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:
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.
- 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
Basin irrigation, pressurized sprinkle irrigation, micro-irrigation, soil type, drainage, water holding capacity, saturation, runoff, water conservation.
Activity 1: Comparing the water holding capacity and speed of water saturation:
Different soils hold different amounts of water in the spaces between the soil particles. The amount of moisture a soil can retain per unit of soil volume is called its holding capacity. Holding capacity determines the quantity of water an irrigator must apply to a particular field and the frequency of the water application. In this lesson students will observe and demonstrate the different water holding capacities of sand, silt and clay soils.
Sand, silt and clay are distinguished physically by the size of the particles: sand having the largest and hardest particles, silt having fine, gritty particles, and clay having extremely fine, powdery particles when dry. The difference in particle size results in a difference in the available pore space between particles. The smaller the pore spaces, the more strongly water will cling inside them. Most soils are various mixtures of sand, silt, and clay, and a given field may contain different types of soil.
- 1-2 Hours
- Estimated Teaching Time:
- Three 1-hour sessions
- Opportunities for up to five 1-hour session follow-ups
Questions for discussion:
For one class demonstration or one participation activity for 3-5 students:
- What are the physical differences between sand, silt and clay particles?
- Which soil will pass water through to the jar the fastest? Why?
- Which soil type will absorb the most water? Why?
- Three transparent wide-mouth jars, each 1 to 3 liters in capacity
- Three small clay flowerpots with holes in the bottom, each 1-2 cups in capacity, of a shape and size that will fit inside the jars
- 1 cup of each of the following types of soils: sandy, silty and clay (get these from a local nursery)
- 1 water measuring device (graduated cylinder or flask).
- 1 stop watch
- small magnifying lens
- optional: weight scale capable of measuring in fractions of an ounce or gram.
Water will saturate the sand rapidly and excess water will quickly flow through the pot into the jar. Silt will saturate a little more slowly. Clay will take the longest.
Conclusions: Sand wets rapidly, but holds the least water, allowing most of the application to flow quickly into the jar. Silt wets slightly slower, but holds more water. Clay soils wet slowest, but hold the most water.
Activity 2: Comparing the efficiencies and irrigation time of gravity flow, sprinkler and micro-irrigation systems
In addition to soil types there are several other factors which affect the choice of irrigation method. Labor and equipment cost, water costs, crop selection and topography all must be considered before a farmer implements an irrigation system. The following activit