y introduces students to the three main types of irrigation systems and the advantages and disadvantages of each.
Questions for discussion:
- Have the students take a pinch of each of the soil samples with dry fingers, feeling the particles, smelling them, then wetting them slightly, feeling and smelling the change.
- Ask them to examine the pinches of soil with the magnifying lens.
- Explain the differences between sand, silt and clay.
- Place individual soil samples into each of the clay pots.
- Place each clay pot into its own jar.
- Pour equal amounts of water (100 ml) into each of the three pots in succession (Start with the sand, then the silt, then the clay).
- Time the period from water application until the flowerpots stop leaking. (About 15 minutes)
- Measure the amount of water collected in each of the jars under the pots. Optionally, measure the before and after weight of each of the soil-filled flowerpots, to find the weight of water retained.
- Have the students complete a simple lab report on this activity. Be sure to have them include a description of the procedure, observations during the experiment and an explanation of results.
- What are the three main types of irrigation systems?
- List one advantage and disadvantage of each.
- What are the goals of irrigating?
- How does crop selection affect irrigation techniques?
Conduct the demonstration, or group activity models as follows:
- Three 24"x24" nursery flats with solid bases (or a cardboard insert to cover drainage holes)
- Three strips of rag cloth two feet long, one for the top end of each flat
- A metal or plastic gutter for collecting runoff at the bottom of each flat (can be reused)
- 3 liters water - minimum
- 1 water dropper
- 1 garden watering can or hose nozzle with spray diffuser
- 1 garden trowel;
- 1 graduated cylinder or measuring cup (should hold at least 1 liter)
- 1 "six-pack" flower or vegetable seedlings
- 1 flat of grass or ground cover material from local nursery (can be purchased or planted from seeds 3-4 weeks prior to lesson)
- 1 stop watch
- Samples of drip or micro-sprinkler components and sprinkler heads (contact local farmers, or university extension, or an irrigation equipment supplier, or a US Bureau of Reclamation Water Conservation Coordinator)
Simulate gravity flow irrigation:
- Lay each strip of rag cloth along an edge of each flat
- Measuring out the soil, fill the three nursery flats level to the top with sand, silt and clay, respectively.
- Lightly compress each soil, being careful to not overly compact it.
- Prop up the rag covered edge of each flat at approximately 5 degrees with bricks or boards on a desk or table. (Pop Quiz: to find the rise in inches, multiply the sine of 5 degrees by 24 inches. If the students have not had that level of math, calculate the rise by the grade of the slope. A 5 degree angle is the same thing as an 8.75% grade, meaning the rise equals 8.75% of the horizontal travel. Is the horizontal travel equal to or less than the length of the flat? Turns out that for such small angles, the difference can be ignored. If you don't want to bother with any of this math, prop up the 24" flat so the top is 2.1" higher than the bottom. Farmers figure this all out using laser beam surveys.)
- Position the gutter under the lower end of the flat to catch drainage water.
- Place the graduated cylinder or other catch device in a position to capture the water as it runs off of the gutter, or pour the gutter water into the graduated cylinder when drainage is complete.
Simulate furrow irrigation.
- Slowly pour a gallon of water directly from the container back and forth across the rag strip at the top of the flat containing sand. (Using the rag avoids having the soil wash away from the impact of the water.) Have the students time the intervals from water application to the first dribble of drainage. Repeat for silt and clay.
- Measure the amount of water drained from each of the types of soil.
- Record the drainage time and quantity of water drained from each soil type.
- Observe how much soil runs off of e