|MadSci Network: Agricultural Sciences|
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. Cheers, Steven Seefeldt
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