Bureau of Reclamation Mid-Pacific Region Banner
Reclamation Home             Reclamation Offices             Newsroom             Library            Projects & Facilities
A white, oval shape logo, with the title WaterShare centered in green letters.  There is a blue drop of water and the title.

Elementary School Lesson Plan

by Rich Engel, M.A.

Water Those Plants

This lesson will introduce students to the three basic types of irrigation: surface gravity flow, pressurized sprinkler and micro-irrigation.

Students will:
  • Recognize the three main types of irrigation systems
  • Distinguish the appropriate conditions for each system
  • Identify the many factors affecting irrigation

Key Ideas:

  • Plants need water
  • there are many ways to water plants
  • too much water is not good for the plant
  • too little water is not good for the plant
  • irrigation can supply just the amount of water a plant needs
Subjects:

Science - Comparing similarities and differences, describing, demonstrating, observing, listening, recording, discussing

Performing Arts: - Creating, building

Background Information:

In 1940 the average farmer in the United States could produce enough food for 19 people. Today, an American farmer can produce enough food to feed 129 people -- 101 in the United States and 28 abroad. Technological advances have increased the productivity of farmers, particularly by improving their ability to provide water to their crops through irrigation. Irrigation is defined as the managed application of water to soil for the purpose of increasing crop production.

Irrigated agriculture has helped American farmers produce the most abundant and diverse supply of food, fiber and foliage products in the world. Irrigation plays an especially important role in the Western United States where growing seasons are longer but there is not enough rainfall to supply an optimum amount of water to commercial crops. California alone produces over 250 agricultural commodities, most of which could not be grown there without irrigation.

The following AgriWater information and activities will focus on the three main types of irrigation - surface gravity flow, pressurized sprinkler, and micro-irrigation. In order to select the appropriate type of irrigation, the farmer must make informed decisions. Water availability, economics, soil types and plant biology factors must all be studied before choosing an irrigation technique. Some of the major considerations for the farmer or rancher include:
  • proximity of the field or pasture to a water source
  • adequate distribution system to the field (pumps, canals or pipes)
  • amount of water required by selected crop
  • quality of available water
  • cost of water
  • topography of the land
  • soil type
  • annual precipitation
  • cost of irrigation supplies
  • availability of labor to set-up and maintain irrigation system
  • fertilization methods
  • methods for recycling or handling excess irrigation water

The complexity of choosing an appropriate irrigation system and utilizing the available water productively has helped to insure that good farmers are true water managers, very aware of conservation principles. It is in their own best economic interest to use water wisely.

Activity 1: Delivering water where and when it is needed: Save the Tomatoes!

Activity Background:

All life forms on Earth, including children and plants, need water for health and growth. In wild nature, plants have water needs suited to where they are located. Native plants in dry regions make the best of what water they get, when they get it. But almost all cultivated crops need a lot of water, frequently applied. Farmers can grow these food crops in dry places by bringing the water to the fields, a process called irrigation. Irrigation methods differ depending upon the amount of water required and the size of the area to be watered, among other factors.

Pound for pound, acre for acre, plants require more water for healthy growth than people do. When you are thirsty you may drink a glass of water to quench that thirst. Over an entire year your body will require a few hundred gallons. But tomatoes planted on an acre of farmland (an area the size of a football field) may in the course of a few weeks consume 650 thousand gallons of water as they grow to ripeness--enough water to cover that acre two feet deep. The same amount of water could meet the complete residential needs of an average family for a few years.

Plants don't get thirsty, though, they just respond to the amount of water available. The whole point of irrigation is to supply enough water so that the plants produce plenty of leaves, stems, roots, flowers or fruit. Some crops might even survive without irrigation in a dry climate, but they would not produce much to harvest and sell. Supplying too much water does not help plants either, and can even hurt them. Excess water costs money without providing any benefit. Farmers must choose the right type of irrigation system for their crops so that the water arrives at the right time, on the right place, and in the right amounts.

