The delivery system for supplemental irrigation of nursery crops may be permanent, semiportable, or portable. The choice of system is usually determined by the frequency and duration of its use. Where the same species are grown repeatedly and the amount of rainfall is predictable, a choice is made easily. Arid regions are likely to require permanent systems due to the need for regular irrigation. Nurseries in temperate or subtropical areas may receive enough rainfall to maintain healthy field production and only need supplemental water for container areas or newly transplanted field crops.
The three degrees of permanency can be compared as follows.
1. Permanent irrigation system
• The power source is either an electric or a diesel engine. It is permanently installed at the site.
• The pump is also permanently installed and is usually either a deep-well turbine or a horizontal centrifugal one. The deep-well turbine is used when water must be lifted to a height of twenty feet or more.
• The system must be near the water supply and on a solid and level base.
• The main and lateral water lines are stationary and below ground (deep enough to permit crop cultivation above them).
• The lines are constructed of concrete or PVC piping.
• The system is the most expensive to install but least timeconsuming to operate.
2. Semiportable irrigation system
• The power source may be an electric or a diesel engine. It is permanently installed at the site.
• The pump is also permanently installed and is usually either a deep-well turbine or a horizontal centrifugal one.
• The system must be near the water supply and on a solid, level base.
• The main water lines are stationary and below ground with surface couplers for the attachment of portable lateral lines.
• The main lines are constructed of concrete or PVC piping. The lateral lines are usually of PVC.
• The system is less expensive to install but more timeconsuming to operate than a permanent system.
3. Portable irrigation system
• The power source is usually a gasoline engine, transported to the site on a flatbed truck or a PTO (power takeoff) shaft on a tractor.
• The pump is transported on a truck or cart with the power source.
• All water lines are portable and light-weight. They are not buried and are constructed of either PVC or aluminum (Figure 21-5).
• The system is the least expensive to install but most timeconsuming to operate.
As the irrigation water leaves the pump and water lines, it is distributed to the crop through sprinkler heads. Container nurseries use overhead sprinklers or a PVC tube spaghetti system (described in Chapter 20). The sprinkler systems are more wasteful of water than the tube system, which applies water directly to each container and not in between. Either method requires occasional hand-watering. In one case, some plants are not reached fully by the sprinklers. In the other case, the thin
figure 21-5. This supplemental irrigation system delivers water to each pot. It requires exact spacing of each container. (Delmar/Cengage Learning)
PVC tubes occasionally become plugged. The use of filters in the water lines can reduce the frequency of plugging. Some growers also insert a fiber mulch ring around each containerized plant to retain moisture and discourage weeds.
Field production areas may apply supplemental irrigation from rotating sprinklers coupled to the lateral water lines (Figure 21-6). Portable systems may make use of a traveling sprinkler that carries its own water supply and dispenses it rapidly as it is pulled down the nursery rows. Neither system should apply the water faster than the field soil can absorb it.
figure 21-6. A rotating sprinkler system on two different levels keeps this container production area irrigated. (Delmar/Cengage Learning. Photo by Jack Ingels.)
figure 21-7. Trickle irrigation systems permit some movement of the containers. They sometimes plug up, requiring the grower to clear the tube. (Delmar/ Cengage Learning. Photo by Jack Ingels.)
In production fields where crops are widely spaced, as with large trees or high-value specimen plants, supplemental water may be applied through trickle irrigation (Figure 21-7). The low-pressure tube system reduces the waste and expense of watering expanses of field where the moisture is not needed. Instead, water is applied slowly to the root zone of each plant that allows for both optimum growth and cost efficiency. Trickle systems require a timer to turn on the irrigation water each day when the plants are most in need of it. They also require a flow regulator and pressure-compensating emitters to control the rate of water delivery to each plant.