One form of irrigation commonly used for pasture grasses.  Photograph: Bill Phillips

Background
In the 1940s the average farmer could produce enough food for 19 people. Today, a farmer can produce enough food to feed 129 people. Technological advances have increased the productivity of farms, particularly by improving the ability to provide water to 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 farmers produce an abundant and diverse supply of food, fibre and foliage products. Irrigation plays an especially important role in Australia where growing seasons are long but there is not enough rainfall to supply an optimum amount of water for commercial crops. 

There are three main types of irrigation - surface gravity flow, pressurised 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 irrigator include: 

>proximity of the field or pasture to a water source
>adequate water distribution system to the paddock (pumps, canals or pipes)
>amount of water required by the selected crop
>quality of the available water
>cost of the water
>topography of the land
>type of soil
>amount of annual rainfall
>the cost of irrigation supplies
>then availability of labour to set-up and maintain the irrigation system
>fertilisation methods
>methods for recycling or handling excess irrigation water.

The complexity of choosing an appropriate irrigation system and using the available water to maximum efficiency has helped to ensure that good farmers are true water managers, very aware of conservation principles. It’s in their own best (economic) interest to use water wisely.

The method of irrigation can determine whether a crop can produce enough food or fibre to be economically viable. Water must be applied both at the right time and in the right volumes to be useful. This activity will provide students with an understanding of efficient water utilisation.

Vocabulary
Irrigation
Crop
Micro-irrigation
Drip irrigation
Ditch irrigation
Boom spray irrigation

Lesson plan
1. Divide the students into four groups, A through D. Give each group a description of their irrigation approaches and constraints (see below).

2. Then, give each student three cups filled with soil.

3. Each student is then given two bean seeds, two wheat grains, and two rice grains.

4. Have the students make a 1-2 cm deep hole in the soil in each cup and plant the seeds, each type to a single cup.

5. Have the students write their names and group number on their individual cups.

6. Assign each group a place for their cups indoors, where the plants can get plenty of light.

7. Provide each student with a Water Allocation Record Sheet (see below) to be filled in each time they ‘irrigate’.

8. Follow up 4-6 weeks: Students are likely will see a difference in growth and health of the plants as a result of these variations. 
In a follow-up discussion students can compare the growing conditions for each group.

Each group is also to consider what would cause the people to settle the land this way – what factors would change how they would settle and use the land.
Have students compare their conclusions with a geo-political map of the area. Where have people settled? How is local settlement related to their waterways and irrigation?

Secondary approach
Have students expand on their experiment in terms of crop choices or, area of land under cultivation.

IRRIGATOR GROUP TYPES

Group A: Dryland farming
You represent farmers who do not use any irrigation system. The only time you can water your plants is when it rains outside. If it is pouring rain, you should flood your cups. If it rains lightly, only a few drops are allowed. If it doesn’t rain; that’s just tough luck.

Group B: Micro-irrigation
Use a titration dropper to administer a few drops of water to your crops at frequent intervals throughout every school day.

Group C: Gravity flow Irrigation
Pour water directly into your cups until the water level reaches the rim. Only water again when the soil is dry.

Group D: Sprinkler Irrigation
Use a watering can with a flow diffuser to water your plants two times per week, applying just enough to wet the soil without flooding it.