))
does K have a gas form?
no gas form (no atmospheric pool)
only solid and aqueous forms
what are potassium losses?
-erosion (only in exchangeable forms)
-runoff (soil solution)
-leaching (soil solution)
where are K-depleted soils found?
-places with increased precipitation (which causes increased erosion, runoff and leaching losses)
-lower pH/acidic soils = increased leaching due to more + charges
what factors affect K availability?
-faster soil weathering = greater K+ availability
-soil colloids (mica = lower K+ availability)
-more historical K+ fertilization = greater total K+ (management history)
if you over apply K, the K+ ions get __________ and they become fully unavailable
fixed
which soil orders has the least total K+? the most total K+?
least total K: oxisols and ultisols (highly weathered)
most total K: entisols (if soil is mica and feldspar rich)
most soluble (plant available) K: aridisols
what soil order has the greatest potential to fix K?
vertisols
when does a soil need K?
-sandy texture (causes high leaching)
-low pH (causes high leaching)
-high leaching
-high K removal during crop harvest
why do acidic soils need more K?
they have lower EAC which causes lower K+ sorption
why do alkaline soils need less K?
they have higher CEC which causes higher K+ sorption
how do we manage low K soils?
-small frequent K application (prevents trapping of K+ in interlayers)
-lime acidic soil (increases pH which increase negative change and increases CEC) (add calcite or dolomite)
-add organic soil amendments (increases CEC)
-K-efficient crops
both Ca and Mg are …
-secondary macronutrients
-alkaline earth metals
-base (nonacid) cations
what is the importance of Ca?
organisms in general:
-most organisms: electrolyte
-animals: bones and brain function
plants:
-cell wall component
-deficiencies are rare
-0.1-4% of dry plant weight
where are the unavailable Ca pools?
-Ca minerals (calcite, dolomite, and plagioclase feldspar)
-organisms and residues (plants, animals, and microbes) (soil organic matter)
where are the plant-available Ca pools?
-exchangeable (% saturation: 60-90% of cation exchange sites)
-soil solution
what is the general trend for most to least plant available?
(least) solid –> exchangeable –> solution (most)
what is the order of smallest to largest Ca pools?
(smallest) solution –> exchangeable –> solid (largest)
what are the important Ca and Mg additions (fluxes)?
-dust
-plant and animal residues
what are the important Ca and Mg transformations (fluxes)?
-uptake by organisms
-release from organism tissue
-precipitation and dissolution
-adsorption and desorption
what are the important Ca and Mg losses (fluxes)?
-erosion
-runoff
-leaching (sandy soils especially)
where are the Mg pools?
plant unavailable pools:
-minerals (dolomite, biotite, hornblede, and serpentine)
-organisms (oil + protein synthesis, enzyme activation, chlorophyll (in plants)
plant available pools:
-soil solution
-exchangeable (% saturation: 5-25% of cation exchange sites)
what is the smallest vs. largest pool?
soil solution = smallest
exchangeable = 2nd smallest
solid minerals = largest
what does Mg deficiency look like in plants?
yellowing of older leaves
why are Ca and Mg less likely to limit plant growth than K?
-Ca and Mg have a 2+ charge, so they have greater sorption strength to negative charge sites (compared to K+) which decreases leaching and decreases plant deficiencies
-Ca and Mg rich minerals are also more abundant in soils
-Ca and Mg don’t get trapped in the interlayers of clays like K+ does
in which pH are Ca and Mg likely to be deficient?
<5.5
why is silicon (metalloid) important?
-essential element for animals and humans
-taken up by all plants (quasi-essential, essential only for horsetails)
-interacts with cycling of many elements
-2nd most abundant element in earth’s curst after O
(common forms: SiO2, SiO4 4-)
what are Si pools?
-minerals (quartz, feldspar, phyllosilicates, non-crystalline silicates)
-soil solution (silicic acid: H4SiO4)
-plants and SOM (phytolith = Si deposit formed inside plants, phyto = plant, lith = rock)
is there atmospheric or gaseous pool of Si?
nope (dust is the closest answer)
what is a micronutrient?
nutrient required in amounts of <0.1% (<1g/kg)
most micronutrients are __________
cations–Fe, Mn, Cu, Zn, Ni, Co
(except Mo which is an anion)
there is a very narrow window of productivity for micronutrients, too low = _________, too high = ____________
deficiency
toxicity
which two pools flow directly to plants?
