Growing Great Gardens: Using Human Urine as a Fertilizer
AbstractEvery day farmers around the world apply commercial fertilizer to their fruits and vegetables to improve plant health and yield. But applying commercial fertilizer is expensive and not economically possible for some farmers in developing countries. What if they could find a way to fertilize plants cheaply? It turns out that human urine is rich in the nutrients that plants need to grow. Could urine serve as a fertilizer substitute? Find out for yourself in this plant growth science project.
ObjectiveDetermine if diluted human urine is an effective fertilizer for plants.
Michelle Maranowski, PhD, Science Buddies
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Last edit date: 2018-12-03
Plants need nitrogen, phosphorus, and potassium in order to grow and be healthy. Many home gardeners and farmers apply fertilizer to their gardens to supply their plants with the necessary nutrients. However, in some parts of the world, the soil is depleted of all nutrients, and farmers are too poor to purchase a pre-made fertilizer. As a result, people in these areas face the risk of going hungry and becoming poverty-stricken.
What can farmers who wish to fertilize their fields inexpensively or who wish to use a natural and green fertilizer do? The answer may be to use human waste as fertilizer. Green fertilizer is made without harming our environment and is naturally replenished. We humans are continually creating waste that can be put to good use. Watch the video on the right to learn more about how the non-profit organization SOIL uses dry toilets to create fertilizer and replenish the soil in Haiti.
For the purposes of this science project, you will focus on fertilizer made from human urine. Are you shocked? Don't be— even NASA has experimented with using urine as a fertilizer! First, urine is relatively clean. In fact, human urine in the bladders of individuals without bladder and kidney infections is sterile. At the beginning of urination, the flow takes with it any bacteria in the urethra, cleaning the urethra but contaminating the urine. Mid-flow urine is then sterile. Second, urine contains many plant-friendly compounds. Human urine is approximately 95% water. The remaining constituents are, in order of decreasing concentration, nitrogen-rich urea, chloride, sodium, potassium, creatinine, and other compounds.
How does the nutritive content of commercial fertilizer compare to that of urine? Well, it depends on the purpose of the fertilizer. Urine is 18% nitrogen, 2% phosphorous, and 5% potassium, which is abbreviated as 18-2-5. These three numbers give the percentage of the nitrogen, phosphorus, and potassium by weight in the fertilizer. In other examples, fertilizer for roses is 18-24-16 and for vegetables is 18-18-21. The nutritive content of urine is similar. But is it similar enough? In this plant biology science project, you will create and test fertilizer made from your own urine. You will compare the growth of tomato plants grown in soil fertilized with your urine and those that are grown in soil with no fertilizer. Do you think that it will make a difference?
Terms and Concepts
- How does the human body create urine?
- How is commercial fertilizer made?
- How do nitrogen, phosphorus, and potassium benefit plants?
- How does urine-based fertilizer affect the taste of vegetables?
- Binford, G. (n.d.). Chapter 8: Commercial Fertilizers. In G. Evanylo (Ed.), Mid-Atlantic Region Nutrient Handbook. (189-206). Retrieved February 14, 2011, from panutrientmgmt.cas.psu.edu/pdf/rp_MA_Chapter8.pdf
- Boyle, R. (2009, September 4). Better Tomatoes Via a Fertilizer of ... Human Urine? Retrieved February 15, 2011, from www.popsci.com/environment/article/2009-09/fertilizer-future-might-be-closer-we-think
- Cooper, E. (2011). How to Use Urine as a Fertilizer. Retrieved February 13, 2011, from www.howtodothings.com/home-garden/how-to-use-urine-as-a-fertilizer
- Kristof, N. (Interviewer). (2010, March 1). On the Ground with Nicholas Kristof: American Ingenuity in Haiti. Retrieved February 13, 2011, from www.oursoil.org/
- Overcash, D. (2011). Understanding Fertilizer Numbers: N-P-K. Retrieved February 13, 2011, from www.learn2grow.com/gardeningguides/fertilizer/basics/understandingfertilizernumbers.aspx
- Pradhan, S., Nerg, A., Sjoblom, A., Holopainen, J., & Heinonen-Tanski, H. (2007, September 26). Use of Human Urine Fertilizer in Cultivation of Cabbage (Brassica oleracea)— Impacts on Chemical, Microbial and Flavor Quality. Journal of Agricultural Food Chemistry, 55(21), 8657-8663. Retrieved February 13, 2011, from pubs.acs.org/doi/full/10.1021/jf0717891
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Materials and Equipment
- Dirt without added fertilizer, (5 cups). You can find plain dirt at a vacant lot or construction site. If you harvest dirt from a construction site, ask the site manager permission before you do so. Warning: commercial potting soils have fertilizer already added to them; they are not suitable for this project.
