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Irrigation—Principles & Practices

Unit 1.5 | Part 1 – 215
Lecture 2: Irrigation Scheduling & Delivery Systems

• Relatively low cost, readily available, and can be operated with little technical
  background


• Although vulnerable to the wind, oscillators may be useful when “rough irrigating”
  large blocks of garden beds, e.g., prior to planting cover crops, and when irrigating
  large garden spaces

iii. Drawbacks

• Relatively low uniformity of water distribution and high rates of evaporation,
  especially in hot and/or windy situations (see below for more on distribution
  uniformity, or DU)


• Can take time to adjust and “dial in” to provide full, even coverage of the desired
  area without also delivering water beyond the boundary of the desired irrigation
  set


• Inconsistent distribution pattern and vulnerability to wind redistribution;
  neighboring crops may be subject to “drift” and thus increased disease incidence if
  they are prone to fungal disease of the leaf canopy


• Can be difficult or time consuming to accurately determine output/distribution,
  thus leading to over- or underwatering. For example, the adjustability of
  oscillators means the same device could water a 4’ x 12’ section or a 30’ x 30’
  section. So an irrigation set of the same duration will deliver very different
  amounts to these two garden plots.


• Quality of oscillator brands—their useful lifespan, adjustability, and distribution
  uniformity—varies widely, and it can be difficult to know quality until you’ve
  invested considerable time and energy

2. Drip irrigation

a) Drip irrigation has many advantages over sprinkler or flood irrigation, including
application uniformity, the ability to apply water exactly where it is needed, and the
potential reduction of disease and weed incidence in irrigated systems

b) Drip irrigation refers to both rigid ½ inch poly tubing with inline emitters and the thin
wall tubing commonly referred to as “drip tape.” Drip tape is available in an assortment
of wall thicknesses and emitter spacings and is relatively low cost, but also much less
durable compared to the rigid poly tubing.

c) Drip tape is commonly used in small-scale vegetable production systems as a means of
conserving water and minimizing weed and disease pressure

d) Depending on the water source, drip tape and tubing often require filtration to limit
clogging of emitters

e) Drip tape and poly tubing with inline emitters require pressure regulation to optimize
application uniformity

f) Drip tape and poly tubing with inline emitters require a grade of 2% or less and runs of
no more that 300 feet for optimum distribution uniformity

g) Careful consideration must be given to design when setting up a drip irrigation system
to optimize distribution uniformity and system function

G. Environmental Factors Influencing the Type of Irrigation Used

1. Climate and incidence of plant pathogens (see also Unit 1.9, Managing Plant Pathogens)

a) Overhead irrigation may encourage the growth and spread of certain plant pathogens
on crops in certain climates (e.g., Phytopthora spp. on melons, cucumber, peppers, and
tomatoes along coastal California).