- ions in soil solution (smallest pool)
- chelates in soil solution
there is a small % of bioavailable micronutrients, due to what?
due to poor solubility and strong sorption (of transition metals)
micronutrients are more available when …
- soil pH is low
- in reduced form
- when chelated
(1st row transition metals) with a lower pH, there is less OH-, so _______ precipitation with OH- and a ____________ in solubility
less
increase
(1st row transition metals) with a higher pH, there is more OH=, so _________ precipitation with OH-, and a ____________ in solubility
more
decrease
reduced metals tend to be _____ soluble than oxidized forms
more
what is complexation?
when a nonmetal molecule binds to a metal
what is chelation?
type of complexation, where a nonmetal ion or molecule surrounds and binds to a metal at 2 or more points
what is a chelate?
soluble (usually organic) compound bound to a central metal at two or more points
anions are frequently soluble chelating agents which usually helps to ________ metals
dissolve
boron (occurs as boric acid: H3BO3) is very __________
soluble
(toxicity common in irrigated soils)
(easily leached)
because boron is very easily leached, is it the most commonly __________ micronutrient
deficient
(low concentrations esp in sandy and weathered soils)
molybdenum (form: molybdate anion: MoO4 2-) is ______ soluble at high pH
more (due to its negative charge, so it is repelled from negatively charged surfaces seen at high pH)
molybdenum competes with __________ for plant uptake… why?
sulfate (SO4 2-)
-due to similar chemical structure (tetrahedral shape)
-with an increase in sulfate, there is a higher chance for MoO4 2- deficiency
what is soil fertility?
ability of a soil to supply nutrients and provide favorable conditions for plant growth. therefore, a fertile soil: 1. retains and supplies essential plant nutrients in available chemical forms and in sufficient quantities to plant growth
2. maintains other physical and chemical properties favorable to plant growth
what are the general characteristics of a fertile soil? (think pH, weathering, CEC, etc…)
-medium weathering
-silt loam texture
-high PAW
-good drainage
-neutral pH (~6/6.5)
-high SOM
-high CEC
-low salts and sodium (EC < 4 and ESP < 15)
what are the main soil factors that affect plant nutrition?
-amount of nutrients in solid form
-weathering and mineralization rates
-amount of exchange sites (CEC, AEC)
what are the four main goals of nutrient management?
- cost effective production of high-quality plants and animals
- efficient use and conservation of nutrient resources
- maintenance or enhancement of soil health
- protection of the environment beyond the soil
what are the four R’s of nutrient management?
- right nutrient source (type of fertilizer)
- right nutrient rate (amount)
- right nutrient time
- right nutrient place
what is the law of minimum?
plant growth is constrained by the essential nutrient that is most limiting (typically nitrogen and phosphorus)
what are the 4 nutrient sources?
- soil minerals
- biological nitrogen fixation (rhizobia and actinomycetes)
- organic fertilizers
- inorganic fertilizers
organic non-synthetic fertilizers come from ________/_________ and contain ______
plants/animals
carbon
compared to synthetic fertilizers, non-synthetic fertilizers have ______ micronutrients and _____ macronutrients, and _____ organic C and _____ fertilizer “burn” risk
more
less
more
less
where do non-synthetic fertilizers come from?
- manure from confined animal feeding operations (CAFOs)
- sewage sludge (biosolids, municipal solid waste)
- sewage effluent (liquid waste water)
what three purposes does the addition of animal manure to soils serve?
- adds plant nutrients
- adds organic matter
- waste disposal
(dilutes organic nutrients: ~25-50% of N is available in the first year (less if composted))
what are the unique hazards of sewage sludge?
-heavy metals
-human pathogens
-emerging contaminants
liquid wastewater is valuable for __________, contains _________ nutrients and has similar concerns to sewage sludge
irrigation
dissolved
what are synthetic fertilizers?
inorganic (man-made) fertilizers and urea (come from haber-bosch processes)
what are the pros and cons of using non-synthetic organic fertilizers?
pros: adds OM to the soil, recycling resources, micronutrients and chelates, and minimal “burn” risk
cons: low nutrient content, pathogens, weeds and toxins, unpredictable nutrient release (organic fertilizers take time to be mineralized and become plant available, and mineralization rates are highly variable (depend on weather, soil properties, etc.)
Inorganic fertilizers are _______ to apply than non-synthetic organic fertilizers.
easier
inorganic fertilizers are generally _________ to plants right away.
available
what are the pros and cons of using synthetic fertilizers?
pros: known nutrient content, highly soluble, few impurities/no pathogens, predictable nutrient release, and inexpensive to transport
cons: produced with fossil fuels, does not add SOM to soil, narrow nutrient spectrum –> micronutrient deficiencies are more likely
what can be used to slow down the release of fertilizer nutrients?
