Midterm Study Guide Flashcards
How was soil fertility managed during the Neolithic?
Slash and burn
What fertility theory dominated the Middle Ages?
Humus theory
What characterizes Humus Theory?
The idea that plants “eat” soil particles.
How does the practice of tillage relate to Humus Theory?
It was believed that finer soil particles facilitated plant root ingestion of soil for fertility.
What fertility theory arose in the 19th century?
Mineral plant nutrition; NPK
Who discovered that plant carbon comes from the atmosphere, not soil?
Justus von Liebig
Who discovered N-fixation?
Hellriegel and Wilfarth
Approximately half the yield increases from the Green Revolution were from _____.
Fertilization
Fertilizer use efficiency is generally ____% or less.
40
Sustainable agriculture is related to alternative/organic agriculture. (T/F)
F
Sustainable approaches can be incorporated into any agricultural system. (T/F)
T
Sustainability of a farming system is only marginally related to fertilizer (organic/inorganic) or other inputs. (T/F)
T
Intrinsic soil factors, rainfall or irrigation practices, and management related factors have a greater influence on farm sustainability than soil amendments or other inputs. (T/F)
T
What legislation provided for land-grant state colleges and universities for agriculture and mechanical arts?
Morrill Act 1862
What legislation gave federal land grants to states in order to create a series of agricultural experiment stations to study soil minerals and plant growth?
Hatch Act 1887
What legislation assisted states in carrying on a program of forestry research and for purposes of developing/utilizing resources from forests and related rangelands?
McIntire-Stennis Act 1962
Major agricultural research drivers in the last century:
-Food supply and safety
-Land expansion
-Population growth
-Limitations on renewable resource availability
-Maintaining productivity
Most funding for research now comes from the ____ sector.
Private
The relationship between essential nutrient concentration and plant growth:
As nutrient concentration increases towards critical range, plant yield increases. Above the critical range, the plant contains sufficient levels for normal growth and can continue to absorb nutrients without increasing yield (luxury consumption). Excessive absorption can be toxic and reduce yield.
The technological innovation that provides inorganic nitrogen for fertilizers.
The Haber-Bosch process
What factors of precipitation affect plant growth?
Quantity and distribution
What is the thesis of the Malthusian Population Trap?
Population expands geometrically, food production increases arithmetically
What is Liebig’s Law of the Minimum?
Plant yield is directly related to the minimum or limiting nutrient; yield will not increase if more nutrients other than the limiting one are added.
What are micronutrients?
Nutrients required in smaller amounts and may only be required by certain plants.
What are the essential macronutrients?
NPK, Mg, Ca, and S (also C, O, and H)
What are the essential micronutrients?
B, Cl, Mn, Fe, Ni, Cu, Zn, and Mo
Mg is a (macro/micro) nutrient.
Macro
Ca is a (macro/micro) nutrient.
Macro
S is a (macro/micro) nutrient
Macro
Fe is a (macro/micro) nutrient.
Micro
P is a (mobile/nonmobile) nutrient.
Mobile
Mg is a (mobile/nonmobile) nutrient.
Mobile
Cl is a (mobile/nonmobile) nutrient.
Mobile
Mo is a (mobile/nonmobile) nutrient.
Mobile
K is a (mobile/nonmobile) nutrient.
Mobile
N is a (mobile/nonmobile) nutrient.
Mobile
Ni is a (mobile/nonmobile) nutrient.
Nonmobile
Zn is a (mobile/nonmobile) nutrient.
Nonmobile
B is a (mobile/nonmobile) nutrient.
Nonmobile
Fe is a (mobile/nonmobile) nutrient.
Nonmobile
Ca is a (mobile/nonmobile) nutrient.
Nonmobile
Mn is a (mobile/nonmobile) nutrient.
Nonmobile
S is a (mobile/nonmobile) nutrient.
Nonmobile
Cu is a (mobile/nonmobile) nutrient.
Nonmobile
What are the general plant symptoms of mobile nutrient deficiencies?
