Module 4 – Turfgrass Cultural Practices
Lesson 3 – Irrigation
Lesson Title - What are the necessary cultural practices that keep turfgrasses healthy?
Overview
Turfgrass growth and health depends on the correct use of cultural practices.
Therefore, it is important for students to understand irrigation and how it contributes to
the overall health and maintenance of turfgrass.
Objectives:
Describe the purposes of irrigation for turfgrass areas
Explain turfgrass irrigation requirements
Determine irrigation frequency and amount
Compare how different soil textures affect water availability
Identify irrigation parts
Assess sprinkler distribution patterns
Additional Readings:
Turgeon, A. J. (2007). Turfgrass Management. Upper Saddle River, NJ: Simon &
Schuster.
Puhalla, J., Krans, J., Goatley, M. (1999). Sports Fields. Hoboken, NJ: John Wiley &
Sons, Inc.
Residential Sprinkler System Design Handbook: A Step-By-Step Introduction to Design
and Installation – Hunter Industries (link to pdf)
Conducting and Irrigation Audit – STMA (link to pdf)
Turfgrass cultural practices are all the methods used to maintain healthy turfgrass. The
third cultural practice that will be covered is irrigation.
Turfgrass plants need water to survive. Plants access moisture through precipitation,
irrigation, and capillary flow. Plants lose moisture through evaporation, transpiration,
and drainage.
Precipitation (P) and Irrigation (I)
– Precipitation and irrigation
events provide water to supplement
plant growth.
Drainage (D) – As water drains
through the soil profile, it becomes
unavailable to plants.
Evaporation (E) and Transpiration
(T) – Plant roots are unable to
access water if it is evaporated
from the soil. Transpiration, water
lost from plant parts, also reduces
plant-available water.
Capillary Flow (CF) – Water
moves within the rootzone to
provide moisture to plants.
Graphic: A. J. Turgeon, Ph.D.
To aid precipitation and capillary flow, and make up for what is lost to evaporation,
transpiration, and drainage, water is supplied to turfgrass areas via irrigation systems.
Irrigation is important for healthy turfgrass growth due to the following reasons:
- Helps maintain turf’s green color
- Necessary for photosynthesis
- Modifies turfgrass tissue temperatures on hot days
- Aids plant rigidity
- Decreases weed encroachment
- Improves tolerance to insect and disease pressure
- Washes in fertilizers and some pesticides following application
- Maintains sufficient surface moisture to promote germination of turfgrass seed
Turfgrass should be watered on an as needed basis. In general, turfgrasses require 11.5 inches of water per week, minus any rainfall, during their active growing period to
remain healthy and resilient. Soil texture, compaction issues, rootzone depth, and
infiltration capacity all influence the frequency of irrigation events and the amount of
water that is applied. Other special considerations, such as weather and climatic
conditions, timing, and soil moisture tools, will assist in the planning of irrigation events.
Soil Texture
As discussed in Unit 3, soil texture is the size of the particles that make up a soil. Sand
is the larger size of particles, silt is moderate in size, and clay is the smaller size of
particles. Particle size affects drainage and water holding capacity within the soil and
determines the rate at which water drains through a saturated soil.
Determining the predominant particle size of the rootzone will assist in planning
irrigation duration and the volume of water to apply. Water typically moves more freely
through soil high in sand than it does through soil high in clay. Due to coarser texture,
sand has larger pore spaces between particles compared to finer textured soil. Large
pore spaces may allow for increased water movement in the rootzone, but coarse
textured soil is more likely to lose water to drainage and evapotranspiration following
irrigation. Fine textured soils retain water and are not as susceptible to water loss from
drainage and evapotranspiration.
Water moves quickly through
predominantly sandy soils due
to large pore spaces. Water
reaches plant roots quickly, but
also drains or is evaporated
from sandy soil quickly.
Graphic: A. J. Turgeon, Ph.D.
In finer textured soils, water
movement slows down due to
smaller pore spaces. Small
pore spaces retain more
water when compared to
large pore spaces.
Graphic: A. J. Turgeon, Ph.D.
Soil Texture Comparison
Coarse-textured
Fine-textured
Graphic: A. J. Turgeon, Ph.D.
Soil Texture Effects on Water Availability
Coarse-textured
- Large pore spaces
- Poor water retention
- Fast water infiltration
- Rapid drainage
VS.
