Water Management in Turf

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Water Management in Turf

• Daniel C. Bowman

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The early bird may get the worm, but its the
second mouse that gets the cheese
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Why Manage Water?

• It is only prudent that all turf managers assume
  a proactive posture and become good stewards of
  everyones water resources. If we learn how to
  effectively and intelligently manage our water
  supplies, there should be enough for everyone.
  What do we need to know to achieve this?

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Background

• Americans use 2000 gal/day, compared to 12
  gal/day in undeveloped countries
• One egg uses 40 gal
• One ear of corn, 80 gal
• One pound of hamburger, 2500 gal
• One automobile, 100,000 gal

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Background

• Americans use 2000 gal/day, compared to 12
  gal/day in undeveloped countries
• One egg uses 40 gal
• One ear of corn, 80 gal
• One pound of hamburger, 2500 gal
• One automobile, 100,000 gal

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Background

• 97 of the worlds water supply is in the oceans
• 2 is in polar ice caps
• Only 1 of the total is fresh water!

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Background

• Water is neither created or destroyed. Your cup
  of coffee this morning may have contained water
  molecules that Cleopatra bathed in.
• Given that, location and timing become crucial
  elements of water allocation.

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What We Need To Know

• 1. How water behaves in different soils
• 2. How and why turf obtains water from the soil
• 3. How the plant uses and loses the water it
  obtains
• 4. How the manager can irrigate most efficiently
  to replace water lost

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Water In The Soil

• Whether water is supplied through rainfall or
  irrigation, it can only be effective when it is
  able to infiltrate into the soil. Unfortunately,
  large amounts of water can be lost through
  surface runoff. How much depends on the type of
  soil, the topography, the moisture content, the
  precipitation or irrigation rate, and the
  presence of vegetation.

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Water In The Soil

• It makes sense to try to minimize runoff losses
  by improving soil structure, contouring for
  gentle slopes, matching irrigation to
  infiltration, and maintaining a good turf cover.

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Water In The Soil

• Once water has entered the soil, it tends to fill
  most empty pores, both macropores and micropores.
  Water continues to move downward, under the
  force of gravity, through the macropores.
  Eventually the macropores drain completely, and
  are refilled with air. Micropores, on the other
  hand, retain their water against the force of
  gravity. This is because water is both adhesive
  and cohesive.

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Water In The Soil

• Micropores arent all one, uniform size. They
  range from relatively large to very tiny. The
  force with which water is held in the pores is
  related to the pore size. Larger pores have just
  enough force to hold the water against gravitys
  force, but not enough force to resist the force
  of roots to obtain water. The small pores hold
  on to their water very tightly, much more tightly
  than the force of gravity, and often more tightly
  than the force of the root to extract water from
  the soil.

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Saturation

• This means that only some of the micropores give
  up their water to the plant. Some retain their
  water even though the plant may be wilting from
  drought. We can thus identify several values
  with regards to soil moisture. The first is
  completely saturated, when all the pores are
  filled, as during a heavy rain. This may
  represent about 50 of the total soil volume

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Field Capacity

• After drainage has removed the water from the
  macropores, the soil is at field capacity, with
  water occupying perhaps 30-35 of the total
  volume. But the soil doesnt stay at field
  capacity very long.

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Permanent Wilting Point

• Evaporation of water from the soil surface and
  absorption by plant roots start to deplete the
  water from the larger of the micropores, and the
  soil begins to dry out. After a while, the plant
  can no longer remove water from the smallest
  pores, and it starts to wilt. When the plant can
  no longer recover, even if irrigated, the soil is
  considered to be at the permanent wilting point,
  which may occur when soil water is around 10-15
  of the total volume.

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Available Water

• The difference between field capacity and
  permanent wilting point is the amount of
  available water. Take the case where field
  capacity is 35 and the permanent wilting point
  is 15. The difference, 20, is the amount of
  water, expressed as a percent of total volume,
  which is potentially available to the plant. We
  can use this to guestimate the amount of water
  available in a given rootzone.

