MadSci Network: Agricultural Sciences

Re: What is the effect of urine on plants (grass)?

Date: Mon Feb 7 15:08:22 2000
Posted By: Steven Seefeldt, Staff, Crop protection/weed science, AgResearch
Area of science: Agricultural Sciences
ID: 949363006.Ag

Hi Ben,

There is not a quick way to answer your questions and I keep wanting to 
say "it depends".  The Administrator has also asked that I expand a bit on 
what you have asked so have patience and all, I hope, will be made clear.

First, urine is acidic, however we are not dealing with uric acid when we 
are talking about mammals such as dogs and cats.  All animals need to get 
rid of excess nitrogen.  The excess nitrogen comes from the breakdown of 
amino acids when food is digested.  Many aquatic animals convert the 
nitrogen to Ammonia (NH3)and excret it.  This type of urine is only 
possible for animals that live in water as ammonia is very toxic to animal 
systems if it is concentrated, so it does not concern us.   In land 
animals ammonia must be converted to less toxic waste products that 
require less water for excretion.  Most terrestrial vertibrates produce 
Urea (H2N-CO-H2N).  Birds and reptiles produce Uric Acid (C5N4O3H4).  
(From Biochemistry by Voet and Voet  John Wiley and Sons Inc 1990).  So 
from this point on I will be talking about urea.

For the second part, does urine ruin grass?  Well, that depends.  A little 
urea is very good for plants.  It is a fertilizer that many farmers put on 
their crops as a source of nitrogen.  As with most chemicals, toxicity is 
related to the concentration.  A little salt on the french fries is very 
good, a couple of large glasses of very salty water will kill you very 
quickly.  And so it is with animals urinating on the grass.  It is a great 
fertilizer if it isn't concentrated.  Two recent articles in the Journal 
of Ecology (1996. Volume 84 pages 799-813 and 815-826 by Schwinnig and 
Parsons) go to great lengths describing the affect cow urine has on clover 
nitrogen fixation and clover/ryegrass population dynamics.  In the 
pastures of New Zealand, cow urine adds a lot of nitrogen to the soil 
which is good for the pasture.  Dog urine is thought to be bad for plants, 
but that is only because dogs don't randomly urinate around like cows in 
New Zealand.  Instead they mark their territory and pee on the same place 
day after day.  And any other dog coming by and sniffing the spot feels 
obligated to add to the spot.  Soon the concentration increases to toxic 
levels and the plant suffers and dies.  If the spot was well watered, the 
urea could be diluted to fertilizer levels.

Urine has more that just urea in it.  It is mostly water.  Depending on 
what we are eating and drinking and your health there could be of lots of 
different compounds.  My guess is that most of these would have very 
little impact on plants.

For your last question, is cat and dog urine similar to human?  I would 
have to say that it is basically the same.  All of it would mostly be 
water with urea in it and lots of other waste products depending on what 
has been eaten and the health of the individual (diabetics will have sugar 
etc.).  As far as a plant in concerned it will all be about the same.  If 
you consider yourself and your own urine, you will notice that in the 
morning it is darker because it has many more waste products in it (stored 
up in the bladder all night long).  If you drink lots of water (or eat 
lots of watermelon), it will come out very clear because you are needing 
to get rid of all the excess water in your body.  If you eat asparagus it 
will have a strong smell.  Your urine is constantly changing as your body 
deals with the process of maintaining health.

I hope this has helped.  I feel strange answering this question as a weed 
scientist, but as I had to memorize the urea cycle in the most 
excruciating detail to pass graduate level biochemistry and as I deal with 
urea based fertilizers when planting an experiment and work with Tony 
Parsons (from the Ecology articles above) I felt somewhat qualified to 
give this question a go.


Steven Seefeldt

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