esson)
- 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 each of the three fields and is suspended in the drainage water. Pour the drainage water through a coffee filter or lab filter in order to isolate the lost soil. Compare the amounts to the measured soil in the flats. How does the percentage of loss vary?
Simulate sprinkler irrigation
- Reduce the slope to a 3 degree angle. That's a 5.24% grade, or a one and a quarter inch rise for a 24" long flat.
- Using the hand trowel, create furrows in the flat (field).
- Slowly pour a gallon of water across the head of the furrows. Record drainage time and quantity for each of the three soil types.
- Have the students carve a single furrow perpendicular to the existing furrows to demonstrate how a farmer can cross rip the field during the winter to reduce water speed and erosion. Repeat the irrigation to observe the difference.
- Have the students plant one or two flowers or vegetable seedlings in each flat.
- Using the grass-planted flat or the flower or vegetable flats, pour or spray water from diffuser head of the hose or sprinkler can. Although this only approximates a pressurized system, students can observe the differences in water application and runoff between surface gravity flow and sprinkler irrigation.
- Again, have the students time the interval between application and the first dribble of runoff, and measure the quantity of runoff.
- Show samples of different types of sprinkler heads. Compare them to the ones on the school's playground.
Different soils affect the amount of water required to irrigate a field and the time it takes to complete the irrigation. Other factors, such as crop selection and land topography affect the irrigation as well. Farmers must carefully choose which type of irrigation system-gravity flow, pressurized sprinkler or micro-irrigation-is best for a particular field. The best choice will maximize the useable water available to the plant and minimize labor and equipment costs, evaporation, runoff and soil erosion.
Gravity flow irrigation uses the most water but requires the least amount of