Nitrogen cycling Flashcards
what are some facts about nitrogen management
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
what are N inputs
N fixation
what is internal N transformation
mineralization, immobilization, Nitrafacation
what are N losses
denitrification, volatilization, leaching
what is nitrogen fixation
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
what are the three different N fixations and how abundant are they
lightning (3% total N fixed)
biological (67% of total N fixed)
industrial (30% of total N fixed)
what is Biological N fixation
turns nitrogen gas into ammonia
what is the chemical equation to biological N fixation
N2 + 8H^+ +6e- —> 2NH3 + H2
what is industrial N fixation-fertilizer
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
what is the nitrogen in the environment
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
in sask how many percent of inorganic N is in the soil
1%
what kind of nitrogen does the vast majority of plants take up
inorganic N
if 99% of soil nitrogen is in organic matter how do plants access this N
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
what is the chemical equation for mineralization
R—-NH2 + 2H2O —> OH- + R—OH + NH4+
what is immobilization
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
describe nitrogen mineralization and immobilization together
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
what ratio do microorganisms need to meet their C and N requirements
they need a diet of C:N=8:1
when does mineralization occur
when the C:N ratio is less than 24:1
when does immobilization occur
when the C:N ratio is more than 24:1
how much carbon is eaten by microorganisms is lost as CO2 during respiration
16 parts
what ratio C:N do microbes need
24:1. 16 parts are lost during respiration and 8 is used for maintenance
what is the wheat straw C:N ratio
80:1 immobilization occurs
what is the young alfalfa hay C:N ratio
13:1 mineralization occurs
what is nitrification
ammonia is oxidized by bacteria in a two-step process to produce nitrate NH4+ + O2 —> NO2- + O2 —> NO3-
what kind of soils does nitrification happen in
in well-aerated soils (oxygen present)
in the soil what is present in a higher concentration: NO3- or NH4+
nitrification happens very rapidly there for NO3- is present in the soil in higher concentrations the NH4+
what is denitrification
multi-step process performed by bacteria that converts NO3- to N2 gas under anaerobic conditions (without oxygen) NO3- –> NO2- –> NO –> N2O –> N2
what kind of soils does denitrification happen in
occurs in very wet soil conditions and increases with N fertilizer application
what is N2O
a very potent greenhouse gas
in denitrification what happens to N2 if necessary steps complete the N cycle
N2 returns back to the atmosphere
what is volatillzation
ammonium in the soil turns into ammonia in the air
NH4+(aq) + OH- —> H2O + NH3(g)
s is ammonia volatilization likely to be higher in acidic or alkaline soils
alkaline soils
how does N leaching occur
Nitrate is susceptible to leaching down the soil profile
why is NO3- (nitrate) more moble and susceptible to leaching than NH4+ (ammonium)
because clay is negatively charged and so is NO3- so there’s no attraction unlike NH4
What is the second most important biochemical process in the world
Biological N fixation
turns nitrogen gas into ammonia
in the plant, it turns NH3+organic acids–>amino acids–>protins