Preparation:

1 Hour

Estimated Teaching Time:

1 Hour

Questions for discussion:
  • Why do plants need water?
  • How do you water plants at home, indoors and outdoors?
  • How much water do you drink in a week during warm weather?
  • How much water does your lawn get in a week during warm weather? Your house plants?
Procedure:
  1. Explain this role playing game: the students are tomato plants and the classroom is a field of tomatoes. They each are at a critical point in their growth, needing water to mature their fruit. The weather is dry and hot. If any tomato plant goes too long without water its tomatoes will shrivel.
  2. Pass out 1 Dixie cup to each student/tomato. Half a cup-full represents the water needed to save the tomatoes
  3. Start the clock. They all need water at the same time. The longer the wait, the more the tomatoes shrivel, and they are shriveling fast. Have the students pretend they are talking tomato plants, reporting their condition over time.
  4. Fill one pitcher with water and begin to fill each student's cup half full, returning to the classroom sink for more water.
  5. Have the students time how long it takes to get water to the whole class/tomato field.
  6. When every cup is half full, lead a discussion on how long it took, and how much damage was suffered by the tomatoes. Ask the student/tomatoes for ideas about how to get all the cups filled in less time. Someone is sure to suggest that the teacher/farmer needs help in pouring water.
  7. Turn one of the tomato students into an irrigation helper, and go through another round of filling the cups, this time with two pitchers and two pourers, keeping track of the time. The tomatoes need water just as before.
  8. How long did the irrigation take this time?
  9. Ask the class:
    • Did the tomatoes do better with less waiting in the hot, dry summer sun before they got their water?
    • Ask a silly question: What if only one student was a tomato plant and the rest were irrigator helpers? Would that be a waste of effort and water? If the farmer had to pay all those helpers with ripe tomatoes, could that one tomato plant produce enough to meet the payroll?
Follow Up:

With two people pouring water, the task was completed much faster. However, it took double the human resources to get the water to the student/tomatoes. Farming is very similar to this activity. A farmer might use very little effort getting water to the crops. However, the plants would not all get the water at the same time. The plants that waited long would suffer reduced productivity. The more resources and energy the farmer puts into irrigation, though, the faster and more efficiently the crops are watered. This benefit must be weighed against the higher cost of a bigger irrigation effort.

Conclusion: Delivering water to crops at just the rate they need it, is a very challenging task. The job of irrigation can be a continuous effort during the growing season. It may take five days to get a field entirely watered. And then it has to be done again!

 

Activity 2: A Comparison of Irrigation Systems: Amount and Method

Activity Background:

The method of irrigation can determine whether a crop can produce enough food or fiber to be economically feasible. Water must be applied both at the right time and in the right amounts to be useful. This activity will provide students with an understanding of proper water utilization.

Preparation:

1-2 Hours

Estimated Teaching Time:
  • One 1-hour session initially
  • Several small reminders throughout the month
  • A 1 to 2 hour follow-up session
Materials:
  • Styrofoam or paper cups (1 per student) filled to within an inch of the top with soil
  • Markers
  • Six eyedroppers
  • Extra cups
  • Bean seeds (2 per student)
  • Watering can
  • Clock, watch, or stopwatch
Procedure:
  1. Divide the students into five groups, A through E.
  2. Give each student a cup filled with soil and two bean seeds.
  3. Have the students make a hole 3/4" deep in the soil and plant the seeds.
  4. Have the students write their names and group number on their individual cups.
  5. Assign each group a place for their cups indoors, where the plants can get plenty of light.

Group A: Dryland Farming

The first group represents farmers who do not use any irrigation system. The only time these students can water their plants is when it rains outside. If it is pouring rain, they have to flood their cups. If it rains lightly, only a few drops are allowed. If it doesn't rain, tough.

Group B: Micro-irrigation

This group will use eyedroppers to administer a few drops of water to their crops at frequent intervals throughout every school day.

Group C: Gravity flow Irrigation

Members of this group will each take one cup of water and pour it directly into the planted cup until the water level reaches the rim. The students will observe the plants and only water when the soil is dry.

Group D: Sprinkler Irrigation
These students will use a watering can with a flow diffuser to water their plants 2 times per week, applying just enough to wet the soil without flooding it.
Follow up:

Preferably, the primary difference between these groups will be the amount, method and frequency of water application. Students likely will see a difference in growth and health of the plants as a result of these variations. The micro irrigation students who undertake their assignment conscientiously should see the best results. As this is simply a familiarization exercise, not a controlled experiment, other variables will affect successful germination and growth. In a follow up discussion students can compare the growing conditions for each group. (And some people have a green thumb, some don't.)

Conclusions: There are many ways to water crops. Farmers select a method that applies water efficiently with productive results. When all other factors are held equal, small steady doses of water provide the best results, while requiring the most attention.

top