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Principles of Turfgrass Irrigation

Department of Crop and Soil Sciences - Cooperative Extension

A practical watering program embodies three basic concepts. Each concept may be setforth as a question:

.1 How should water be applied?

.2 How much water should be applied?

.3 How often should water be applied?

While the basic concepts of a good watering program may appear simple, in actualpractice there are many and varied problems associated with the successful applicationof each.

Manner of applying water

Water should never be applied at a rate faster than it can be absorbed by the soil. Theability of a soil to absorb moisture at a given rate depends upon a number of factors,most of which are directly or indirectly associated with certain physical soil problems.Soil properties that govern water infiltration (movement of water into the soil) aretexture, structure, and the degree of compaction. Texture (size of soil particles) andstructure (arrangement of soil particles) influences not only the infiltration of water, butalso water-holding ability and soil drainage.

Likewise, soils that exhibit good aggregation (a measure of structure) permit morerapid infiltration of water than soils that display poor structural properties. Compactionrefers to a condition in which aggregation is reduced or absent; hence, the soil is dense.

The degree of compaction at or near the surface is of special importance insofar asinfiltration of water is concerned. It has been shown experimentally that a very thinlayer of compacted soil will substantially reduce the rate of infiltration.

Another very important factor that influences the ability of a soil to absorb moisture isthe rate at which the water is applied. Sprinklers that do not adequately dispersemoisture, as well as sprinklers that deliver a large volume of water within aconcentrated area, tend to cause surface runoff. Whenever water is applied at a ratefaster than it may be absorbed by a given soil, the water is being wasted.

Amount of water to apply

The amount of water to apply at any one time will depend upon the water-holdingcapacity of the soil, the amount of moisture present when irrigation is started, anddrainage.

The water-holding capacity of the soil will, to a large extent, determine how much waterwill be needed at any one time. Loams and clay loams are generally considered to havedesirable water-holding capacity, whereas sands display very little water-holdingcapacity. A sufficient amount of moisture should be applied to insure that the entire

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root zone will be wetted. Once the soil has been wet throughout the root zone or aftercontact with subsoil moisture has occurred, any additional water applied will merely fillthe large pores and be excess.

Removal of excess water from soils is referred to as drainage. Unless soil are adequatelydrained, many problems arise because of the slow removal of excess water.

Frequency of irrigation

The frequency of irrigation depends on the type of grass, the soils physical properties,and the climatic condition especially rainfall, humidity, temperature, and windmovement.

It is often said that many turfgrass problems may be attributed to improper watering.Perhaps one of the most important factors contributing to improper watering isfrequent irrigation watering too often. In general, it is an excellent idea to let thecondition of the grass determine when to apply moisture. On most general turfgrassareas the time to apply moisture is just as the plants begin to wilt. As a matter of fact,

with one possible exception, this could become a rule of thumb for watering turfgrass.

The exception is on newly seeded areas which must be kept moist during the period theseed is germinating and seedlings are becoming established.

Frequent, shallow watering tends to keep the upper layers of soil near a point ofsaturation most of the time. This encourages shallow rooting and promotes weak turf

which is susceptible to disease and insect attack as well as damage from traffic. Thepractice of watering deeply only when plants show signs of wilting is for most turfgrassareas a practical approach to a sound watering program and it is a big step forward inthe development of healthy, vigorous turfgrass. Far too many of our turf areas are

watered too frequently and for too short a time.

Irrigation Equipment

It is important that the sprinkler used delivers a uniform amount of water over the areacovered by the sprinkler throw. Many commercially available home lawn sprinklers donot give uniform coverage. You can check your sprinkler output by placing a row of onepound coffee cans (or any cans of equal size) in a line at one to two foot intervals fromthe sprinkler to the point of furtherest throw. By allowing the sprinkler to run for aknown time ( to 1 hour) the amount of water in each container can be measured andthese results plotted on graph paper to show the distribution pattern and applicationrate of that particular sprinkler. Normally this procedure should be used at a time otherthan during periods of peak community water use, as water pressure may be lower thannormal during these periods.

Poor water distribution can also be due to human error. Often a stationary sprinkler isallowed to remain on one area of the lawn longer than on another. This can beovercome by using a traveling sprinkler that moves over the area at a uniform pace.

In summary, watering practices should provide for the proper distribution of water,permit good water infiltration, and assure sufficient water retention to support plant

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growth without irrigation for a reasonable time. Above all, good watering practicesshould provide for the removal of excess water. Finally, a sound watering programshould utilize only as much water as is needed by the turfgrass plants to producehealthy, vigorous wear-resistant turf.