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ASP 201 > Nutrients > Flashcards

Nutrients Flashcards

1
Q

What are the ultimate sources of N?

A

biological, industrial, lightning

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2
Q

What are the on farm sources of N?

A

biological fixation by crop, SOM, crop residue, manure, inorganic fertilizer

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3
Q

What are the plant available forms of N?

A

NH4+ (ammonium)
NO3- (nitrate)

some plants favor one source over another

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4
Q

What are the major processes for N?

A

mineralization

nitrification

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5
Q

What is mineralization of N?

A 
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
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6
Q

What does the rate of N mineralization depend on?

A

temperature, moisture, aeration
limited by low temperatures
enhanced by substrate for the bacteria

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7
Q

What is immobilization of N?

A

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

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8
Q

What is ammonium fixation in clay minerals?

A

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

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9
Q

What is ammonia volatilization?

A

ammonia gas lost from soil
more pronounced as pH increases
incorporating amendments can help reduce loss to volatilization

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10
Q

What is nitrification?

A

bacterial oxidation of ammonium (biological)
necessary to make N available for plant uptake
2 step reaction - nitrosomonas, nitrobacteria
significantly increases soil acidity

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11
Q

How can inorganic N be lost?

A

volatilization, many ways

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12
Q

What is immobilization enhanced by?

A

incorporating high C residues
manure w/lots of bedding
adding materials with C:N ratios >30

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13
Q

What conditions increase volatilization?

A

warm temperatures, steady winds, high pH soils, using an N source that is volatile, not incorporation manure/fertilizer

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14
Q

What conditions increase denitrification?

A

warm temperatures, time, lots of microbial activity, saturated or near saturated conditions

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15
Q

What is N20?

A

nitrous oxide
major greenhouse gas
a lot contributed by ag
NPS

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16
Q

How does fertilizer N work?

A

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)

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17
Q

What is the problem with nitrate?

A

it’s very mobile, can move down and laterally

major source of NPS pollution

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18
Q

How can soil N contribution be estimated?

A

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)

19
Q

What are sources of N?

A

soil N
fertilizer (Haber-Bosch)
legume fixation

20
Q

What is the Haber-Bosch process?

A

get H to synthesize ammonia from atmospheric N

energy intensive process
major improvements in efficiency

21
Q

What are the consequences of Haber-Bosch?

A

water and air pollution
loss of biodiversity
increased greenhouse gases
increases soil acidification

lots of N lost - cascades to N-limited ecosystems
eutrophication

22
Q

What are the ultimate sources of P?

A

soil parent materials, mined inputs, excretion, guano, phosphate rock

23
Q

What are the on farm sources of P?

A

SOM, soil mineral fraction, crop residue, manure, inorganic fertilizer

24
Q

What is the plant available form of P?

A

generally H2PO4-

25
Q

What are the major processes for P?

A

mineralization

immobilization

26
Q

What are problems with P?

A

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

27
Q

What is the problem with surface application of manure?

A

high potential for movement in run-off, move to surface water

28
Q

How does P change forms?

A

total soil P –> solution P –> land
solution P is very small pool relative to total
plant can only use solution pool

29
Q

What is soil P saturation?

A

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

30
Q

How is P involved in NPS?

A

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)

31
Q

What is a primary option to mitigate P pollution?

A

limited options

mulch helps - doesn’t have to be completely covered, can reduce P loss by 90%

32
Q

What is eutrophication?

A

excessive nutrients, dense growth of plant life, lose O2 in the water column, results in dead zones

33
Q

What are the ultimate sources for K?

A

soil parent materials, mined inputs

34
Q

What are the on farm sources of K?

A

SOM, manure, crop residues, soil mineral fraction, inorganic fertilizer

35
Q

What is the plant available form of K?

A

K+

36
Q

What are the major processes for K?

A

weathering (mineralization) - slow

cation exchange - fast

37
Q

What is cation exchange for K?

A

releases K ions in return for another cation w/high affinity

38
Q

What is lime?

A

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)

39
Q

What is Liebig’s Law of the Minimum?

A

plant growth is limited by the most constrained nutrient

40
Q

What are the principles of nutrient application?

A

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

41
Q

What is field level nutrient balance?

A

nutrient supply = nutrient removal (crop)

nutrient supply - manure, SOM, crop residue, inorganic fertilizer
nutrient removal - grain, stover removal

42
Q

What is the paradigm of nutrient management?

A

deficiency - law of minimum guides decisions
excess - principles of nutrient balancing guide decisions
have to dance on the line

43
Q

How do you estimate removal?

A

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

44
Q

How many elements are essential for plants?

A

18
macro - mostly from air, water, soil solids
micro - mostly from soil solids

ASP 201 (5 decks)

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