“slow release” fertilizers
-slowly soluble materials
-organic amendments
-granules coated with resins or sulfur
describe fertilizer labeling mechanics
format is N-P-K
N = nitrogen
P = P2O5
K= K2O
fertilizer grade of 32-10-10 means what?
32% N
10% P2O5
10% K2O
how do you find the mass of each macronutrient from overall fertilizer?
- look up the atomic weights of elements
- multiply by subscripts
- add up elements to get total molecular weight
- divide nutrient element by total
how do you convert the mass of each element to the % of each element that the fertilizer contains?
- write out starting units and what units you want
- if P or K, then convert P –> P2O5 or K –> K20
- convert to fertilizer
- check that units cancel out to leave %
right rate: economics of fertilization
maximum profit occurs at ______ than maximum yield
less
right time: fertilize as close to the time of greatest crop ________ as possible
demand
the right place: what are the 3 fertilizer application methods?
broadcast: evenly distributed
banded: concentrated in a small area
foliar: sprayed directly onto plant leaves
right rate: how do u know if nutrients are needed?
-plant deficiency symptoms
-plant tissue tests
-soil tests
what is the purpose of soil sampling?
environment
-contaminant monitoring
-obtain data to model contaminant movement
agriculture/horticulture/rangeland
-determine if nutrients are above/below recommendations
-check for other growth limiting factors
what are three soil sampling methods?
- classical or random method
- grid method (suitable for precision farming)
- transect method (suitable for precision farming)
describe the classical soil sampling method
fields are divided into uniform areas and 15-25 samples are randomly collected within each area. areas may be based on:
-soil texture, slope, erosion, history, or productivity
what does the sample depth and time of sampling depend on?
sample depth depends on what you’re looking for.
time of sampling depends on analyses, field operations but are usually as close to planting as possible
describe the grid soil sampling method
samples are taken at pre-determined, evenly spaced intervals in x and y directions using GPS
describe the transect soil sampling method
samples are taken along a transect perpendicular to slope or expected variations in soil properties
how are soil samples tested in laboratories?
soil is weighed –> add solution –> shake –> filter –> measure
(most tests involve extracting nutrients with an aqueous solution and then analyzing them)
________ ___________ uses sensors in satellites to quantify soil properties remotely. Sensors can also be used on-site without sampling.
remote sensing
what is precision agriculture?
management of natural variability in soils and crops using monitoring and mapping technology (measure –> map –> manage)
-uses GPS and GIS
what is one way to decrease nutrient losses?
more plants –> decreased water flow (increased tortuosity) –> decreased runoff –> less nutrient loss
what are three techniques to slow down water flow?
3 techniques: buffer strips, contour strips and cover crops
what are the main benefits of riparian buffer strips?
-slows down water flow
-removes nutrients from water (prevents P and N pollution)
-degrades toxins
at what rate does a 10% contour strips (vegetation filters) help decrease nutrient loss?
89% less P and 82% less N are lost when there is a 10% contour strip coverage (prairie)
what is green manure?
cover crop terminated in-place (no harvest) to provide nutrients for the main crop (commonly legumes that naturally fix nitrogen)
what are cover crops?
plant grown in the off season to protect the soil from erosion
what do cover crops do for the soil?
cover crops conserves or add nutrients by reducing leaching losses and erosion along with adding organic matter
what does crop rotation do?
(switching crops between each year)
-reduces disease and pests –> nutrients used more efficiently
-rotating with legumes add biologically fixed n
-do not slow down water flow
what is soil degradation?
reduction in soil quality
-soil is non-renewable resource
how does soil degradation happen?
-erosion
-nutrient depletion
-organic matter depletion
-salt accumulation
-acidification
-compaction
what is erosion?
detachment and movement of soil or rock by water, wind, ice or gravity
-erosion destroys the most productive part of the soil (topsoil)
-excessive soil erosion has caused or contributed to the downfall of civilizations
____________ is the most widespread contaminant of surface waters
sediment
describe the positive feedback loop for soil quality
soil cover loss –> erosion –> soil degradation -> less plant growth –> soil cover loss
describe the upward spiral of restoration
more SOM –> better soil quality –> more plant growth –> less erosion
what are human activities causing soil degradation?