- Water can be applied
more rapidly due to higher
infiltration
Fine-textured
- Small pore spaces
- High water retention
- Slow water infiltration
- Slow drainage
- Lower volume of water
can be applied to account
for slower infiltration
Soil Compaction
Compaction was also covered in Unit 3. Soil compaction results from soil particles
being packed together when topsoil is compressed due to foot or vehicular traffic. If
soil is compacted, water movement into and within the soil is severely restricted. As a
result, water collects on the soil surface or runs off the surface and plants are unable to
access the water necessary for healthy growth. Soils that are more prone to
compaction include finer textured soils such as clay, silty clay, and sandy clay. Soils
that are less prone to compaction include coarse textured soils such as loamy sands
and sands. Highly compacted soil impedes infiltration and percolation of water in the
soil and thereby reduces the effectiveness of irrigation.
Rootzone Depth
Knowing the depth of the rootzone helps determine amount and frequency of irrigation.
Deep, infrequent irrigation that wets the entire rootzone (generally 4 inches in depth)
leads to the healthiest turfgrass plants. Plants develop deep, strong root systems that
can extract water from a large volume of soil. Turfgrass plants with deep root systems
are better able to withstand environmental and mechanical stress and have increased
recuperative capacity.
Watering turfgrass areas lightly and frequently leads to weak, unhealthy plants,
promotes a shallow root system, and increases probability for disease, algae, and moss
development. Light and frequent irrigation should be reserved only to support seed
germination and initial growth. As seedlings mature and develop deeper root systems,
light and frequent water applications are gradually scaled back to deep and infrequent
water applications.
Graphic: A. J. Turgeon, Ph.D.
Infiltration Capacity
When irrigating, the rate of water application should not exceed the infiltration capacity
of the soil. When infiltration capacity is exceeded, water will either collect on the
surface and puddle or runoff.
1
2
Water application rate is exceeding
infiltration rate, which leads to
standing water on the surface (1)
and/or water running off the
surface to a drainage area (2).
Graphic: A. J. Turgeon, Ph.D.
PR < IC
When precipitation rate (PR) exceeds
infiltration capacity (IC), water is unable
to infiltrate into the soil and will either
collect on the surface or runoff the
surface. If water does not infiltrate the
soil, plants cannot access the water
needed to support healthy growth.
When infiltration capacity (IC) exceeds
precipitation rate (PR), the amount of
water being applied to the soil is lower
than the rate water is being absorbed by
the soil. The ideal situation when
applying water to any turfgrass surface is
for infiltration capacity to exceed
precipitation rate.
PR > IC
Graphic: A. J. Turgeon, Ph.D.
Additional Considerations When Irrigating
Weather and Climatic Conditions
Weather conditions affect the amount of water needed to sustain healthy turfgrass. High
air temperature, low relative humidity, wind, and sunny conditions increase the amount
of water lost by a turfgrass plant. Transpiration and evaporation rates influence the total
amount of water required by plants for healthy growth. More frequent irrigation is
needed to make up for water lost to evapotranspiration.
In drought conditions, turfgrass areas that do not have access to irrigation can be
allowed to go dormant. Turfgrass recovers from dormancy as long as traffic is very
limited.
Timing
Irrigation can be performed anytime day or night. However, early morning, between
4:00 am am and 9:00 am, is the best time to water turfgrass plants due to reduced
water lost to evaporation, less sunlight, and lower wind velocity. There is also reduced
disease potential by minimizing the duration of leaf wetness. Watering at midday is not
recommended, as water lost to evapotranspiration is at its greatest potential. Midday
watering can be effective if the goal is to temporarily cool plant temperatures and
reduce heat stress. Irrigating should be avoided during the evening and at night.
Excessively wet plants in the evening can remain wet throughout the night and create a
favorable environment for fungal diseases.
Overwatering
Applying too much water to turfgrass plants can be detrimental.
include:
- Poor turfgrass health
- Increased weed, disease, and insect problems
- An open, sparse stand invaded by moss and/or algae
- Reduced wear tolerance, vigor, and climatic-stress tolerance
- Increased compaction under traffic due to wet, soft soil
- Reduction of oxygen availability to plant roots
- Runoff and/or leaching of nutrients and pesticides
Negative effects
Graphic: A. J. Turgeon, Ph.D.
