From: dietz@dls.net   
      
   Peter Fairbrother wrote:   
      
   > In the conditions found in soil ammonia (or rather ammonium salts, ammonia   
   > itself would just evaporate) slowly reacts with oxygen in the air to form   
   > nitrates, which is what plants and so on like.   
      
   Actually, plants can absorb ammonium ions as well.  And the conversion   
   of ammonia to nitrate is done by nitrifying bacteria, not direct reaction   
   with atmospheric oxygen.   
      
   > If you put too much nitrate on soil it washes away before the plants get a   
   > change to absorb it, as nitrates are usually very soluble in water. That's   
   > why "ammoniacal nitrogen" is considered a slower-release nitrogenous   
   > fertiliser than "nitrate nitrogen".   
      
   Ammonium salts are also very soluble in water, so that's not the cause   
   of nitrate loss.  The real cause is that clay, a significant component   
   of soil, has negatively charged surfaces.  This tends to bind positive   
   ions.   
      
   Nitrate is also lost to denitrifying bacteria, which use it to oxidize   
   organic matter.   
      
   	Paul   
      
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