Older leaves will display deficiency symptoms before younger leaves.
What are the general symptoms of immobile nutrient deficiencies?
Younger leaves will display deficiency symptoms first, and symptoms may be localized.
The most concentrated nutrients in plants are ___ and ___.
O and C (about 45% each)
H concentrations in plants are ____%
6
N concentrations in plants are ___%.
1.5
K concentrations in plants are ___%.
1
P concentrations in plants are ___%.
0.2
Ca concentrations in plants are ___%.
0.5
Mg concentrations in plants are ___%.
0.2
S concentrations in plants are ___%.
0.2
Micronutrient concentrations in plants are less than or equal to ___%.
0.01
Macronutrient concentrations in plants are greater than or equal to ___%.
0.2
What is the Steenberg effect?
A rapid yield increase with added nutrients can cause a small decrease in nutrient concentrations in the plant.
What are essential plant nutrients?
Mineral elements required for plant growth and development
The criterial for essential elements:
-Required for growth and reproduction
-Specific (can’t be replaced)
-Acts directly
Silica is an essential nutrient (T/F).
F (beneficial)
Na is an essential nutrient (T/F).
F (beneficial)
Co is an essential nutrient (T/F).
F ( beneficial)
Se is an essential nutrient (T/F).
F (beneficial)
B is an essential nutrient (T/F).
T
Cl is an essential nutrient (T/F).
T
Mn is an essential nutrient (T/F).
T
Fe is an essential nutrient (T/F).
T
Ni is an essential nutrient (T/F).
T
Cu is an essential nutrient (T/F).
T
Zn is an essential nutrient (T/F).
T
Mo is an essential nutrient (T/F).
T
In the inorganic components of soil, (primary/secondary) minerals provide the greatest ion exchange capacity.
Secondary
How to minerals contribute to nutrient availability?
Ion exchange; weathering.
The hydrolysis of feldspar yields ____.
Kaolinite
The oxidation of biotite yields ____.
Iron oxides
The hydrolysis of biotite yields ____.
Vermiculite
How is CEC defined?
meq/100g soil
1meq/100g = __ cmol/kg
1
Equivalent weight =
grams/equivalent
For a monovalent ion, equivalent weight =
Atomic weight
For a divalent ion, equivalent weight =
1/2 atomic weight
How does pH affect CEC?
Low pH decreases; high pH increases
(1:1/2:1) clays are non-expanding.
1:1
(1:1/2:1) clays are pH dependent.
1:1
(1:1/2:1) clays are low CEC.
1:1
(1:1/2:1) clays are non-sticky.
1:1
(1:1/2:1) clays are expanding.
2:1
(1:1/2:1) clays are constant charge.
2:1
(1:1/2:1) clays are high CEC.
2:1
(1:1/2:1) clays are sticky.
2:1
(1:1/2:1) clays are low surface area.
1:1
(1:1/2:1) clays are high surface area.
2:1
What is the source of permanent charges in clays?
Isomorphous substitution
What is isomorphous substitution?
Substitution of the central atom of a clay sheet with a similarly sized atom.
What soil particles have mainly pH dependent charge?
1:1 clays, OM, oxides.
How is CEC estimated?
The sum of: (CEC x percent composition) of the constituents.
How is CEC determined in the lab?
NH4 used to replace all other cations on exchange complex, ethanol rinse to remove excess, then Ba2Cl OR KCl used to extract NH4 ions. Filtrate analyzed to determine CEC.
ppm =
mg/L
How do clay type and SOM influence buffering capacity?
Higher CEC –> higher buffering capacity
What is buffering capacity?
The ability to resupply nutrients to soil solution.
CEC: OM (>/<) clay
>
Base saturation is defined as:
% of CEC occupied by Ca, Mg, K and Na.
How does base saturation affect soil pH?
Higher base saturation –> less acid cations –> higher soil pH
Do plants have ion exchange properties?
Yes, the roots.
Monocots have (higher/lower) plant root CEC.
Lower
Dicots have (higher/lower) plant root CEC.
