Comparing Different Types of Irrigation Systems

This project follows the Scientific Method. Review the steps before you begin.

Creating and Testing the Drip Irrigation System

To create your own drip irrigation system, you will need to create a wicking system that allows the water to drip slowly onto the plant. We recommend doing this experiment indoors to reduce the amount of evaporation. 

1. Fill the bottle with water and keep the cap off.
2. Cut a piece of cotton string slightly longer than the straw, with at least 2 cm extra string on each side of the straw. 
3. Cut a piece of wire to the same length as the cotton string. 
4. Tie the cotton string to the metal wire at one end.
5. Feed the cotton string through the straw using the metal wire. 
6. Hold the string on both ends of the straw and carefully pull the metal wire out.
7. Detach the wire from the cotton string, leaving the string in the straw.
8. Place the straw, with the cotton string inside, carefully into the bottle with water.
9. Suction up the water through the straw with your mouth. Double-check that the cotton string is still in place on each end of the straw. The water should start to drip from the end of the cotton string.
   1. Note: If the water does not drip continuously, carefully remove the straw from the bottle, and reinsert it into the bottle to equilibrate the pressure. 
10. Connect the straw to the neck of the bottle with a piece of wire so it is held in place, as shown in Figure 4. 
11. Check that the end of the cotton string outside of the bottle arches over and dips under the water level inside the bottle. Generally, the lower the cotton string is below the water level, the more water should drip. 
12. Ensure the water is dripping, and adjust the wiring and placement of the straw with the cotton string inside, as needed. 
13. Test your irrigation system by putting an empty measuring cup under the external end of the cotton string of the drip irrigation system. Measure the amount of water dispensed by the irrigation system over a few days. We recommend 1 week or 7 days.
14. Record the amount of water dispensed by the irrigation system and the number of days watched in Table 1. This will be the volume you use for the other irrigation systems. 
15. Calculate the amount of water distributed by the drip irrigation system and divide by the total number of days observed using the following formula. Record this calculation in Table 1. 

Image Credit: Laura Ohl, PhD / Science Buddies

Image of homemade bottle drip irrigation system created from materials of project.

Equation 1: 

Comparing Irrigation Systems Impact on Soil Moisture and Plant Growth (Weekly)

To compare the irrigation systems, you will need to set up three pots to test each type of system. Ensure the pots have drainage holes to prevent water retention around the roots, which could affect your results. Repeat the experiment three times for reliable results, making new data tables for each trial. Alternatively, you could test and run all three trials simultaneously, requiring nine pots, 3 drip-irrigation systems, and 3 olla pots. Watch the plants for the recommended time to grow on the seed packet, and collect the plant roots on the anticipated harvest date. The instructions below are written for one trial of each irrigation system.

1. Fill 3 pots half way full with soil.
2. Pre-wet your clay pot or olla with water before putting it into the soil. 
3. To 1 pot, add your olla or clay pot in the middle of the planting surface. Add the rest of the soil around but not in the olla or clay pot. The water will seep through the clay pot to help reach the plants' roots.
4. Fill the other 2 pots to the same height with soil. 
5. Plant 3-4 of the same seeds per pot. Space them evenly throughout the pot, to ensure they have the same accessibility to nutrients and water. Place each seed around the pot as seen in Figure 5 below, to keep each experiment consistent. 
6. Follow the instructions on your seeds to bury them at the correct depth in the soil.
7. Create a data table, like Table 2, for each trial of each week of the experiment. 
8. Add the same amount of water into each system in the center of the pot, watering once per week (except for the drip irrigation system, which is continuous). Record the water volume used each week, for each pot, in Table 2. 
   1. Drip Irrigation - Use your calculations from Table 1 to approximate the amount of water that will be dispensed into the pot using the drip irrigation system. Check daily to make sure that the water is still dripping daily. If not, adjust the string to the same height as before or refill the bottle so the water level is above the external cotton string until it drips again. Only adjust your set, if needed, to ensure the plants get water. 
   2. Surface Irrigation - Determine the weekly amount of water measured from Table 1 from the drip irrigation system. Measure the same amount of water and pour it into the center of the soil in the pot once weekly.
   3.  Olla Irrigation - Determine the same amount of water used for the drip irrigation system (as you did for the surface irrigation condition) and pour the exact same volume of water into the olla once each week. Cover the top of the olla to reduce or prevent evaporation (optional).   
      1. Note: Use your weekly water volume results from Table 1 of the drip irrigation system to determine how much water you should add weekly to the surface and olla irrigation pots. For the most reliable results, the water volume should be consistent between each type of irrigation system and each trial. Note in your data table if you make a mistake since this could impact your results.
9. Record the following in your lab notebook each week of the experiment, using Table 2 below as an example.
   1. Record the water volume used each week while watering each pot. 
      1. Note: This should be the same for each experiment, but if errors are made, note them. 
   2. Record the frequency of watering each plant for each week. 
      1. Note: This should be the same for each experiment, but if errors are made, note them.
   3. Measure the soil's moisture every other day, up to three times a week.
      1. To measure the soil moisture, insert the hygrometer into the soil at the same depth for each measurement. 
      2. Wait 30-60 seconds before reading the moisture on a scale of 1-10, and record your results in Table 2. 
   4. Calculate the average weekly moisture of the soil using Equation 2 below. 
   5. Measure the height of each plant weekly. Measure from the base of the plant where the green touches the soil, to the highest point of the plant. Be consistent with your measurements throughout the experiment.  
   6. Calculate the average plant height using Equation 3. 
      1. Note: If a seed did not germinate, exclude it from this calculation.
   7. Create a new data table, like Table 2, for each week of the experiment. 

Image Credit: Laura Ohl, PhD / Science Buddies

Seeds placed similar distance around center compared to olla placement, to ensure water at center reached seeds similarly for all conditions.

Equation 2. 

Equation 3. 

Comparing Irrigation System's Impact on Germination and Root Length

1. Record the following in your lab notebook to note when germination occurs and observe how irrigation impacts root development, using Table 3 below as an example.
   1. Observe the seeds daily throughout the experiment to look for germination.
   2. Record the time it takes for each seed to germinate (see plant emerge above ground), in Table 3. 
   3. Calculate the average germination time for each trial of each pot in days (see Equation 4). 
   4. At the end of the experiment, measure the longest root of each of the plants for each condition. 
      1. If the soil is dry, pre-wet it with some extra water. 
      2. Mark the base of the plant, where the shoot (or green part of the plant) meets the roots at the soil's surface. 
      3. Ensure that you keep track of which plants belong to each condition! 
      4. Gently pull out each plant to expose its roots. 
      5. Measure the length of the roots from the mark or cut of the plant to measure the longest root's length, and record your measurements in Table 3. 
   5. Calculate the average root length for each condition (see Equation 5).

Equation 4.

Equation 5.

Conclusion

• What are the advantages and disadvantages of watering frequency and water volume required for each type of irrigation system? 
• How did the moisture level change throughout the week for each irrigation system? How did active irrigation compare to the two passive irrigation methods? Was passive irrigation better at keeping soil moisture level consistent?
• Did one type of irrigation accelerate germination time, or did they all perform similarly?
• What is the relationship between soil moisture and root length? Do irrigation types with more consistent or less consistent weekly moisture yield longer roots? 
• Does plant height correlate with soil moisture? 
• How close is each irrigation system's water to the plant's roots? Does this have an impact on root development? Use your data to inform your answer.