Nitrogen cycling

Question 1

what are some facts about nitrogen management

Answer 1

its often the most limiting nutrient for crop production, N fertilizer is one of the highest input costs to farmers, more money and effort has been spent on managing N than any other element, and N is hard to manage because the N cycle is very complex

Question 2

what are N inputs

Answer 2

N fixation

Question 3

what is internal N transformation

Answer 3

mineralization, immobilization, Nitrafacation

Question 4

what are N losses

Answer 4

denitrification, volatilization, leaching

Question 5

what is nitrogen fixation

Answer 5

the chemical reaction that converts dinitrogen gas to ammonia. it requires a lot of energy to break the triple bonds that hold the nitrogens atoms together

Question 6

what are the three different N fixations and how abundant are they

Answer 6

lightning (3% total N fixed)
biological (67% of total N fixed)
industrial (30% of total N fixed)

Question 7

what is Biological N fixation

Answer 7

turns nitrogen gas into ammonia

Question 8

what is the chemical equation to biological N fixation

Answer 8

N2 + 8H^+ +6e- —> 2NH3 + H2

Question 9

what is industrial N fixation-fertilizer

Answer 9

N fertilizers are industrial manufactures using the harbor-bosch process. N2+3H2—>2NH3

reactions require high pressures and temperature

natural gas us the source of H2

Question 10

what is the nitrogen in the environment

Answer 10

the atmosphere is comprised of 78% N2 but only a few microorganisms can use that N

very little soil N comes from rocks or minerals

over millennia the plants and microorganisms that can fix N2 contribute organic matter that contains organic forms of N to the soil when they die

Question 11

in sask how many percent of inorganic N is in the soil

Answer 11

1%

Question 12

what kind of nitrogen does the vast majority of plants take up

Answer 12

inorganic N

Question 13

if 99% of soil nitrogen is in organic matter how do plants access this N

Answer 13

1) soil microorganisms decompose organic matter releasing simpler chemical forms of organic n into the soil
2) soil microorganisms transform the simple forms of organic nitrogen (R—NH2) into an inorganic form (NH4+) through the process of mineralization

Question 14

what is the chemical equation for mineralization

Answer 14

R—-NH2 + 2H2O —> OH- + R—OH + NH4+

Question 15

what is immobilization

Answer 15

it is the opposite of mineralization: microorganisms convert inorganic nutrients into organic forms within their cellular components

the nutrients are immobilized from soil solution

plants are in competition with microorganisms for the NH4+ and NO3- in soil solution

Question 16

describe nitrogen mineralization and immobilization together

Answer 16

the process of N mineralization and immobilization occur simultaneously

Whether the net effect is an increase or decrease in NH4+ in the soil solution depends on the carbon-nitrogen ratio of the organic material being decomposed

Question 17

what ratio do microorganisms need to meet their C and N requirements

Answer 17

they need a diet of C:N=8:1

Question 18

when does mineralization occur

Answer 18

when the C:N ratio is less than 24:1

Question 19

when does immobilization occur

Answer 19

when the C:N ratio is more than 24:1

Question 20

how much carbon is eaten by microorganisms is lost as CO2 during respiration

Answer 20

16 parts

Question 21

what ratio C:N do microbes need

Answer 21

24:1. 16 parts are lost during respiration and 8 is used for maintenance

Question 22

what is the wheat straw C:N ratio

Answer 22

80:1 immobilization occurs

Question 23

what is the young alfalfa hay C:N ratio

Answer 23

13:1 mineralization occurs

Question 24

what is nitrification

Answer 24

ammonia is oxidized by bacteria in a two-step process to produce nitrate NH4+ + O2 —> NO2- + O2 —> NO3-

Question 25

what kind of soils does nitrification happen in

Answer 25

in well-aerated soils (oxygen present)

Question 26

in the soil what is present in a higher concentration: NO3- or NH4+

Answer 26

nitrification happens very rapidly there for NO3- is present in the soil in higher concentrations the NH4+

Question 27

what is denitrification

Answer 27

multi-step process performed by bacteria that converts NO3- to N2 gas under anaerobic conditions (without oxygen) NO3- –> NO2- –> NO –> N2O –> N2

Question 28

what kind of soils does denitrification happen in

Answer 28

occurs in very wet soil conditions and increases with N fertilizer application

Question 29

what is N2O

Answer 29

a very potent greenhouse gas

Question 30

in denitrification what happens to N2 if necessary steps complete the N cycle

Answer 30

N2 returns back to the atmosphere

Question 31

what is volatillzation

Answer 31

ammonium in the soil turns into ammonia in the air

NH4+(aq) + OH- —> H2O + NH3(g)

Question 32

s is ammonia volatilization likely to be higher in acidic or alkaline soils

Answer 32

alkaline soils

Question 33

how does N leaching occur

Answer 33

Nitrate is susceptible to leaching down the soil profile

Question 34

why is NO3- (nitrate) more moble and susceptible to leaching than NH4+ (ammonium)

Answer 34

because clay is negatively charged and so is NO3- so there’s no attraction unlike NH4

Question 35

What is the second most important biochemical process in the world

Answer 35

Biological N fixation

turns nitrogen gas into ammonia

in the plant, it turns NH3+organic acids–>amino acids–>protins