Soils Test 3 Flashcards
essential plant nutrient
required for plants to live
minimum nutrients for survival
16 essential plant nutrients
C HOPKNS CaFe Mn B Mg CuZn Mo Cl
c hopkns cafe managed by my cousin mo clyde
primary nutrients
N, P, K
secondary nutrients
Ca, Mg, S
nutrients from water and atmosphere
C from atmospheric CO2
H and O from water
micronutrients
all others (Fe, Mn, B, Cu, Zn, Mo, Cl)
N ions
NO3- (anionic)
NH4+ (cation)
P ions
H2PO 4-
HPO4 2-
(both anionic)
K ions
K+ (cation)
Ca ions
Ca2+ (cation)
Mg ions
Mg2+ (cation)
S ions
SO4 2- (anionic)
4 mechanisms by which soil nutrients transfer from soil to plants
mass flow-sucked up through water
root interception-roots in contact with nutrient
ion exchange on colloidal regions
simple diffusion-random movement
Importance of N to crop yields
number one primary nutrient needed in plants
easiest of the nutrients that can be lost
increases crop yields
most limiting for plant growth
3 main functions of N in plants
component of chlorophyll for photosynthesis
component of nucleic acids which form DNA, RNA
essential element of all amino acids
Healthy plants contain how much N
2.5-4%
Deficiency symptoms of N and S
leaves pale yellowish green in color
5 inputs of N into plant root zone
biological N2 fixation (legumes) industrial fixation (N fertilizers) lightning oxidation (N2 to NO3-) organic matter decomposition animal wastes
5 losses of N from the root zone of crops
crop removal NH3 volitilization denitrification leaching physical removal (erosion, land grading, etc)
N mineralization
converting organic nitrogen from organic matter into inorganic nitrogen (ammonia or ammonium) due to microbial activity
N immobilization
converting inorganic nitrogen into organic. (opposite mineralization)
SON
soluble organic nitrogen
new findings
nobody really knows the makeup of this yet
Ammonium fixation by clay minerals
layers of clay swell when hydrated. Ammonium can drift in between layers and when the clay drys it is stuck between
Ammonium volatilization
the release of ammonium into the atmosphere. nitrogen is lost as ammonia gas
3 factors affecting ammonium volatilization
pH
CEC
H2O
N mineralization
3 major N reactions in soil
mineralization
nitrification
denitrification
Nitrification
oxidation of ammonium by bacteria
Step 1: NH4+ –> NO2- gas
Step 2: NO2- –> NO3-
5 factors affecting nitrification
pH CEC H2O temperature microorganisms
Denitrification
bacteria convert NO3- to N2 gas
sucks all the oxygen out of nitrates
General class of soil organisms responsible for denitrification
facultative anaerobic bacteria
5 factors affecting denitrification
pH CEC H2O temperature oxygen
Why are soil tests for N a poor indication of fertilizer needs
because of the mobility of nitrates in soils and the complex transformations of nitrogen from soil organic matter
What leaches through soil with a high CEC faster NO3- or NH4+
NO3-
What is urease
soil enzyme that breaks down urea in releasing NH4+.
increases mineralization of N in urea
Why is ammonium nitrate a better fertilizer to apply to unirrigated turfs and pastures than urea in the summer
because urea tends to be lost to the air when left for extended periods of time in warm weather.
irrigation will help blend urea into soil
no special management considerations for ammonium nitrate
When is a good time to apply urea to turfs and pastures
just before rain or irrigation
also works well if tilled into the soil
Why is urea a better N source in flooded rice fields than ammonium nitrate
because it won’t be denitrificated
Biological N2 fixation reaction
N2 + 8 H+ + 8 e− → 2 NH3 + H2
atmospheric nitrogen converted to ammonia by nitrogenase
Nitrogenase
protein enzymes used to fix atmospheric nitrogen gas
4 facts about nitrogenase
needs O2
needs Fe, Mo
needs living organisms (mostly rhizobrium & bradyrhizobium)
influenced by the environment (O2, temp, pH)
4 N fixing organisms
rhizobium spirillum cyanobacteria clostridium azotobacter
Practical N managment in ag and hort soils
soil pH improve soil organic matter don't let other nutrients get deficient set realistic yield goals don't over fertilize N apply in increments use urea in rice use stabilized urea (urease inhibitors) in other crops keep fields from ponding inocculate legume seeds
Function of S in plants
structural component of various enzymes
constituent of amino acids
synthesis of oils
3 major natural sources of S in soils
organic matter
soil minerals
atmosphere
Organic S in soils compromise how much of total S in root zones
.15-.45%
S mineralization
organic S forms are transformed into inorganic
organic S –> decomposition –> SO4 2- mineralization
S immobilization
opposite of mineralization
transforms inorganic S into organic S
SO4 2- –> organic S
S fixation
SO4 2- –> mineral like CaSO4
Role of P in plants
ATP
RNA
DNA
In healthy plants P makes up how much of tissue dry matter
.2-.4%
General deficiency symptoms of P
stunted plant (short stocky) dark or blueish green in color
3 sources of P input
fertilizer
minerals
organic matter
3 sources of P output
erosion
plant uptake
water runoff
Is P a very mobile nutrient in soil systems?
No, its through root interception
2 broad classifications of P in soils
organic
nonorganic
Effect of mycorrhizae fungi on P uptake by plants
increase volume in the soil
P eutrophication
a high concentration of P in a body of water causes excessive algae growth
Main source of dissolved organic P in soils
animal waste
How does the mobility of Dissolved Organic P (DOP) compare to inorganic sources of P
has a higher mobility
optimum pH for P availability
6.5
Fixation of P in acidic soils mostly with
Al, Fe, Mn
Fixation of P in alkaline soils mostly with
Ca
Compound that can remove soluble phosphates from sewage treatment water or animal wastes
Aluminum
P fixation capacity of the soil
ability of a soil to fix P from available to unavailable
H2PO4–> CaHO4
3 factors affect P fixation
pH
organic matter
clay content
Role of K in plants
non-structural
water regulation through opening and closing of stomates
enzyme activation
In healthy plants K makes up how much of tissue
1-4%
Deficiency symptoms of K
fixing of leaf margins (usually older leaves)
Luxury consumption
uptake of excessive nutrients beyond whats needed but with not adverse effects
four states of K
solution
exchangeable
mineral component
fixed between sheets of some 2:1 layer silicate clays
2 examples of popular K fertilizers
muriate of potash (0-0-60) KCl
sulfate of potash (0-0-50) K2SO4
Role of Ca in plants
cell wall support
fruit development
3 states of Ca in soils
exchangeable Ca (available) mineral Ca (unavailable) complex with soil humus (unavailable)
Relationship of Ca availability and soil % base saturation
B.S. goes up, Ca2+ goes up
3 main losses of Ca (and Mg) from soils
leaching
crop removal
erosion
Role of Mg in plants
chlorophyll
photosynthesis
Preferred Ca/Mg range in soils
1:1 to 15:1
Soil conditions where micronutrients may be deficient
acidic or alkaline organic intensively cropped eroded/shallow sandy/leached derived from some parent materials
chelated micronutrient
cation micronutrient encapsulated by large organic molecules
ex: Zn-EDTA, Cu-EDTA, Fe-EDTA
Zn role in plants
several, seed production and hormone constituent
Fe role in plants
Redox reactions, respiration, energy, ATP production
Cu role in plants
photosynthesis, protein synthesis
Mn role in plants
N metabolism, assimilation
Co role in plants
N fixation, vitamin B12
B role in plants
cell division and growth
Mo role in plants
N fixation by legumes
