Midterm 2 Flashcards
P mineralization is most effective in soils with pH (</>) 7.
<7
(Ammonium/nitrate) inhibits phosphate uptake.
Nitrate.
C;N cutoff between organic and synthetic fertilizers.
2:1
Step two of N mineralization:
Ammonification
The main P minerals in acid and neutral soils.
Al/Fe phosphates
SOM contains about ____% N.
5%
What is the function of S in proteins?
Protein folding.
(More/less) weathered soils adsorb sulfate more strongly.
More
S mineralization is (positively/negatively) correlated with the abundance of plants.
Positively.
In plants, Mg is (mobile/immobile).
Mobile
In plants, Ca is (mobile/immobile).
Immobile
Step one of N mineralization:
Aminization
In soils, K is (mobile/immobile).
Mobile.
Where is most S in plants found?
Amino acids; ~90%
Under what soil conditions would band placement of P result in the greatest utilization by the plant?
Highly buffered soils; banding prevents interactions.
P mineralization occurs at a C:P <____:1.
200
What is the difference between single and triple superphosphate?
Triple is acidified with sulfuric acid, has less impurities. Single is acidified with phosphoric acid, has more impurities.
S immobilization occurs at a C:S >____:1.
400
In legume, N fixation generally accounts for between ____% and ____% of N requirements.
50-75%
The most important P fertilizer.
Acid treatment P fertilizer: rock phosphate
Sulfate adsorption is increased at (low/high) pH.
Low
When pH is lower than 5.5-6, N fixation (increases/decreases).
Decreases.
What effect does liming have on K uptake?
Ca displaces Al and H, freeing up exchange sites for K. Ca displaces K, improving absorption from solution.
Highly weathered soils (maximize/minimize) P sorption.
Maximize; strongly adsorbed to oxides.
The first step of nitrification is carried out by ______.
Nitrosomonas
(Singe/triple) superphosphate can cause S deficiencies.
Triple; less impurities
S mineralization is (increased/decreased) temperatures below 10C.
Decreased
What major differences mark the S cycle in comparison to the N cycle?
No S fixation, nitrification, etc…
Anion adsorption is increased when ____ cations are on exchange sites.
Divalent
The main P minerals in alkaline and calcareous soils.
Calcium phosphates
What is the biggest difference between symbiotic and associative N fixation?
Symbiotic N fixation is endophytic (occurring within the plant roots), while associative occurs in the rhizosphere.
N influence on carbohydrate activity:
(High/low) N causes proteins to be formed from carbohydrates, resulting in a more succulent plant.
High
Input (quality/quantity) is more important for N availability.
Quality
Organic P is concentrated in which soil horizon?
A
Why are phosphates used to extract sulfate?
Phosphate has a stronger adsorption strength.
The optimal pH for nitrification:
8
How does pH affect the form of ammonical N?
High pH, more ammonia
The second step of nitrification is carried out by _____.
Nitrobacter
At a given level of saturation, (1:1/2:1) clays will supply more Ca.
1:1; buffering capacity
At what pH is P availability maximized.
6.5
In plants, S is (mobile/immobile).
Mobile
N fixation (increases/decreases) soil pH.
Decreases
How does the K cycle differ from micronutrient cycles?
K fixation
The enzyme complex responsible for N fixation.
Nitrogenase
K in organic residues occur mainly as _____.
Soluble inorganic K.
____ is the principle dry N source in the world.
Urea
Ammonium fixation can occur in ____ clays.
2:1
At low pH. P precipitates with ____.
Fe and Al.
In soils, Ca is (mobile/immobile).
Immobile
______ fix N in symbiosis with nonlegume trees.
Frankia
Sulfate (is/is not) easily leached from soil.
Is
(T/F) P in soil is lost mainly by leaching.
False; erosion
The main pool for soluble P in soil.
SOM
How does liming an acid soil affect K availability?
Displaces H and Al from CEC, freeing up sites for K.
T/F: Plants can selectively uptake Ca vs. Mg.
False; both move by mass flow and are divalent; Casparian strip cannot differentiate.
Adsorption of sulfate is increased in (topsoil/subsoil).
Subsoil; more oxides and clay
(1:1/2:1) clays generally have more K.
2:1; buffering capacity
What P fertilizer is often used as a starter fertilizer?
Ammonium phosphates
Most ammonium in soil is nitrified within ____ weeks.
3
In plants, N is (mobile/immobile).
Mobile
N influence on carbohydrate activity:
(High/low) N causes carbohydrates to deposit in the vegetative cells, causing them to thicken.
Low
What pools of SOM is most important to plant nutrition?
The light fraction; active fraction; labile SOM
At high pH. P precipitates with ____.
Ca
At a given level of Ca saturation, (high/low) CEC soils will have greater Ca absorption by plants.
Low; buffering capacity
What is the added nitrogen interaction?
