Water is critical in maintaining healthy turfgrass. The water budget for an athletic field is like a bank account with deposits and withdrawals. The soil is the bank. Deposits are made by rain (in some places, melting snow) and by watering or irrigation. Withdrawals are made by the grass itself, which uses water, and by evaporation. We need to know about the water budget, not just in general, but specifically for each location because conditions vary significantly.
Watching the weather
Weather conditions control the natural water budget of an area. Besides providing soil moisture via precipitation, evaporation is influenced by temperature, relative humidity, wind and sunlight. Higher temperatures, lower relative humidity, more wind and radiant heating from sunlight all increase water loss.
On a hot, dry summer day, 0.25 to 0.33 inches of water can evaporate from the surface. Most turfgrasses require 1 inch or more of water a week during warm to hot weather. And preferably, this water comes as a long soaking, which allows the water to penetrate deep into the soil, promoting long and healthy roots. Less than this and weakened blades are certainly prone to more damage from heavy use, and the grass may even go dormant. In addition, shallow root systems may develop, which makes the turf more prone to problems.
In an ideal situation, all of a plant’s water needs are met by natural rainfall. This would require not only the proper amount of water but also that the rain would fall at regular intervals and at reasonable rates. Unfortunately, Mother Nature almost never provides this type of consistent rainfall. Even in climates that are relatively wet, precipitation is almost never uniform in amount or occurrence. Typically, watering or irrigation is necessary for healthy turf. Again, a good soaking once or twice a week is preferable.
A rain gauge can be a valuable tool in water management. A single gauge can tell you how much rain has fallen over a field. Multiple gauges can be used to determine the amount of water being applied to various parts of a field during watering. Simple, plastic rain gauges are relatively accurate and inexpensive. There are also soil probes or moisture sensors to determine depth of soil moisture.
There are the two extremes in rainfall that also must be dealt with. A lack of rain over extended periods of time, i.e. drought, certainly stresses turf and all plants. In some regions, drought is a seasonal occurrence.
In the West, summers are dry; drier the further south you head. In southern Florida, winters are dry. These dry spells are to be expected and can be allowed for. Irregular occurring droughts are also typical of all regions. The horrific wildfire that devastated Gatlinburg, Tennessee, last November was preceded by three months of virtually no rain. Usually, 10 inches would have fallen, distributed fairly evenly over those 90-plus days. A great resource for keeping track of drought conditions is the U.S. Drought Monitor. You can check past and current conditions and even see the forecast for the next three months.
Of course, the other extreme is too much water, too quickly. This is particularly a problem with actual sporting events. Baseball and softball infields can become unplayable quickly. Stoppages in play and even cancellations occur frequently.
Other sports, such as football and soccer, can continue during rainfall, but damage to the playing surface can occur if too much water accumulates. Standard practices for good field drainage are readily accessible.
To come up with a good plan to manage an athletic field, you need to know how much rain you can expect. A look at rainfall records is in order. To get an idea of what you can expect at your location, you can check the climate records. Go to the Center for Weather and Climate and find the closet reporting station.
You can check on the normal precipitation or average precipitation your location gets. But again, keep in mind that these are averages taken over a number of years.
An “average” day may be listed as getting 0.1 inches of rain. That almost never happens. For most locations, rainfall occurs on less than half the days, much less typically. In reality, it can rain every day for short stretches or go without measurable rain for weeks.
It pays to check the actual daily recorded weather for a site to see what you will have to deal with.
Additionally, you can go to the National Weather Service and get the latest forecast. If precipitation is expected in the next 48 hours, the forecast will give you the expected starting and ending times, the likelihood of precipitation occurrence given as a percentage and the predicted amounts. The extended forecast out to seven days will also give you the probability of rain by 12-hour periods, but not amounts. This will help you plan your watering/irrigation schedule.
The NWS also has a Quantitative Precipitation Forecast (QPF) for the lower 48 states out to seven days . Keep in mind that forecasting precipitation amounts is very difficult, and the given forecasts may have considerable errors.
For the short range (a few hours out), radar can be used to estimate rainfall rates and total rainfall occurrence. The colors you see on a weather radar display represent rainfall intensities:
Blue is light mist at the most;Green is light rain, about 0.05 inches per hour;Yellow shows moderate rain at a rate of about 0.5 inches per hour;Red, which is usually associated with heavy thunderstorm rains, is at least 2 inches per hour.
Rainfall measurements and forecasts are routine, but information on ET is difficult to come by. There are some sites that record daily evaporation from an open water surface, referred to as an evaporation pan. This gives you some idea of water loss. Actual ET from plants is almost impossible to measure. There is one method, called the Penman-Monteith equation, which provides estimates of ET (called Potential ET or PET) using a variety of measured weather parameters.
Those in the Northeast can go to the Cornell University Turfgrass Program weather page and get this information even in forecasts. For other locales, check your local ag extension service or ag school.