- Baking pan, disposable, 13 inches X 9 inches
- Aluminum foil (1 roll)
- Ovenproof gloves
- Digital thermometer, available from Carolina Biological, item #: 745360
- Kitchen timer
- Jar and lid (1). Use a jar that is the size of a 25.5-ounce spaghetti sauce jar. Make sure that the jar and lid are completely cleaned and dried.
- Tomato seedlings (8). Seedlings can be purchased at your local nursery.
- Pots, 6 1/2- inch diameter (8)
- Human urine. Make sure that you have no bladder, kidney or urinary tract infections prior to starting this project.
- Disposable gloves. Can be purchased at a local drug store or pharmacy, or through an online supplier like Carolina Biological Supply Company. If you are allergic to latex, use vinyl or polyethylene gloves.
- Measuring cup, 1 cup
- Wood paint stirrer (1). You can usually get these for free from a paint store or hardware store.
- Watering can
- Permanent ink pen
- Digital scale, such as the Fast Weigh MS-500-BLK Digital Pocket Scale, 500 by 0.1 G, available from Amazon.com
- Lab notebook
- Graph paper
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For health and safety reasons, science fairs regulate what kinds of biological materials can be used in science fair projects. You should check with your science fair's Scientific Review Committee before starting this experiment to make sure your science fair project complies with all local rules. Many science fairs follow Intel® International Science and Engineering Fair (ISEF) regulations. For more information, visit these Science Buddies pages: Projects Involving Potentially Hazardous Biological Agents and Scientific Review Committee. You can also visit the webpage ISEF Rules & Guidelines directly.
Preparing the Seedlings
The dirt that you have may be contaminated with bacteria or fungi. The first step is to sterilize the dirt.
- Preheat the oven to 200°F.
- Pour the dirt evenly in the pan. The dirt should be no more than 3 inches thick, and the layer should be loose and not compacted.
- Moisten the dirt thoroughly. The dirt should be wet but not soupy.
- Cover the pan with aluminum foil and put it in the preheated oven.
- With the thermometer, check the temperature of the dirt until it is 180°F in the center of the pan. Once it reaches this temperature, let the dirt cook for 30 minutes, and then, turn off the oven.
- Let the dirt cool in the oven until you are ready to use it.
- Once the dirt has cooled, split the dirt equally into the eight pots.
Remove a tomato seedling carefully from its planting pot. Gently remove the surrounding dirt from the roots. Because the roots are young and fragile, take some time doing this.
- Once the majority of the original planting soil has been removed, wash the roots under a slow stream of tap water to clean the roots completely. This step is important, because the soil in the pots contains fertilizer. You should remove all traces of that fertilizer so that you can start your project with unfertilized plants.
- Now plant the tomato seedling in one of the eight pots that you prepared in step 2.
- Repeat steps 2–4 for the remaining seven tomato seedlings.
Initial Fertilizer Treatment
Go and harvest your urine. This step is similar to collecting a urine sample at the doctor's office.
- Urinate into a toilet for a few seconds (to get rid of any contaminated urine) and then, capture the rest of the urine in the clean jar. This mid-flow urine will be sterile. See the Introduction for an explanation of why. When you are done, cover the jar with the lid.
Now make the fertilizer. Put on a pair of disposable gloves. Measure out 1/2 cup of urine and pour it in the bucket. You will dilute the urine to create the fertilizer. Urine is too strong to use on seedlings by itself. You need to dilute it so that it doesn't burn the plants.
- You will mix 10 parts water and one part urine. Since you have 1/2 cup of urine in the bucket, mix in 5 cups of water. Stir the liquids together with the paint stirrer.
- Separate the eight pots into two equal groups. Mark the first group with a "1" on the pot and the second group with a "2" on the pot. The first group will get the urine fertilizer, along with regular watering, and the second group will get just regular watering.
