Nutrients

Question 1

What are the ultimate sources of N?

Answer 1

biological, industrial, lightning

Question 2

What are the on farm sources of N?

Answer 2

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

Question 3

What are the plant available forms of N?

Answer 3

NH4+ (ammonium)
NO3- (nitrate)

some plants favor one source over another

Question 4

What are the major processes for N?

Answer 4

mineralization

nitrification

Question 5

What is mineralization of N?

Answer 5

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

Question 6

What does the rate of N mineralization depend on?

Answer 6

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

Question 7

What is immobilization of N?

Answer 7

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

Question 8

What is ammonium fixation in clay minerals?

Answer 8

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

Question 9

What is ammonia volatilization?

Answer 9

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

Question 10

What is nitrification?

Answer 10

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

Question 11

How can inorganic N be lost?

Answer 11

volatilization, many ways

Question 12

What is immobilization enhanced by?

Answer 12

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

Question 13

What conditions increase volatilization?

Answer 13

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

Question 14

What conditions increase denitrification?

Answer 14

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

Question 15

What is N20?

Answer 15

nitrous oxide
major greenhouse gas
a lot contributed by ag
NPS

Question 16

How does fertilizer N work?

Answer 16

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)

Question 17

What is the problem with nitrate?

Answer 17

it’s very mobile, can move down and laterally

major source of NPS pollution

Question 18

How can soil N contribution be estimated?

Answer 18

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)

Question 19

What are sources of N?

Answer 19

soil N
fertilizer (Haber-Bosch)
legume fixation

Question 20

What is the Haber-Bosch process?

Answer 20

get H to synthesize ammonia from atmospheric N

energy intensive process
major improvements in efficiency

Question 21

What are the consequences of Haber-Bosch?

Answer 21

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

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

Question 22

What are the ultimate sources of P?

Answer 22

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

Question 23

What are the on farm sources of P?

Answer 23

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

Question 24

What is the plant available form of P?

Answer 24

generally H2PO4-

Question 25

What are the major processes for P?

Answer 25

mineralization | immobilization

Question 26

What are problems with P?

Answer 26

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

Question 27

What is the problem with surface application of manure?

Answer 27

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

Question 28

How does P change forms?

Answer 28

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

Question 29

What is soil P saturation?

Answer 29

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

Question 30

How is P involved in NPS?

Answer 30

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)

Question 31

What is a primary option to mitigate P pollution?

Answer 31

limited options | mulch helps - doesn't have to be completely covered, can reduce P loss by 90%

Question 32

What is eutrophication?

Answer 32

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

Question 33

What are the ultimate sources for K?

Answer 33

soil parent materials, mined inputs

Question 34

What are the on farm sources of K?

Answer 34

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

Question 35

What is the plant available form of K?

Answer 35

K+

Question 36

What are the major processes for K?

Answer 36

weathering (mineralization) - slow | cation exchange - fast

Question 37

What is cation exchange for K?

Answer 37

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

Question 38

What is lime?

Answer 38

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)

Question 39

What is Liebig's Law of the Minimum?

Answer 39

plant growth is limited by the most constrained nutrient

Question 40

What are the principles of nutrient application?

Answer 40

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

Question 41

What is field level nutrient balance?

Answer 41

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

Question 42

What is the paradigm of nutrient management?

Answer 42

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

Question 43

How do you estimate removal?

Answer 43

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

Question 44

How many elements are essential for plants?

Answer 44

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