ach 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 labor or equipment investment. This system gets water to all parts of the field, thus meeting the needs of all the individual plants. Gravity flow irrigation is efficient for densely planted field crops like wheat, rice or pasture. It can waste a lot of water when used on row crops or orchards because the standing water between the widely spaced plants is open to evaporation. Furrow irrigation helps direct and contain the amount of water in a gravity flow system so that it is used more efficiently.
Pressurized sprinkler systems generally use less water than gravity flow, but much of the spray through the air and the water which falls on plant leaves evaporates on hot, dry days. Placement of water is not exact because of wind scatter. This type of irrigation requires significantly more labor and equipment than gravity flow methods, but it is the only practical way to irrigate uneven ground.
Micro-irrigation uses the least amount of water but is very costly in terms of labor, equipment and maintenance. This type of irrigation eliminates drainage erosion problems. However, it cannot adequately apply water to field crops or pasture at a reasonable cost.
- Pour a gallon of water into a container. Have a student fill an eyedropper full of water from the container and water one flower or vegetable with it. Use as many eyedropper applications as necessary.
- Have the student attempt to water the flat filled with grass by the same procedure.
- Put a little silt or clay in the eyedropper. Does it clog up?
- Show different components of micro-irrigation system to the class. The AgriWater graphics on the WaterShare site illustrate both micro-spray and dripline types, and there are varieties of each. What they all have in common is the delivery of small drops close to the plant roots, at a rate matching the uptake of water by the plant. Many micro-irrigation systems require water filtration, to prevent clogging of the small water openings, or "emitters."
- Lead the class in a discussion on the advantages and disadvantages of