Handwatering
Some turfgrass areas may be prone to drying out more quickly than other areas.
Supplemental irrigation can occur by handwatering, and is favorable for extending the
interval between irrigation events. Handwatering is effective for spot treating small
areas.
Photo: A. J. Turgeon, Ph.D.
Syringing
Syringing is a very light application of water applied to the turf leaf surface that cools the
turf so it can get through the hottest part of the day. Syringing is different than watering
as it does not restore soil moisture. When evapotranspiration exceeds the rate water is
being absorbed by roots, wilt can develop because of a moisture deficit within the plant.
Wilt is characterized by folded or curled leaves, blue-green color, and visible footprints
left after walking on the surface. This can happen on soils with adequate water.
Syringing is done to correct plant water deficits, reduce plant tissue temperatures, and
remove substances from the leaves. Syringing usually takes place at midday. Wilted
turf recovers quickly if it is watered immediately.
Soil Moisture Tools
Tools are available that measure consumptive water use and soil moisture.
Consumptive water use is estimated by measuring evapotranspiration. Consumptive
water use depends on temperature, wind, relative humidity, and other environmental
factors.
Evaporation pan – Graphic: A. J. Turgeon, Ph.D.
An evaporation pan can be used to measure evapotranspiration. Water is placed in a
pan in an unshaded area. Evaporation from the pan approximates evapotranspiration.
Irrigation events can be scheduled according to the water lost from the pan.
What do you think – will the evapotranspiration rate be high or low on a hot, windy, low
humidity day? (click for answer)
High
Will the evapotranspiration rate be high or low on a cloudy, cool, humid day? (click for
answer)
Low
Soil moisture measurements are taken with tensiometers. These devices are inserted
at different depths in the ground. As the soil dries, the tensiometer gives a reading that
indicates reduced plant available moisture.
Graphic: A. J. Turgeon, Ph.D.
Irrigation Systems
Carrie – there is a big activity I’m working on that I would like to place here. Hopefully I
will be able to send that to you next week.
When an irrigation system is operating at the correct pressure, optimal water distribution
from each sprinkler head forms a wedge-shaped pattern.
Graphic: A. J. Turgeon, Ph.D.
Graphic: A. J. Turgeon, Ph.D.
Water application from one sprinkler head is not uniform. The amount of water applied
per unit area decreases toward the periphery of the area of coverage, which forms the
wedge pattern. The wedge pattern indicates correct pressure and application of water.
As a sprinkler head rotates, the area covered at each increment along the radius
increases as the distance from the sprinkler increases.
The center circle (a) has the smallest area and receives
the most amount of water. The outermost circle (e) has
the largest area and receives the least amount of water.
Graphic: A. J. Turgeon, Ph.D.
To ensure sprinkler heads are working correctly and delivering the correct amount of
water, an irrigation audit can be conducted. Rain gauges are set up in increments to
measure water output and ensure a wedge pattern. The amount of water collected is
recorded on a chart that indicates distance from the sprinkler head and amount of water
collected at each increment. The wedge pattern is desirable.
Photo: A. J. Turgeon, Ph.D.
Graphic: A. J. Turgeon, Ph.D.
Click here for more information on how to conduct an irrigation audit. (insert irrigation
audit pdf)
Low pressure in the irrigation system results in streams of water that do not break up
sufficiently for wedge shaped distribution.
Photo: A. J. Turgeon, Ph.D.
Water is concentrated into one
area more than others.
Graphic: A. J. Turgeon, Ph.D.
Low water pressure from sprinkler heads results in a donut shaped pattern.
Photo: A. J. Turgeon, Ph.D.
High pressure is also undesirable. High pressure causes finer water droplets which can
be affected by wind drift.
Photo: A. J. Turgeon, Ph.D.
High water pressure results in an irregular and unpredictable pattern.
Graphic: A. J. Turgeon, Ph.D.
Compare the distribution patterns between high pressure, low pressure, and correct
pressure. Match the picture to the correct pressure. (make this a matching exercise?)
High
Low
Correct
Graphic: A. J. Turgeon, Ph.D.
At correct pressure, a wedge-shaped pattern is created with the innermost part of the
circle receiving the most water and the periphery of the circle receiving the least amount
of water. To account for decreased coverage at the edges of the circle, sprinkler heads
are strategically placed to overlap. This is commonly referred to as head-to-head
coverage.