-overgrazing
-deforestation
-fuelwood gathering
-agriculture
describe the dust bowl and its causes
- climate and soil factors: semiarid climate, sandy soils, and high winds
- tillage and row cropping: prairie grasses were plowed under, wheat planted
- extended drought: 1933 to 1939
severe soil erosion by wind
what were responses to the dust bowl?
-creation of the Soil conservation Service
-11.3 million acres to kept out of production
-4 million acres of national grassland were created
what are the three types of soil erosion by water?
- sheet erosion
- rill erosion
- gully erosion
describe sheet erosion
-relatively uniform erosion from the entire soil
-causes the most erosion globally
describe rill erosion
-water concentrates in small channels (rills)
-cultivation/tillage may erase rills
describe gully erosion
-creates deep channels
-cannot be erased by cultivation/tillage
what types of erosion cause more soil erosion?
what types of erosion are wider and deeper?
sheet erosion causes the most soil erosion
gully erosion causes wider and deeper erosion
without vegetation, increased rainfall causes ________ erosion
increased
with vegetation, as rainfall increases, there is a sharp _________ in erosion and then a consistent __________
increase
decrease
wind erosion is most severe in _______ regions and in regions with _________ _______
arid
strong winds
more clay –> _________ aggregation –> less ____________ and –> ______ wind erosion
better
detachment
less
what soil textures are usually most erodible?
silt textures (medium texture sizes)
smaller particles = _________ travel distances
greater
-once particles are detached, clay particles travel further than larger particles
what does wind erosion result in?
particulate matter air pollution (PM)
-specifically PM 2.5
-different in composition than PM produced from fossil fuel combustion but still hazardous to respiratory health
what is tolerable soil loss (T value)?
maximum amount of soil that can be lost annually without degrading long-term productivity
(most soils have a t value between 5-11 Mg/ha/year)
(t values are used to evaluate compliance with environmental regulations but t values tend to be too high)
thicker A horizon = ________ t value
faster assumed soil formation rate = _________ t value
higher
higher
what are on-site impacts of soil erosion?
- decrease in soil quality
- loss of topsoil that is rich in organic matter, N, P, and biological activity
what are off-site impacts of soil erosion?
- sediment damage to waterways, aquatic life
- windblown dust – health and economic consequences
- nutrient contamination (N, P) of water (causes eutrophication)
what does the change in soil equal?
change in soil = [PM weathering] - [soil erosion losses]
what is the revised universal soil loss equation (RUSLE)?
A = R * K * LS * C * P
A = erosion loss in tons/acre/year or Mg/ha/year
what is R?
rainfall factor
higher total rainfall = higher R
greater intensity of rainfall = higher R
what is K?
soil erodibility factor
stronger aggregation = less detachment = lower K
clay has _________ aggregation = ______ K
sand has ___________ infiltration, __________ aggregation = _______ K
silt has ____________ infiltration, _________ aggregation = _________ K
greater, lower
increased, lower, medium
medium, lower, higher
what is LS?
length-slope factor (angle of slope and length of slope)
steeper slope = higher LS
longer slope = higher LS
what is C?
cover factor (= f (crop, tillage))
-more residues = _____ cover = _______ C
-more tillage = _______ cover = ________ C
more, lower
less, higher
what is P?
erosion control practices
-more effective practice = lower P = less erosion
-less effective practice = higher P = more erosion
(erosion control practices do not include those incorporated into the C factor (tillage and amount of residue left on soil)
how can you reduce the P factor?
- reduce attachment
-encourage soil aggregation
-protect the soil surface from rain and mechanical disturbances - reduce transport
-slowing down water and/or wind
what 4 things can decrease slope and slow down water flow in order to reduce erosion losses?
- terraces (stairstep like structures that slow down water flow by creating flat areas)
- contouring
- inter-row cropping
- strips of grass/trees
what is agroforestry?
growing crops among trees (trees protect crops from wind and water erosion, works well for shade tolerant crops)
what is contouring and how does it help reduce erosion?
plant crop rows and build terraces perpendicular to the flow of water
-helps plants intercept water –> slower flow –> less erosion
what are grassed waterways?
grass planted where water usually flows
-more grass –> slower water flow –> less erosion
what is strip cropping?
growth of alternating strips of annual row crops and full cover perennials (harvested at different times and both sold for $$)
what are contour strips?
dense grass shrubs or trees placed in curved formations perpendicular to water flow in a field to reduce the loss of nutrients, sediment and water
how can you control wind erosion?
- detachment is usually best controlled by practices that result in good soil cover and strong soil structure
- transport can be controlled by increasing vegetative cover and reducing field length by planting windbreaks