Higher
Why have dicots evolved more CEC?
Roots have less surface area; must compensate to remain competitive.
Lyotropic series:
Al>H>Ca>Mg>K=N>Na
Adsorption strength of an ion depends on ____ and ____.
Valence and hydrated radius size.
Greater valence —> _____ adsorption strength.
Greater
Greater hydrated radius size –> ____ adsorption strength.
Weaker
Anion lyotropic series:
PO4>SO4>NO3
(Sandy/clay) soils require higher rates of fertilizer application to maintain the same solution concentration.
Clay
How does soil water content affect the solubility of minerals?
Less water —> more precipitation/less solubility
How are nutrients within SOM released?
Mineralization by microorganisms.
C/N/P/S =
100/10/1/1
What is the difference between mass flow and diffusion?
Mass flow occurs by evapotranspiration, while diffusion occurs by movement along a concentration gradient.
How do dry soil, low soil temperatures, and hot afternoons affect mass flow?
Reduces transpiration –> reduces mass flow
Finer textured soils have a (lower/higher) effective diffusion coefficient.
Higher
At a given level of saturation, (1:1/2:1) clays will supply more of a nutrient.
1:1
High CEC –> (more/less) diffusion
Less
What mainly determines the mobility of a nutrient in the soil solution?
Quantity in soil solution in relation to quantity needed by crop.
Nutrient mobility (increases/decreases) as nutrient deficiency increases.
Decreases
SO4 has ___ mobility in the soil solution.
High
Cl has ___ mobility in the soil solution.
High
NO3 has ___ mobility in the soil solution.
High
Na has ___ mobility in the soil solution.
High
Ca has ___ mobility in the soil solution.
Intermediate
Mg has ___ mobility in the soil solution.
Intermediate
K has ___ mobility in the soil solution.
Intermediate
NH4 has ___ mobility in the soil solution.
Intermediate
MoO4 has ___ mobility in the soil solution.
Low
PO4 has ___ mobility in the soil solution.
Low
Micronutrient metals have ___ mobility in the soil solution.
Low
Why do some cations that adsorb strongly to the CEC move primarily by mass flow?
High prevalence on CEC causes constant exchange, increasing concentration in soil solution
(Mobile/Immobile) [in soil] nutrients have larger zones of depletion.
Mobile
(Mobile/Immobile) [in soil] nutrients have stronger sorption on soil colloids.
Immobile
(Mobile/Immobile) [in soil] nutrients have larger soil reserves.
Immobile
(Mobile/Immobile) [in soil] nutrients have higher buffering capacity.
Immobile.
(Mobile/Immobile) [in soil] nutrients have higher availability to plants.
Mobile
(Mobile/Immobile) [in soil] nutrients have greater accumulation at soil surface.
Immobile
(Mobile/Immobile) [in soil] nutrients have greater leachability.
Mobile
(Mobile/Immobile) [in soil] nutrients have greater short-term crop recovery.
Mobile
(Mobile/Immobile) [in soil] nutrients have greater competition between plants.
Mobile
Mobile
Immobile
Mobile
Immobile
Immobile
What is the difference between passive and active nutrient uptake by roots?
Cell must use energy to use active uptake.
How do different types of clay supply nutrients to the soil solution differently?
1:1 clays will supply more of a nutrient at a given level of saturation.
Nutrient mobility (increases/decreases) as a nutrient deficiency (in the plant) increases.
Decreases
Diffusion is a type of (active/passive) cellular transport.
Passive
Facilitated diffusion is a type of (active/passive) cellular transport.
Passive (What about transporter proteins?? Active!)
Apoplastic pathways are (actively/passively) driven.
Passively
The drivers of apoplastic pathways:
-Diffusion
-Capillary action
-Osmosis
In apoplastic pathways, nutrient selection occurs at the ______, and unselected nutrients are deposited in the _____.
Casparian strip; cortex
Symplastic pathways are (actively/passively) driven.
Passively
Symplastic pathways include transportation by ____ and _____.
