Lower DU Can Lead to More Uniform Soil Moisture

The golfing season in northern climates includes managing cool-season turf playing surfaces through stressful summer months (e.g. high temperature, low moisture). To prepare for summer stress, use opportunities in the spring during dry periods to apply strategic moisture stress to your playing surfaces by purposefully withholding water from the plant. Allowing soils to dry and create stress in this way often results in increased rooting and improved drought stress tolerance that will pay off in the summer.

In addition, you should assess your irrigation system’s ability to produce uniform soil moisture before summer stresses occur. The application of supplemental irrigation water to maintain uniform soil moisture is critical for maximum playability and stress tolerance during dry periods. Increased accuracy in applying water through a well-designed in-ground irrigation system also allows for significant water conservation. These concepts are promoted in the following two BMP statements:

  • Design and maintain irrigation systems to uniformly apply water to the intended area of management.
  • Assess system efficiency through regular audits of application rate and uniformity.

However, the application efficiency of an irrigation system, measured as Distribution Uniformity (DU), may not always be the most effective measurement of system application that results in uniform soil moisture. This is especially true for undulating surfaces, with higher elevations often too dry and lower elevations too wet.

Applied water sheds rapidly, internally and externally, in a progressive fashion from higher elevations, and along the surface, down to the lower elevations. Research investigating sloped greens conducted at Michigan State University suggests building variable soil profile depths to address the uniquely inconsistent water holding properties found on sloped terrain when constructing new putting surfaces. This will insure shallower depth of rootzone profiles in the higher elevations that will hold more water and deeper rootzone profiles in the low areas to expedite drainage.

The only option to address the disparity in soil moisture on existing undulating surfaces, when adding drainage is not an option, is to alter the DU. In fact, research from the University of Wisconsin-Madison has demonstrated that irrigating a putting surface with a one percent slope required a change in DU from 80 percent to 17 percent to apply the correct amount of water for uniform soil moisture as measured by a time-domain reflectometer (TDR) probe (Spectrum 300).

Therefore, the BEST irrigation practice includes measuring soil moisture to assess system uniformity—not traditional catch-can tests. This will insure that plants have the moisture they need to provide firm playing conditions.