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Effective Available Water

• Water has to be both available to the plant, and
  in the rootzone, to be of any use to the plant.
  Water that percolates past the rootzone is lost
  to the plant, just as runoff is wasted.
• The rootzone is thus critically important!

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How Much Water is in Soil?

• Consider a bermudagrass root system which reaches
  a depth of 15 inches in the soil. We can
  multiply 15 inches by 20, giving us 3 inches of
  available water. This would probably be enough
  for 8-9 days in the summer, as will be discussed
  below. The bermudagrass root system would have
  access to around 3 inches of water, assuming the
  soil were at field capacity.

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How Much Water is in Soil?

• Now consider a bentgrass fairway, with a root
  system 6 inches deep in May. Multiplying 6
  inches by 20 gives us 1.2 inches of available
  water. This would be enough water for around 4
  days. Finally, lets consider the same bentgrass,
  but during the heat of August when the root
  system has decayed to only the top 2 inches of
  soil. Two inches multiplied by 20 give 0.4
  inches of water, about enough for one day.

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Soil Textural Class Affects How Much Water is
Held by Soil
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Changes in Soil MoistureCan you guess what is
happening?
Soil H2O
Time
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Localized Dry Spots (LDS)

• Water wont infiltrate, just sits on the surface.
• Caused by hydrophobic conditions which develop at
  or near the soil surface
• Similar to a waxy coating on the individual soil
  particles - Oil and Water dont mix!

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Localized Dry Spots (LDS)

• Usually worse in sandy soils
• Spotty, random distribution
• Wetting/drying cycles make it worse

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Coated Sand Grains Repel Water
H2O
H2O
Uncoated Sand Grain
Coated Sand Grain
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Hydrophobic Soils
H2O
H2O
Hydrophobic
Dry Soil
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Coping with LDS

• Avoid allowing soil to dry out
• Cultivation or topdressing may help by mixing
  hydrophobic soil with unaffected soil
• Most common method is by using wetting agents

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Wetting Agents

• Similar to soaps, but they are not designed to
  remove the waxy coating, only mask it so that
  water doesnt know the wax is there.
• On small areas, can use Joy detergent mixed with
  water 11000
• For big areas, numerous commercial products

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Wetting Agents

• Can improve turf quality, root growth by
  maintaining adequate soil moisture
• May reduce total water use, which will save
• Increased infiltration can mean less down time
  due to standing water

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Surfactant Molecules
Polar Head (attracted to H2O)
Non-Polar Tail (attracted to oil, wax etc)
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Wetting Agents
Surfactant Molecule
H2O
Waxy Coating on Sand Grain
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Plant Water

• Plants require water for one major reason and one
  minor reason. The vast majority of water the
  plant absorbs from the soil is actually lost as
  water vapor from the leaves, to the atmosphere,
  by the process of transpiration. Transpiration
  occurs through the leaf stomates, and is very
  important because it cools the leaf.

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Plant Water

• If not for transpirational cooling, a leaf could
  reach a temperature of 120o F during midsummer.
  This temperature would easily kill most plants.
  Fortunately, transpiration keeps leaf
  temperatures much cooler, usually below 90o. A
  small amount of water that is absorbed is
  actually used to build new tissues, but for every
  ounce of water used to fill up new tissues,
  around 300-400 ounces of water are lost to the
  atmosphere.

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Plant Water

• Roots absorb water from the soil and transport
  the water to the shoot through the xylem. But
  how? We understand about the force of gravity
  pulling water out of the macropores, but how does
  a root exert a force on water to pull it out of
  the micropores? To understand how this happens,
  we need to understand a few rules about water.

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Plant Water

• First, water runs downhill. It flows from a
  position of high energy (the top of the hill) to
  a position of lower energy (the bottom of the
  hill). Sometimes there arent any hills
  involved, but water can still exist in high
  energy and low energy states. This is the case
  in the soil/root environment.

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Plant Water

• Soil water at field capacity can be considered
  fairly high energy. The water in a root is
  fairly low energy. Thus, there is a natural
  tendency for water to flow from the soil and into
  the root. How does it get to the shoot?

