NITROGEN Vitousek May 3 2010
<p>May 12, 2010 12:45 PM
 
Peter Vitousek  is Stanford faculty.
 
talks abt  anthrpogenic effects on nitrog balance.
 
Dinitrogen  = N2  is  78% of the atmos.
 
it is freq. the element in shrotest supply for many organisms.
 
Nitrog  cycle has been altered at a greater extent than the C-cycle by man.
 
Natural  bio fixation of N2  =  70 to 100 Megatons
 
Lightning is  5  Mtons
SO  total Natl fix.  =  75 to 105  Mtons.
 
MANKIND
 
Manufact of  Nitrogen fertilizer  (Haber-Bosch) Process    =  100  M tons
CROP  N2  fixation  (by soybeans, peans  using orgs in their roots)  =  30 Mtons.
Fossil Fuels  =  25  M tons
    Industrrial Use  = 20
 
TOTAL of  Human Use  =  175  M tons.
 
Only way that  nitrate  gets back as N2 into atmos  is by
DENITRIFICATION  (eg  when nitrate goes into a BOG.
 
Effect on  Nitrog  exactly tracks  human effects;
 
First came deforestation in the 1700s and earlies  then
CO2 rise  in 1800's
then  Human ???
then industrial  (Haber process)   massive recent effect.
 
MOST of this effect has been since  1995 !!!!
 
Get greatly enhanced crop yields by adding N fertiliz.
 
Similar dynamics for inorg phosphate.
 
this is huge  vs  rock breakdown.
 
Most of  nitr  on crop  runs off...  50%  effic is typical.
 
Nitr  cuz  algaw  overgrowth.  =>  pond scum in estuaries...  kills them.
 
causes  hypoxic zone  in the oceans also.
Green scum   algae uses all the O2 in the water.
 
Nitrous Oxide is  N2O  N=N-O
 
big  increases in  NOx  and NH3 and Methane in the atmosphere  since 1800.
 
in primordial times  methance was  at  750  (baseline)
it is now at  1750   !!!!
 
incr  N2  leads to incr agric prod  but  decreased  diversity.
 
there is incr  in reactive Nitr  over  intensive  agric areas of the plant  eg in the N hemisphere.
 
in cr N  leads to an incr in reb brome grass  ,  a non-native that
is now in the  Mojave  all the way to LA.
 
They need more N  ferti  i  Kenya... not enuf fertiil.  need more N and P.
 
In China,, oppositve  ... hug xs  of Nitr on the crops  aand it washes away.
USA is just right in terms of crop fertiliz.
 
CHINA has 1.3 B people.
 
China now has enuf grain for its population.
but alot is going into the groundwater  (the fertiilzier)
 
India ... similar to China.
 
Why  the process of converting Natl Gas to Fertilizer is heavily subsidized...
slow to turn this off.
 
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