Irrigation—Principles & Practices
Part 1 – 214 | Unit 1.5
Lecture 2: Irrigation Scheduling & Delivery Systems
- Over application of irrigation water has the potential to germinate weed seeds that would
have otherwise remained dormant in the soil, leading to higher labor costs for weed
removal and/or significant crop competition resulting in decreased yields - Overapplying water can lead to unnecessary nutrient leaching, soil compaction, decreased
water infiltration rates, erosion, and nutrient leaching (see Supplement 5, Nitrate
Contamination of Groundwater)
F. Irrigation Delivery Systems (see also Appendix 9, Irrigation System Components)
- Sprinklers
a) Micro sprinklers
i. Micro sprinklers are commonly used in small-scale orchards and vineyards
ii. Micro sprinklers are commonly used in garden-scale production systems that require
frequent, light irrigation to help germinate small seeds
iii. Micro sprinklers provide uniform application of water and the relatively small droplet
size minimizes soil surface crusting and aggregate dispersion
iv. Small droplet size is not optimal for distribution uniformity (DU) or water use
efficiency in windy areas
b) Hand-moved aluminum pipe with impact or rotator type heads
i. Hand moved aluminum irrigation pipe is the most commonly used sprinkler
irrigation delivery system in both small- and large-scale farming operations due to
relatively low cost, long life, ease of use, and durability
ii. Hand moved aluminum pipes typically use 3-inch diameter lateral lines with a
3-gallon-per-minute (GPM) sprinkler head mounted on an 18” riser on each 30’ long
section of pipe. Lateral lines are typically spaced either 30’ or 40’ feet apart.
iii. Aluminum sprinkler pipes fitted with impact heads typically require an operating
pressure of at least 45 psi for optimum uniformity. Rotator type heads require higher
pressure.
c) Hand-moved PVC “riser system” for garden-scale applications
i. A simple-to-build, portable riser system of PVC and micro sprinklers can serve the
same purpose as hand-moved aluminum pipe at a garden scale (see Appendix 9)
ii. Because it has fixed spray patterns of 180º and 360º at a pre-determined distance,
the riser system can be sized to suit your garden’s scale and design, assuming basic
irrigation knowledge and access to a standard irrigation supply store
iii. The pattern and uniformity of distribution are relatively consistent and predictable,
and the system can be run with minimal attention to water pressure
iv. Spray distribution, while still gentle on surface soil structure, is delivered in relatively
large drops and risers are only 15”–18” tall, so loss of uniformity and evaporation due
to wind exposure is minimized
v. The riser system can be used to germinate seeds, to grow overhead irrigation-loving
or tolerant crops and low-growing crops to maturity, and can be used to pre-irrigate
and flush weeds in smaller areas. In the absence of timely rains, the riser system can
also be used to establish cover crops and until cover crop height exceeds the height
of the risers.
d) Oscillators
i. Oscillating sprinklers are often used in garden settings, and are a relatively low-cost,
easy-to-use water delivery system
ii. Advantages of oscillators
- Offer large degree of coverage size and pattern flexibility in a single unit