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Plant Water

• The second rule about water is that it is sticky.
  It sticks to itself, which is called cohesion.
  Consider what happens when you suck water through
  a straw, even a real long one. The water is
  pulled up against the force of gravity, in a
  continuous column.

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Plant Water

• The force to pull the water is the vacuum, or
  negative pressure, created by your mouth. All
  the water behind the leading edge is sticking
  to the water in front of it, and being pulled
  along. This ability to pull long columns of
  water up, against gravity, is fundamental to
  getting water up inside a plant.

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Plant Water

• It may be helpful to think about all the water in
  a plant as part of one gigantic mega-molecule.
  All the water is connected because water sticks
  to the adjacent water. Plants lose water through
  their stomates as a gas. This is like sucking on
  a straw. The water lost through the stomates
  exerts a pull on the mega-molecule in the plant.
  In other words, transpiration gives the rest of
  the water in the plant a little tug.

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Stomata
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The Stomatal Cavity
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Plant Water

• There is one big continuum of water from the
  soil, through the root, up the stem, and into the
  leaf. When you tug at one end, the other end
  feels the tug. Eventually the soil water may be
  nearly depleted, approaching the permanent
  wilting point. At this point, the plant is
  unable to get soil water to move quickly to the
  root, no matter how hard it pulls. Water is
  still being lost through the leaves, but isnt
  being replaced from the soil. The result is a
  water deficit, or wilting.

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Plant Water Potential

• ? is symbol for water potential
• ?plant ?osmotic ?turgor
• -6 bars -8 bars 2 bars

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Water Moves from Higher to Lower Potentials
-1000 bars
Air
Shoot
-6 bars
Root
Well-Watered Conditions
Soil
-4 bars
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Soil Water Potential MayLimit H2O Uptake
-1000 bars
Air
Shoot
-12 bars
Root
Drought Conditions
Soil
-18 bars
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Drought Symptoms

• Curling of leaves in some species
• Gray or blue color develops
• Footprinting
• Wilting
• Death

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Coping with Drought

• Avoidance
• Tolerance
• Escape

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Avoidance

• Usually the first response. Plants adapt to
  avoid internal water deficits - eg. Deeper, more
  extensive roots to absorb more water, closing of
  stomates or thicker cuticles to reduce water loss.

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Tolerance

• When water deficit does occur in the plant, some
  have the ability to tolerate it. They do this by
  maintaining turgor pressure in the cells via
  osmotic adjustment. This is probably secondary
  in importance in turf.

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Escape

• Annual species avoid drought altogether by
  surviving the period as a seed. Some warm season
  grasses, and KBG can survive extended periods in
  a dormant condition.

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How Much Water Does Turf Use?

• It depends on the environment, the turf species,
  management practices, and soil moisture.
  Environmental factors that control water loss
  (evapotranspiration) are
• Temperature Relative Humidity
• Wind speed Light Intensity
  (Radiation)

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How Much Water Does Turf Use?

• Water use rates are usually expressed in inches
  or cm of water lost per day. In general, the
  warm season grasses use less water than the cool
  season grasses.

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How Much Water Does Turf Use?
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How Much Water Does Turf Use?

• How do we determine water use? There are a
  number of methods used to estimate how much water
  a turf requires at any given time, under any
  given environment. One of the most common
  methods was discussed above, where environmental
  data are used to calculate a theoretical, or
  reference water use. This value is referred to
  as ETp, or potential evapotranspiration, and it
  is used as a reference point.

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Automated Weather Stations
Both measure -Temperature - Wind - Rel.
Humidity - Light
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How Much Water Does Turf Use?

• Another method is the Atmometer, a simple,
  inexpensive device that mimics a leaf canopy to
  estimate ET.

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Atmometer
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How Much Water Does Turf Use?

• There are also a number of soil moisture sensors
  on the market, including
• tensiometers
• gypsum blocks
• solid-state sensors
• Aquaflex

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How Much Water Does Turf Use?

• Most of these measure soil moisture at one point,
  in a single, small volume of soil. This means
  that it might not be very representative of the
  overall soil moisture.

