Nutrients Flashcards
What are the ultimate sources of N?
biological, industrial, lightning
What are the on farm sources of N?
biological fixation by crop, SOM, crop residue, manure, inorganic fertilizer
What are the plant available forms of N?
NH4+ (ammonium)
NO3- (nitrate)
some plants favor one source over another
What are the major processes for N?
mineralization
nitrification
What is mineralization of N?
converting organic N to inorganic N biological process broken down by microbes (aerobic) approx. rate of 1.5-3.5% of organic soil N/yr reaction requires water
What does the rate of N mineralization depend on?
temperature, moisture, aeration
limited by low temperatures
enhanced by substrate for the bacteria
What is immobilization of N?
converting inorganic N to organic forms
occurs simultaneously with mineralization
net effect is determined by C:N ratio in organic residues
microbes need N too
What is ammonium fixation in clay minerals?
positive ion attracted to clay’s negative ions
available for plant uptake, but partially protected from leaching
can become entrapped in cavities
usually greater in subsoil
What is ammonia volatilization?
ammonia gas lost from soil
more pronounced as pH increases
incorporating amendments can help reduce loss to volatilization
What is nitrification?
bacterial oxidation of ammonium (biological)
necessary to make N available for plant uptake
2 step reaction - nitrosomonas, nitrobacteria
significantly increases soil acidity
How can inorganic N be lost?
volatilization, many ways
What is immobilization enhanced by?
incorporating high C residues
manure w/lots of bedding
adding materials with C:N ratios >30
What conditions increase volatilization?
warm temperatures, steady winds, high pH soils, using an N source that is volatile, not incorporation manure/fertilizer
What conditions increase denitrification?
warm temperatures, time, lots of microbial activity, saturated or near saturated conditions
What is N20?
nitrous oxide
major greenhouse gas
a lot contributed by ag
NPS
How does fertilizer N work?
can be nitrate or ammonium
immediately available when it goes into solution
rapidly available
high energy costs
several forms available - urea, ammonium nitrate, ammonium sulfate, AA, etc.
no guesswork like other options
can cause soil acidification (lime)
What is the problem with nitrate?
it’s very mobile, can move down and laterally
major source of NPS pollution
How can soil N contribution be estimated?
in many situations, this is the biggest single N source
it’s hard to predict
no widely accepted test for estimating SOM mineralization (crucial problem)
What are sources of N?
soil N
fertilizer (Haber-Bosch)
legume fixation
What is the Haber-Bosch process?
get H to synthesize ammonia from atmospheric N
energy intensive process
major improvements in efficiency
What are the consequences of Haber-Bosch?
water and air pollution
loss of biodiversity
increased greenhouse gases
increases soil acidification
lots of N lost - cascades to N-limited ecosystems
eutrophication
What are the ultimate sources of P?
soil parent materials, mined inputs, excretion, guano, phosphate rock
What are the on farm sources of P?
SOM, soil mineral fraction, crop residue, manure, inorganic fertilizer
What is the plant available form of P?
generally H2PO4-
What are the major processes for P?
mineralization
immobilization
What are problems with P?
it’s efficiency is very low
small ratio of applied is actually available
high Al and Fe or low pH make this worse
N based manure application generally over applies P (poultry manure)
erosion moves P to surface water
What is the problem with surface application of manure?
high potential for movement in run-off, move to surface water
How does P change forms?
total soil P –> solution P –> land
solution P is very small pool relative to total
plant can only use solution pool
What is soil P saturation?
ratio of extracted P to extracted Al and Fe
point that Al and Fe aren’t effective at binding P
this is when more P can be lost as pollution
saturation point is usually .20
How is P involved in NPS?
dissolved P in runoff
particulate P (most common) attached to soil or organic matter and moves w/sediment during erosion
leaching of P (not a large concern)
What is a primary option to mitigate P pollution?
limited options
mulch helps - doesn’t have to be completely covered, can reduce P loss by 90%
What is eutrophication?
excessive nutrients, dense growth of plant life, lose O2 in the water column, results in dead zones
What are the ultimate sources for K?
soil parent materials, mined inputs
What are the on farm sources of K?
SOM, manure, crop residues, soil mineral fraction, inorganic fertilizer
What is the plant available form of K?
K+
What are the major processes for K?
weathering (mineralization) - slow
cation exchange - fast
What is cation exchange for K?
releases K ions in return for another cation w/high affinity
What is lime?
the stealth nutrient
can increase the availability of some nutrients
composed of calcium carbonate and magnesium carbonate
principle purpose is to control pH
can alleviate deficiency problems in many cases (nutrients compete for uptake)
What is Liebig’s Law of the Minimum?
plant growth is limited by the most constrained nutrient
What are the principles of nutrient application?
economic optimization
1) fit response curve
2) estimate cost of fertilizer relative to price of crop
3) set recommendations to avoid “uneconomic” applications MC>MR
What is field level nutrient balance?
nutrient supply = nutrient removal (crop)
nutrient supply - manure, SOM, crop residue, inorganic fertilizer
nutrient removal - grain, stover removal
What is the paradigm of nutrient management?
deficiency - law of minimum guides decisions
excess - principles of nutrient balancing guide decisions
have to dance on the line
How do you estimate removal?
1.2%N * 150 bu/acre * 56 lbs/bu = 101 lbs/acre N
N concentration in corn grain - 1.2%
yields in corn grain - 150
conversion from bushels to acres - 56
How many elements are essential for plants?
18
macro - mostly from air, water, soil solids
micro - mostly from soil solids