Plasmodesmata; xylem
What is a uniporter?
A transporter protein that moves one molecule at a time down an electrochemical gradient.
What are symporter proteins?
A transporter protein that catalyzes movement of a molecule against its electrochemical gradient by coupling it movement with an oppositely charged molecule moving down its gradient in the same direction.
What is an antiporter?
A transporter protein that a catalyzes movement of a molecule against its electrochemical gradient by coupling its movement with a similarly charged molecule moving down its chemical gradient in the opposite direction.
What is the relationship between nutrient concentration in solution and the rate of nutrient passive uptake?
Slow, linear increase in uptake with increasing concentration.
What is the relationship between nutrient concentration in solution and the rate of nutrient active uptake?
Sharp increase with initial increase in concentration, leveling out at maximal rate of uptake (Vmax).
Water and ions move into epidermal and cortical cells via (apoplastic/symplastic) pathways.
Apoplastic
Ions cross the Casparian strip via (active/passive) transportation.
Active.
What nutrient do mycorrhizae primarily help to absorb?
Phosphorous
How does nutrient uptake affect pH?
Uptake of cations is facilitated by the release of another cation, usually a proton. Uptake of anions is facilitated by the release of another anion, usually a hydroxyl.
What is the liming equation?
CaCO3 + H –> Ca + CO2 +H2O
What is the site of nutrient uptake in plant roots?
The apoplastic pathway.
What is the site of nutrient selection in plant roots?
The Casparian strip
What is the pH of a solution in equilibrium with the atmosphere?
5.65
Kw=
10^-14
pK:
the pH at which an acid is 50% dissociated
pH in a buffered system =
pK + log([A-]/[HA])
The nitrification equation:
NH4 + 2O2 <–> NO3 + H2O +2H
How do clays, oxides, and SOM contribute to pH buffering?
Dissociation of exterior protons.
How can soluble salts contribute to acidification?
Base cations can displace acid cations on the exchange complex.
Potential acidity includes ___ and ___.
Exchangeable acidity and titratable acidity.
What is titratable acidity?
H and Al that are bound to the exchange complex, not in their ionic state.
The equivalent weight of pure calcium carbonate =
50g/Eq
How is base saturation related to pH?
Base saturation increases with pH
How does liming affect Al and Mn toxicity?
Reduces. Both are highly soluble at low pH.
Why do rice fields rarely require liming?
Anaerobic processes consume protons.
What are the most common methods of acidifying alkaline soils?
Elemental sulfur and sulfuric acid.
How does sulfur acidify soil (reaction)?
2S + 3O2 +2H2O <–> 2SO4 +4H
How is phosphate availability affected by pH?
Fixes to Fe and Al at low pH and Ca at high pH
How is N availability affected by pH?
Low pH inhibits N fixation (most effective above 6.0).
What effect does sodium have on soil structure?
Dispersion between Na ions on exchange complex causes dispersion of colloids, destroying structure.
EC of saline soils:
> 4mmho/cm
pH of saline soils:
<8.5
ESP of saline soils:
<15%
EC of sodic soils:
<4mmho/cm
pH of sodic soils:
> 8.5
ESP of sodic soils:
> 15%
EC of saline-sodic soils:
> 4mmho/cm
pH of saline-sodic soils:
pH<8.5
ESP of saline-sodic soils:
> 15%
How does sodium in sodic soils result in high pH?
Water molecules split to produce protons in solution that preferentially displace sodium, producing hydroxyls.
SAR =
Na/sqrt[(Ca+Mg)/2]
ESR =
Na/(Ca+Mg)
Relationship between SAR and ESR
ESR= 0.015(SAR)
Relationship between ESP and ESR
ESP= (100 ESR)/(1+ESR)
How does sodicity affect infiltration?
Colloids disperse, destroying structure and reducing permeability.
Crops in nutrient-(poor/rich) soils are more salt tolerant.
Poor. Slower growth.
Why is clean water unsuitable to leach a sodic soil?
There is nothing to displace Na on the exchange complex.
