Article : 2008 June LSMP Sports Turf Management: Field Irrigation

Field Irrigation

Irrigating after dew develops or before the morning dew dries off does not increase disease problems. In addition, to reduce soil compaction, irrigation should be performed 24 to 48 hours before major field use.

It is very difficult to maintain an athletic field without proper irrigation. A means to supplement rainfall, irrigation should be scheduled accordingly. The frequency and duration of each watering obviously depends on environmental factors and limitations of the irrigation system.

Ideally, field irrigation needs to be performed prior to turf wilt. Most grasses have a darker or a dull bluish-green color, and the leaf blades begin to fold or roll when the grass is under water stress. Irrigation should begin when these signs are first observed.

When to Irrigate

It is more efficient to irrigate at night rather than during the day because less water is lost to evaporation. Furthermore, it is advisable to irrigate is just prior sunrise. In the early morning hours, there is relatively less wind and lower temperatures, both good factors in getting proper field coverage.

On many fine-textured soils, runoff may begin before the soil is properly wet to the right depth. When runoff occurs, stop irrigating and let the water soak into the soil for one to two hours before starting again. It may be necessary to repeat this cycle several times before irrigation is complete.

Irrigation Audits

It is essential that field managers know the water requirements of turfgrass varieties and the application rates and problem spots of their irrigation systems.

To reinforce the importance of proper irrigation, researchers at Texas A&M conducted irrigation audits around the state to determine application rates and application uniformity on athletic fields. They found that even some of the best designed irrigation systems are just barely adequate in their application uniformity and application rates are all very site specific considering water pressures, pipe sizes, nozzle sizes, etc. Some turf is pretty forgiving with too much or too little water, but proper management that leads to the highest quality and most vigorous turf requires more stringent water management. Water control is also important to environmental issues.

Enough water should be applied to soak the soil to a depth of at least 6 to 8 inches. On medium-textured soils, this usually means applying about 1 inch of water per week during the summer. Light, frequent irrigations encourage shallow, weak root systems and thatch accumulation.

How It’s Done

An irrigation audit involves a visual inspection of all irrigation heads to determine that all function properly, throw in the correct direction, have the correct nozzles, are not clogged, are not impeded by tall grass or a structure, etc. After inspection, set out a series of cups in a grid pattern over the field or a specific zone of irrigation heads. Draw a diagram of the field and label the placement of each individual cup or can. Now turn on the sprinklers for a specified amount of time. After the irrigation is off, measure the amount or depth of water in each cup or can. Match the depth or amount with the proper placement on the diagram and continue. When all cups are collected, find an average amount or depth of water in each cup and use that to determine the application rate per hour.

You will also discover wet or dry spots using this grid pattern. You will also learn much more useful information with the more cups or cans used in the grid pattern. Try to conduct your irrigation audit during a time that you would usually do your irrigation. You don’t want to conduct an irrigation audit during a windy afternoon if you normally irrigate in early morning with very little wind.

Remove soil cores to determine any layering problems and to determine the depth to which was wetted by running the irrigation system for the determined amount of time. The key is to irrigate deeply and infrequently and to a depth of six inches or more. You don’t want to overwater where a large portion of the water moves beyond the roots taking valuable nutrients with it. We have seen considerable leaching of nitrogen and micronutrients due to excessive irrigation.

Sources: Athletic Fields @ Aggieturf; Athletic Field Management by Gil Landry, Georgia Extension Turf Specialist and Tim Murphy, Georgia Extension Weed Science Specialist

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