Ammonia, nitrate and urea utilization by orchids.
 

I was curious as to what forms of nitrogen were best utilized by orchids. Here is an interesting article that shows that Phalaenopsis utilizes urea and ammonium better that nitrate.
http://www.crh.ulaval.ca/uploads/tx_..._ca_absorb.pdf

Wow, if this holds true for other orchid genera it really blows the conventional wisdom out of the water. Thanks for the link, David!

--Nat

Biuret contamination of urea.
 

It may be that the conventional wisdom against the use of urea in orchid fertilizer is due to the possibility of the urea being contaminated with biuret.
http://www.ncbi.nlm.nih.gov/pmc/arti...00365-0068.pdf

It is believed that all plants must have urea broken down before i the nitrogen can be utilized, and that usually happens courtesy of bacteria present in soil. The common belief/assumption is that there is not a sufficient bacteria population in orchid media to accomplish that in significant volume.

I'm not going to reread that Trepanier article, but if I recall reasonably well:

1) It was not a particularly rigorous study.
2) By tagging the nitrogen in the urea and having it show up in the plants does not necessarily mean urea can be taken up directly:
a) The urea could have decomposed prior to absorption by the plant in the first place.
b) The urea could have been absorbed in the velamen of the roots, THEN decomposed before be absorbed.