When N fertilizer is applied, less than one half is directly absorbed by plants. Regardless, N uptake roughly equals the amount supplied. This is because microbes uptake the additional fertilizer N, causing them to consume SOC, subsequently releasing SON.
Denitrification (increases/decreases) under anaerobic conditions.
Increases.
(Excessive/deficient) N causes excessive succulence, enhancing diseases, insect damage, and lodging susceptibility.
Excessive
S mineralization is (positively/negatively) correlated to soil moisture content.
Negatively; concentration
Calcium uptake is impeded at (low/high) pH.
Low; H and Al impede uptake
The effect of other cations on Ca uptake.
Depressed by other cations.
In soils, S is (mobile/immobile).
Mobile (except very acid soils).
Weathering of parent material generally (increases/decreases) the K content of minerals.
Decreases
How does Ca on the CEC affect K absorption?
Ca displaces K on CEC.
In plants, P is (mobile/immobile).
Mobile.
How does pH affect K availability?
Low pH reduces K on CEC.
In soil, P is (mobile/immobile).
Immobile
What is the most commonly used dry Mg fertilizer?
Epsom salts.
At low pH, what ions impede K uptake?
Al and Mn
How do divalent cations on the CEC affect P sorption?
Increase
In soils, Mg is (mobile/immobile).
Mobile
In soil, NO3 is (mobile/immobile).
Mobile
Typical N2:N2O produced via denitrification:
11:1
In plants, K is (mobile/immobile).
Mobile.
What cation has the greatest potential to leach with nitrate?
K
How does the biological component of the P cycle compare to the N cycle?
Similar
(Ammonium/nitrate) improves phosphate uptake.
Ammonium
What major nutrient enhances P uptake?
NH4; increased growth.
What effect does gypsum have on K uptake?
Ca displaces K on CEC, resulting in higher [K] in solution (more absorption).
Ca uptake is (increased/decreased) in the presence of nitrate.
Increased.
What extractants are mainly used for sulfate?
Calcium dihydrogen phosphate and potassium dihydrogen phosphate.
Organic N accounts for ____% of total N in soil.
95%
___% of reactive N produced in Haber-Bosch process and used for animal production enters the human mouth.
4%
At high pH, what nutrients compete with K for uptake?
Ca and Mg.
What is the substrate of nitrification?
Ammonia!
Between ____% and ____% of organic N in mineralized in a growing season.
1-4%
Naturally occurring P in soils originates from _____.
Parent material
S mineralization is (positively/negatively) correlated to soil pH.
Negatively
K is mainly derived from ____.
Parent material
What is the major difference between the P cycle and N cycle?
The abiotic component of the P cycle is highly pH dependent.
Sorption of P is stronger in (1:1/2:1) clays.
1:1
The functions of K are largely related to its ____.
Ionic nature; ionic strength of solution in plant cells.
Soil carbon storage is maximized under (warm/cool) and (moist/dry) conditions.
Cool and moist
Ca saturation (increases/decreases) K absorption from soil solution.
Increases.
Tissue K content is (positively/negatively) correlated to transpiration.
Negatively.
What is the largest pool of soil S?
SOM
Nitrification is (more/less) efficient at low pH.
Less
P immobilization occurs at a C:P>____:1.
300
K uptake is (greater/less) than Mg uptake.
Greater
Where is S mainly derived from?
Volcanism.
K uptake is (positively/negatively) correlated with temperature.
Positively
The enzyme responsible for mineralization of organic P.
Phosphatase
Input (quality/quantity) is more important for SOC accumulation.
Quantity
What is the dominant pool of S in soils.
Organic; 94-95%
Nitrification is more efficient at (high/low) pH.
High; more ammonia, less ammonium
Nitrification inhibitors are (more/less) effective than micro-irrigation.
Less
What is the largest pool of soil N?
SOM.
Tissue K content is (positively/negatively) correlated to CO2 assimilation.
Positively.
What is the common K extractant used for arid soil, such as in California?
Nitric acid; used for fixed K.
What microorganisms are responsible for S oxidation?
Sulfur oxidizing bacteria (mostly aerobic).
(T/F) Anthropogenic reactive N production is greater than natural production.
True
(1:1/2:1) clays more strongly adsorb sulfate.
1:1
Calcium deficiencies are (common/rare).
Rare
Is symbiotic or associative N fixation more effective?
Symbiotic
The main form of S that is available to plants.
Sulfate.
What environmental factors affect S oxidation?
Temperature (25-40 C), moisture/aeration (goldilocks zone), and soil pH (wide range, but some microbial species like very low pH).
Approximately 50% of N-fixation is carried out by _____.
Rhizobia
In soil, NH4 is (mobile/immobile).
Immobile
C:N:P:S in SOM.
100:10:1:1
What is grass tetany?
Magnesium deficiency in ruminants.
S mineralization occurs at a C:S <____:1.
200
