 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 this type of system.
- Define irrigation.
- List two advantages and disadvantages for each type of irrigation system.
- Which irrigation system might be the most appropriate in the following situations:
- Large 50 acre pasture with grass and a nearby creek
- An almond orchard
- A wheat field
- A tomato field
- Forage grass on uneven ground
- Why is it important that the farmer not use too much water?
- Define erosion.
- After reviewing on the AgriWater home page the irrigation graphic showing the farm, sketch how water is moved from a river to a field.