Andre:
 
I don't know any vendors of equipment, but I do know that Lowry Harper,
USDA-ARS, Watkinsville, GA, works on NH4 compensation point of crop
canopies.  It appears that crop canopies can efflux ammonia from their
leaves when internal ammonium is high and temperature is high.  On the
other hand, canopies can also absorb ammonia from the atmosphere if their
internal ammonium status is low.  This compensation point works much like
the CO2 compensation point.  This is as a gas.  I suppose that P and K are
particulate, so find out about dust traps and filters.
 
Ken Boote
 
 
At 01:41 PM 7/13/98 +0200, you wrote:
>I plan to conduct a field experiment with maize and I am interested to
>quantify the amount of N, P and K and perhaps other elements such as
>heavy metals or acidifying agents during no rain periods (dry periods)
>as well as periods of rain (wet periods).  I am therefore looking for
>a procedure or a method to measure the deposits of these elements from
>the atmosphere.  Can you please help me in this regard by giving me
>any information you have about methods or instruments that can be used
>for this purpose, or even if you know of any similar studies that have
>been carried out.  I would also like to know the addresses of possible
>suppliers of such instruments
>
>Regards
>Andre
>