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How Much Water Does Turf Use?

• Aquaflex is a new product, which we are
  evaluating at NCSU. It consists of a 10 long
  cable which is buried in the rootzone, at
  approximately 6. It has the advantage that soil
  moisture is measured and averaged over a much
  larger soil volume.

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Slit and Sensor
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Inserting Sensor
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Sensor in Valve Box
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Taking a Reading
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Irrigating Between the Lines
Field Capacity
Refill Level
Perm. Wilt Pt.
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How Much Water Does Turf Use?

• Actual turf water use usually isnt quite as high
  as ETp. We use a factor, called the crop
  coefficient (Kc), to relate ETp to actual turf
  ET. A crop coefficient remains fairly constant
  for a given species during a given season, but
  varies considerably between species and between
  seasons. It is useful, however, if we have
  enough previous data for crop coefficients for a
  given species.

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How Much Water Does Turf Use?

• For example, we know that the Kc of bermudagrass
  is about 0.7. This means that bermudagrass will
  use about 70 as much water as is predicted using
  environmental data to calculate ETp. If our
  environmental data tells us that a reference crop
  used 2.2 inches of water for a given week in the
  summer, we can multiply 2.2 by 0.7, giving us
  1.54 inches of water actually used by the
  bermudagrass.

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Water Use

• These calculations assume there is adequate water
  in the rootzone. Mild to moderate drought stress
  may reduce actual ET. For example, if
  bermudagrass is grown under continuous, moderate
  water stress, the turf will easily survive, yet
  actual ET might only be 0.55-0.6 of Etp.

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How To Manage Water

• Based on what weve just discussed, we now have
  enough information to schedule our irrigation.
  We need to know how much water our particular
  turf is using, which we will determine using
  reference ET from a weather station/computer
  system plus a crop coefficient specific for our
  turf species. We also need to know where the
  roots are in the soil profile, at least roughly.
  Finally, we need to know how much available water
  can be held by our soil.

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How To Manage Water

• Basically were going to treat our water like a
  bank account, where we have inputs (deposits),
  outputs (withdrawals), and a certain amount of
  water in the soil (standing balance). We just
  follow the flow of water (money) into and out of
  the system. In our case, the system is the soil
  in the rootzone. If the roots go down 12 inches,
  our system is the water held in 12 inches of
  soil. If the roots go down only 2 inches, our
  system is the water held in that 2 inches.

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How To Manage Water

• We start with our soil at field capacity. If our
  4 inch root system holds 0.9 inches of available
  water, thats what we have to start. The weather
  station data tells us that over the first three
  days, 0.8 inches of water are used by the
  reference crop. We apply our Kc of 0.7 for
  bermudagrass (assuming thats the grass being
  grown) and find that our turf actually used about
  0.56 inches of water.

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How To Manage Water

• Subtracting this from the original 0.9 inches of
  available water, we find that we have about 0.34
  inches of water left. Its time to water, since
  we dont want to completely deplete all the
  available water. How much to irrigate? About
  0.6 inches, to replace the 0.56 lost from the
  system, and have a little left for good measure.
  We have returned the soil to field capacity,
  without irrigating excessively and wasting water.
  What do we do if it rains?

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Conduct a Water Audit

• Observe system for obvious problems Using water
  meter data and turf area, calculate average rate
• Canning the turf
• to determine application rate
• to determine distribution, uniformity
• to identify problem heads

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Canning an Athletic Field
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Canning an Athletic Field
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Canning an Irregular Turf Area
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Canning the Turf

• Run irrigation system for set time
• Measure depth of water in cans
• Average the measurements
• Calculate irrigation rate
• Average Depth/Time Rate
• 0.6/30 minutes 0.02/minute
• 0.02 in/min X 60 min/hr 1.2 inches/hour

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Irrigation Uniformity Critical to Saving Water
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Ideal Uniformity
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Actual Uniformity
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Over Irrigation to Compensate
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Center For Irrigation Technologyhttp//cati.csufr
esno.edu/cit/