- Water the plants in Group 1 (all four plants) with the fertilizer. Pour some of the fertilizer into a watering can to make it easy to water the plants. Hold the pot over the bucket to collect the excess fertilizer. Water only around the perimeter of the pot and not directly on the plant or the leaves. Don't over soak the plant. Water just until a few drops of liquid start to come out of the bottom of the pot.
- Water the plants in Group 2 (all four plants) with plain water. Don't over soak the plant. Water just until a few drops of water start to come out of the bottom of the pot.
Place the plants in a sunny location outdoors, if it is warm enough, or indoors if it is too chilly outside. If the daytime temperature is greater than 68°F, you can keep your plants outdoors during the day and bring them in at night. If you keep your plants indoors, place them in a spot that gets plenty of sun. Note down in your lab notebook the date and time that you planted, fertilized, and watered the plants. Remove the disposable gloves.
- If the plants grow too big for the original pot, you may have to repot them so that they continue to grow.
- Keep your plants out of the rain so that you can control how much water they get.
Monitoring and Feeding Your Plants
Check your plants daily. If the soil is dry, water the plants with plain water. Don't fertilize the plants in Group 1 daily. Urine is salty, and fertilizing daily could add too much salt to the soil and harm the plants.
- Measure the size of the biggest leaf of each plant in Group 1 and Group 2 every third day. Measure the length and the width at the widest point. Record the date and the measurements in your lab notebook.
- Count the number of leaves on each plant every third day. Record this data in your lab notebook.
- If the leaves of the fertilized plants start to yellow or the plant looks as if it is struggling, then dilute your fertilizer more by adding extra water.
Fertilize the plants in Group 1 on a weekly schedule. Fertilize the plants in Group 1 on days 7, 14, 21, and 28 after planting.
- Always wear a pair of disposable gloves when handling your fertilizer.
- Mix a new batch of fertilizer following the instructions in step 2 of the previous section. Change the dilution if the leaves are yellowing and the plants look distressed despite regular watering. Try changing the dilution to 20 parts water (10 cups) to one part urine (0.5 cups). Record the change in dilution and when you made the change in your lab notebook.
Collecting and Analyzing Your Data
- A week after the last fertilizing (35 days after planting), gently uproot the plants from each group and carefully remove and wash the soil from the roots.
Using a digital scale, weigh the uprooted plants and record the data in your lab notebook.
- Observe the color of the roots for the plants in each group. Are they white, yellow, or brown?
- Record the number of root hairs that you see on the roots for each plant.
- Compare the growth of the plants in Group 1 and in Group 2. Calculate the area of the largest leaf for each plant in both groups on each day that you made measurements. You may have to make an estimation about the shape of the leaf. See Figure 1 to learn how to estimate the shape of the leaf in order to calculate its area. Record your data in a table in your lab notebook.
Figure 1. This image gives an idea of how to estimate the area of a leaf using an ellipse (oval) and triangle.
- Average the area data by group and day. Record the data in a table in your lab notebook.
- Average the number of leaves on the plants by group and by day. Record the data in a table in your lab notebook.
- Plot the average area data. Label the x-axis Day and the y-axis Average Area. Use different colors for Group 1 data and Group 2 data in order to differentiate between them.
- Plot the leaf area data points for both groups by day. Use one color for all the points in Group 1 and another color for all the points in Group 2. This graph will show you the range of the data.
- Plot the average number of leaves for both groups by day.
- Is there a difference in the average growth between the plants fed with the urine-based fertilizer and the plants just given water? Is there a difference in the roots between the two groups? Does the range of the data between the two groups vary? Does the average number of leaves by group vary? Overall, do you think that using urine-based fertilizer is a good choice for feeding plants?
If you like this project, you might enjoy exploring these related careers:
- Try urine-based fertilizers on different plants, such as cabbage or corn. Do you have to use fertilizer diluted in the same proportion as for the tomatoes?
- Compare urine fertilizer with store-bought fertilizer on tomato plants. Grow the plants until they start to fruit. Did one type bear fruit before the other? Compare the quantity of fruit that you get from the plants that are fertilized with urine and the plants that are fertilized with store-bought fertilizer. What is the average weight of the fruits from both types of plants? Is there a difference?
- Try a taste test between vegetables grown with the urine-based fertilizer and vegetables grown conventionally with store-bought fertilizer. Gather together a group of 20 taste testers and investigate whether they can tell the difference between the urine-fertilized plant and the plants grown with store-bought fertilizer.
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