urea and nitrogen - Orchid Board

early · #1 02-15-2020, 01:55 PM

I have heard from farming, that urine, which is high in urea kills terrestrial plants. Is the salts or the urea?

Here on OB, I have read it is best not to use fertilizer that has urea .

I have both a 30-10-10 and a 20-20-20 that has as part of the nitrogen, urea.

I need help figuring out if I need to buy a 20-20-20, which I am now using weakly in S/H, that has no urea the in fertilizer.

Ray · #2 02-15-2020, 03:05 PM

It's too much urea that kills plants. A dog can pee in your yard without affecting the lawn, but if the same spot is used repeatedly, it's a different matter.

Orchids can use all three forms of nitrogen - nitrate, ammonium, and urea. The first two are preferentially absorbed by the roots, but some can be absorbed through the leaves. Urea is the converse - better foliar absorption, but can be absorbed through the roots, to a lesser degree.

With orchids, foliar feeding is generally less effective, as the waxy layers on the leaves meant to retard water loss also reduce the chance of absorption.

Both of your existing fertilizers are fine. When mixing, just remember to ratio the nitrogen - your 20-20-20 usage should be 150% of the 30-10-10 usage.

Roberta · #3 02-15-2020, 03:19 PM

I think that the advice against using urea-containing fertilizers comes from notion that because urea needs bacteria to break it down into a form that the plant can use, and because orchids don't grow in soil that such bacteria are lacking. However, orchids do have such bacteria in their roots to break down organic nitrogen-containing compounds or they would not have survived in nature... In nature, they get whatever dissolves in rainwater from rotting detritus above them, which is certainly organic. (In nature they don't get ammonium nitrate) So I totally agree with Ray, what you have is fine.

early · #4 02-15-2020, 03:37 PM

Thanks Ray, that is great information. I use 1/4 tsp of the 20-20-20 and plan to stay with that for now until I retain more info...Which is one thing at a time ….hehe

Sorry Roberta I did not see you answer until after I posted the above. Have yet to read it but will and respond.

---------- Post added at 02:37 PM ---------- Previous post was at 02:23 PM ----------

I love it when you too agree, and when you don't, I weigh each equally. You both have such backlog of knowledge, at 78, it will take my anticipate age of 104 to catch up..hehe.

Orchid Whisperer · #5 02-16-2020, 01:18 PM

Orchids (and other plants) can and do absorb and utilize urea directly. Urease, an enzyme in orchid roots, converts urea into ammonium inside root tissue.

See: https://staugorchidsociety.org/PDF/O...ySueBottom.pdf

There is a 2008 research article by Martin Trepanier that discusses root absorption and utilization of urea; the study was conducted using Phalaenopsis. See attachment:

Phalaenopsis_can_absorb_urea_directly_through_thei.pdf

From an evolutionary / adaptation standpoint, this only makes sense. Orchids live in a nitrogen poor environment (commonly epiphytes growing on trees). With urea N being one of the forms of N available, direct use of urea N is to a plant's advantage.

camille1585 · #6 02-17-2020, 01:53 AM

I have nothing else to add from the scientific side of things, but if it reassures you, I used 20-20-20 for many years and always had excellent results with it. I've been using something else for the past year, but am not as happy with how my plants are growing/flowering so will likely switch back to 20-20-20.