Water

Management

Richard L. Duble

Texas A&M University

Rainfall rates vary from less than 10 inches to nearly 60 inches throughout the southeastern states. Turfgrasses require about 60 inches of water to remain green and growing throughout their growing season. Obviously, most areas do not meet that requirement. Thus, grasses

are frequently dormant for long periods under non-irrigated conditions.

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Annual rainfall (inches)

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16 20 24 32 40

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St. Augustinegrass lawns require about 40 inches of rainfall plus irrigation during the growing season (March –October) to remain green.

Buffalograss, the most drought tolerant turfgrass, requires about 30 inches of water during the growing season. Without irrigation, buffalograss remains dormant during most of the summer.

Dormant buffalograss has a uniform straw colored appearance and is not unattractive if weeds are eliminated. Buffalograss can be grown without irrigation in areas that receive 15 to 30 inches of rainfall. In high rainfall areas in the southeast is not competitive with bermudagrass and weeds.

Bermudagrass also requires about 30 inches of water during the growing season to remain green.

Without irrigation, bermudagrass goes into dormancy and turns straw-colored. Bermudagrass can be grown without irrigation in areas that receive 25 or more inches of rainfall.

Centipedegrass, widely used for landscapes in the southeastern states, has about the same water requirements as St. Augustinegrass.

Dormant centipedegrass has a brown appearance, but will survive many weeks without irrigation.

When we examine water requirements for turfgrass survival we find a wide range among commonly used

turfgrasses. Tall fescue, St. Augustinegrass, centipedegrass and Kentucky bluegrass all have a

relatively high water requirement for survival (at least 35 inches). In contrast, buffalograss and

bermudagrass are the most drought tolerant and will survive with 15 to 20 inches of water, respectively.

Water Needs Tall fescue (requires the

St. Augustinegrass most)

“Tif” Bermudagrass

Zoysia

Common Bermudagrass (requires the

Buffalograss least)

Under adequate irrigation or rainfall, grasses appear green and lush.

As water becomes limiting, grasses wilt and show footprinting after walking across the lawn.

As water becomes limiting, grass leaves roll or fold up at mid-day as a means of reducing water loss. The rolled leaves have greatly reduced surface area that are exposed to evaporation.

Within a few days after water stress, leaf tips become chlorotic.

Eventually, the entire lawn takes on a chlorotic or straw-like appearance. The lawn remains dormant until rainfall or irrigation is adequate for the plant to resume growth.

Grass species, fertilization practices, mowing heights, slopes, soil depth, soil type, shade

and turf use all affect water needs by turfgrasses. Thus, the same grass may have significantly different water requirements on different sites. For example, bermudagrass

golf greens require at least 50 inches of water during the growing season, whereas

bermudagrass lawns may remain green with only 20 inches of water.

Water Needs Determined By

Grass species

Management

Site characteristics

Environment

Use

Application Rateand Frequency

Water Use Rate (ET)

Soil Moisture Retention

Infiltration Rate

Effective Depth of Rooting

Water use rates for turfgrasses are best estimated by evapotranspiration (ET) rate on a daily basis. ET rates vary from less than a 1/10 of an inch to ½ inch during a summer day depending on temperature, sunlight, wind and humidity. ET rates also varying dramatically between seasons of the year with daylenght. Typical ET rates for College Station, TX for summer months are 2/10 inch per day.

Water use rates for bermudagrass in College Station vary according to this graph. Obviously, daily fluctuations can be significant. The next graph

represents a 30 year average of water use rates. This information must be

taken into consideration when preparing irrigation programs or when

setting irrigation controllers.

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0J F M A M J J A S O N D

Water Use RateWater Use (in/day)

Bermudagrass

In the next graph note the difference in water use between the maximum rate and the wilting point. This information can be

helpful during periods of water restrictions. So long as the irrigation rate exceeds the wilting point requirement the grass will remain green and growing. The water required at the wilting point is about

60% of the maximum water use rate for warm season grasses.

0.40

0.35

0.30

0.25

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0.1May June July Aug. Sept.

Bermudagrass/Dallas, TX

Available Water (inches/day)

Max. Water Use

Wilting Point

Similar water use requirements are found in cool season

grasses. Usually cool season grasses require about 70 % of

the maximum water use rate to prevent wilting.

0.40

0.35

0.30

0.25

0.20

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0.1May June July Aug. Sept.

Tall Fescue/Amarillo, TX

Available Water (inches/day)

Max. Water Use

Wilting Point

When developing an irrigations program all of these variables must be considered.

Irrigation programs developed around these variables save about 50% of the water required for turfgrass irrigation

compared to programs developed bases on visual observations of water needs.

