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In central Ohio the past few weeks there has been relatively low relative humidity coupled with sunny and windy conditions. These conditions have been ideal for rapid drying out of turf.

Many factsheets & publications will recommend irrigating turf based on replenishing the evapotranspiration (ET) rate. This is a figure derived from the amount of water lost from the soil surface (evaporation) coupled with water lost from the plant (transpiration). ET rates are usually found on a weather data system purchased by the sports facility or golf club.

ET rates are usually a predicted value calculated from a weather station based on a cool season grass growing in native soil under well-watered conditions. With that in mind, turf managers taking care of native soil fields need to be applying around 1.5 inches water per week just to replenish current ET rates.

SAND-BASED FIELDS

It is more difficult to predict water loss and replenish water on a sand-based field. Sand fields are constructed as such to achieve a water retaining porosity of around 15-25% of the soil volume. This poor water retentivity & the relatively shallow depth of cool-season grasses means that the effective soil depth for retention of useful water is around 5 inches. If the available water capacity is approx. 15% of the 5 inch depth, then the sand may only contain about 3/4 inch of water. Based on the ET rates above, this water reserve would be exhausted in 3 days. If the field was a newly constructed 100% sand field, the available water may be as low as 5 or 10%. This would significantly reduce the water content at a 5 inch depth to 1/4 - 1/2 inch, which would be exhausted in 1-2 days.

While all of this technical information is helpful to the turf manager, there really is no substitute for going outside and physically checking the turf and the soil with a soil probe. As Dr. Danneberger quips "This isn't brain surgery - if the soil is dry, turn on the water"

Posted by Pamela Sherratt