Unusual Turf Problems

Gathering more data, then taking the time to understand what it’s telling you about your greens can eliminate the risks of over-watering.

Too often the response to a hot, dry day is to fire up the irrigation at night, along with the water budget. This reaction is based on a perceived need, with no real basis in actual soil moisture levels or daily losses.

Historically, the watering requirement has largely been determined by visual clues – either looking at the turf, or sampling and guessing at moisture levels. Yet research shows that visual clues alone tend to overestimate the need for water. Until recently, suitable moisture meters were not available or affordable. That’s now changed and Turf Managers can quickly and accurately assess soil moisture, then make informed decisions on whether to irrigate and how much to apply.

Get to know your equipment

Soil moisture meters are simple tools that provide immediate results. Generally two probes are fully inserted into the soil to provide a numerical assessment of moisture levels. Depending on the meter used, the length of probes should be similar to the actual root depth. A reading is an average of the measurements along the length of the probes, so the surface could be much drier or wetter than at the probe tips. So it is important that the probe is pushed fully into the soil. Most meters come with digital readouts and some can log both your location and the moisture level. A range of readings from across the site will help evaluate the variation in the turf. These devices do have their limitations; different meters can give different readings for the same site, and some meters are influenced by the salinity of the soil. The key is to build a body of information through regular data collection using the same meter. In that way, you can more confidently gauge the actual moisture content, the changes each day and the impact of irrigation.

Examples of various hand-held moisture meters (above) and a collapsible frame (below) to save bending over. This model can also have a GPS unit fitted.

Get to know your site

Irrigation management should aim to apply the least amount of water necessary to support plant health and provide a quality-playing surface. The target moisture level needs to be benchmarked for the individual venue, or areas within the venue, and account for differing soil types, climatic conditions and grass species. When the aim is to get an average reading over a green, it is common to divide the green into ‘grids’ and record the moisture level in each one. Often the green is divided into 9 (3 grids in the front third, 3 in the middle and 3 in the back third). These are averaged to allow comparisons between different greens on the course. They can also identify ‘drier areas’ that can be hand-watered, thereby avoiding the need to irrigate the entire green.

Dividing the green into grids assists in quantifying differences and localising irrigation requirements.

Setting target moisture ranges

In conjunction with a visual assessment of the surface, sample a range of wet and dry areas (by probe and soil sampling) to get a feel for the upper and lower limits of the ideal moisture range i.e. where turf is healthy and surface conditions are desirable. A wide range will be likely. Generally
turf is quite happy at approximately 16-20% Volumetric Moisture Content, but maintaining this level does not offer much flexibility should there be an irrigation failure; just as setting the upper limit too high doesn’t leave any capacity for an unexpected downpour or sustained wet period. So a range of 20-25% is a good place to start. This process will also help to calibrate your eye and get ‘a feel’ for the actual soil moisture content.

Sampling reveals differences that are not apparent by looking at the surface alone.

Making informed decisions

Now that you have established a target moisture range, the next step is to understand how evapotranspiration (eT), rainfall and irrigation run-times impact on soil moisture at your location. This will let you refine your target ranges and irrigation practices with more confidence.

ET rate

Sample an area first thing in the morning and again in the evening, through a range of weather conditions. This will provide good information on daily moisture losses for various climatic conditions and help you relate eT data for your region with actual soil moisture loss on your site. ET data is available online and for some regions will be listed in the local paper. Actual soil moisture loss within the root zone is typically ½ – ⅔ of reported eT i.e. Newspaper eT 5mm = Turf eT 2.5-3mm.

Irrigation applications

Sample late afternoon, prior to the normal irrigation cycle and sample again the following morning (after an irrigation cycle). This will indicate how irrigation changes the soil moisture, which can then be related back to the application rate. Sampling the top and bottom of sloped areas will also highlight any infiltration issues due to run-off. To minimise run-off, match the application rate with infiltration e.g. increase aeration (mini-tyne) and/or employ multiple short run-times to reduce run-off and apply a uniform amount of water to sloped areas.

Impact of rainfall

Sample before and after a measured (by rain gauge) amount of rainfall i.e. X amount of rainfall = X amount of increase to soil moisture.

Achieving the best outcome

Avoid the “do it once and she’ll be right” approach. Instead adopt a sustained approach to recording moisture levels throughout the year. The more data collected, the more precise your decision-making becomes with regard to watering. Knee jerk reactions leading to over-watering on hot days can be prevented. Irrigation scheduling can be set with more confidence.

Example of drier areas within a green.

Written by Agronomists at New Zealand Sports Turf Institute