Graphic: A. J. Turgeon, Ph.D.
The wedge-shaped pattern overlaps to deliver a uniform amount of water to turfgrass
areas.
Take a golf course green as an example. Due its irregular shape, sprinkler heads must
be strategically placed so the green receives optimal coverage and uniform distribution.
Graphic: A. J. Turgeon, Ph.D.
The location of the sprinkler heads form a triangle. Triangular spacing is ideal in this
application because the area of greatest need – the green – is receiving optimal
coverage and uniform distribution.
The outside periphery of the triangle, where sprinkler heads no longer overlap, receives
less water. The color coding represents decreasing water application. The black area,
the center of the triangle and where the sprinklers overlap, receives the most amount of
water. The yellow area, the periphery of the triangle and where sprinklers do not
overlap, receives the least amount of water.
Graphic: A. J. Turgeon, Ph.D.
Golf course greens and home lawns present a challenge for sprinkler placement due to
their irregular shapes. During the irrigation design phase, sprinkler heads should be
located correctly to ensure optimum distribution and avoid dry areas.
Sprinkler head spacing on golf course fairways and athletic fields differ in that they are
usually installed in a line.
Single row spacing can be found on golf course fairways. The blue area represents
sufficient coverage between sprinkler heads. However, coverage decreases towards
the periphery.
Graphic: A. J. Turgeon, Ph.D.
The downfall to single row spacing is that the areas receiving inadequate coverage are
more prone to drying out. In drought conditions, this can lead to the appearance of
waves.
Photo: A. J. Turgeon, Ph.D.
Single row spacing is not ideal for golf course fairways or athletic fields. As with golf
course greens, sprinklers should be installed at appropriate distances so water
application overlaps for uniform distribution in the areas of highest need. Double or
triple row spacing can be utilized to achieve uniform coverage.
Graphic: A. J. Turgeon, Ph.D.
Graphic: A. J. Turgeon, Ph.D.
Test Your Knowledge
Why is it important to irrigate turfgrass areas? (Check all that apply.)
Support active growth
Maintain plant rigidity
Assist with plant cooling
Increase weed, insect, and disease pressure
Maintain surface moisture to encourage seed germination
How do turfgrass plants access moisture?
Irrigation, precipitation, capillary flow
Evaporation, irrigation, precipitation
Irrigation, precipitation, drainage
Irrigation, precipitation, capillary flow, runoff
________ _____________ watering leads to the healthiest turfgrass plants because
plants develop deep, strong roots that can extract water from a large volume of soil.
________ _____________ watering leads to weak, unhealthy turfgrass plants, and
promotes a shallow root system.
Light infrequent; Deep frequent
Light frequent: Deep infrequent
Deep infrequent; Light frequent
Deep frequent; Light infrequent
True or False: The most effective irrigation program does not allow the rate of water
application to exceed the infiltration capacity of the soil.
What are the effects of overwatering?
Increased health and vigor of turfgrass plants
Reduction of oxygen availability to the root system
Higher disease tolerance
Reduced compaction
What is the purpose of a valve in an irrigation system?
Controls the on-off flow of water to sprinkler heads
Determines when and how long sprinkler heads will operate
Prevents the backflow of contaminated water
Maintains pressure throughout the system
What is the ideal connection between the lateral line and sprinkler head?
Main line
Swing joint
Control valve
Valve manifold
The water distribution pattern for a sprinkler head operating at the correct pressure is:
A donut shape
Irregularly shaped
Triangularly spaced
Wedge shaped
An irrigation audit is important because:
It ensures sprinkler heads are working correctly and delivering the correct amount of
water
It allows turfgrass managers to locate all of the sprinkler heads in the system
It assists with the development of a blueprint for irrigation system design and installation
It creates an automated program that turfgrass managers can enter into the controller to
schedule run times
How does sprinkler head spacing compensate for decreased amount of water applied
towards the periphery of the area of coverage?
Spacing between sprinkler heads does not matter.
Single row spacing provides the best solution for uniform coverage on athletic fields.
Sprinkler heads should be strategically placed to overlap and deliver a uniform amount
of water to the areas of highest need.
Sprinkler head patterns should never overlap, as that will lead to overwatering.