Water use rates (ET) are published in local newspapers and are available through the internet for locations

throughout the U.S.

Application Rateand Frequency

Water Use Rate (ET)

Soil Moisture Retention

Infiltration Rate

Effective Depth of Rooting

Much of the water from both rainfall and irrigation is lost through runoff, leaching or

evapotranspiration. On heavy clay soils or on sloping sites, runoff accounts for as much as 50% of the water applied. On sandy soils or on soils

with shallow profiles, leaching accounts for significant water losses. The role of the irrigation manager should be to monitor stored water in the

root zone and to replace water used by turfgrasses. Ideally, the root zone should be recharged when

about 60% of the storage capacity is depleted.

ET Precipitation

Runoff

Storage

Leaching

This sandy soil profile holds about 1.5 inches of water per foot of soil. This type profile is common on golf greens and sports fields. Such profiles require irrigation at 3 to 4 day intervals during peak periods of water use.

Watering PracticesWatering practices that take into consideration ET rates and soil profiles are much more efficient than irrigation practices based on visual observations.

Overwatering is common on sports fields, golf courses, and landscapes. One of the major causes of overwatering (or excessive water use) is the non-uniformity of irrigation systems. A properly designed and maintained irrigation system is at best 75% uniform. Inconsistent pressure, irregular sprinkler head spacing, inadequate pipe size and wind all reduce the uniformity of an irrigation system. Water audits on golf courses and sports fields show an average uniformity of about 50%. A uniformity of 50% requires the irrigation manager to apply twice as much water as needed to adequately irrigate the dry areas of a field.

On golf courses and landscapes structures, trees, ornamental beds and other obstacles such as sand traps on golf courses interfere with the spacings of sprinkler heads and leads to non-uniformity.

Water requirements vary significantly between sites depending on the use of each site. For example, on golf courses the golf green requires at least 50% more water than the surrounding slopes. But, usually the same irrigation system waters both sites. Efficiently designed irrigation systems on golf courses have a separate system for the greens and the surrounds.

Similarly, in residential and commercial landscapes ornamental beds have significantly different water requirements than turfgrass areas and the two sites should be on separate systems.

Good irrigation design, regular maintenance and

proper scheduling can save at least 50% of our water

used for turfgrass irrigation.

Efficient Water Management

Good irrigation design

Proper installation

Regular maintenance

Proper scheduling

Turfgrass use not only determines water requirements, but frequently determines irrigation schedules. On baseball fields and golf courses the use of the site interferes with irrigation scheduling. For example, the use of this baseball facility during spring and summer prevents proper irrigation scheduling. During peak use, the irrigation manager can not apply more than 0.2 inch of water per application. If more water is applied the field would be too wet to play on. Consequently, light, frequent applications of water are required during peak use of the field. Such scheduling results in very shallow rooted turfgrasses.

Reducing water losses during periods of water restrictions requires close monitoring of soil roots zones and irrigation systems.

Irrigation should be scheduled during periods of peak water availability and when evaporation and drift are at a minimum. In urban areas this usually requires irrigation between midnight and 6:00 a.m. However, on large turf areas such as golf courses and commercial landscapes, as much as 10-12

hours are required to complete the irrigation cycle.

Reducing Water Losses

Schedule irrigation to meet grass

needs

Reduce runoff

Reduce leaching

Reduce evaporation and drift

On sloping sites water runoff following irrigation and rainfall accounts for over 50% of the water applied. Frequent aerification on the sloping sites can dramatically reduce water runoff. Also, watering intermittently for short periods over an 8-10 hour period will reduce runoff.

Aerification equipment such as this Aeravator very effectively increases the infiltration rate of the site and reduces water runoff.

Nighttime irrigation when evaporation and drift are at a minimum can save significant amounts of water. This

partially explains the requirement for nighttime watering during periods of

restricted water availability. Repairing irrigation leaks also save significant amounts of water. In urban areas,

irrigation leaks result in as much as 50% loss of water.

Other Irrigation Losses(15 to 50%)

Evaporation

Wind drift offsite

Irrigation leaks

Today, irrigation controllers can be set to water intermittently and can be connected to weather stations through the internet to apply water based on ET losses. Controllers can also be automatically shut off by significant rainfall.

Moisture sensors can also be used to control the application of water. Where such devices are used, irrigation rates are reduced as much as 50%.

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201986 1987 1988 1989

Bermudagrass Fairways - Houston

Inches of water

Rainfall and Irrigation

Irrigation

A case study involving these water saving practices on a Houston area golf course resulted in reducing irrigation rates from 60 inches of water per year to 30 inches and improved the quality and playability of the golf course.