Sports Turf Moisture Measurement

I was recently told of a golf club in Eastern England which started to add fertiliser to its golf greens in the 1960s and had fabulous greens. The greenkeeper at a nearby course was told to do the same but unfortunately his grass died and he lost his job.

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The name of the club is irrelevant, but it illustrates the point that managing the needs of the turf can improve the aesthetic and performance of a green, but what works on one location may not work on another - all greens are individual and there is potentially a lot at stake.

One of the most important physical properties to manage is water content. This is one factor which may affect performance in terms of ball roll and bounce but it also effects grass growth, the ability of nutrients to move to the roots, organic matter break down and build up within the soil or as a thatch, fauna and flora populations within the root zone, including pathogen populations and of course trafficking of the green by grounds staff and club members. Soil water therefore has a critical role to play in turf health and our enjoyment of individual greens and the aesthetic of the fairway vista.

Indeed, the ability to monitor soil moisture across a green tells you more than just the variability of moisture, but can highlight drainage issues, the evenness of irrigation, potential turf stress onset or hydrophobicity development. Even the force required to insert the sensor gives you an immediate feel for green conditions. In addition, the presentation of actual figures to a green committee is more powerful evidence for investment than just an opinion. Of course the sensors themselves allow for continuity in determination of water content if one of the grounds team is away. You are not reliant on one individual.

The accurate and reliable measurement of soil water is therefore an important management tool. One could easily say its good basic practice to measure moisture content and no groundsman in today's age should be without a dependable means of assessing water content/status when it is so easy to do.

It is very important to appreciate that soil water content readings from any sensor do not mean all this water is available to the turf. Whilst coarser textured soils may be freely draining and require more irrigation to meet turf demands, clay soils may show high readings but possibly only a small percentage of this is available for plants. This is because clay soils tend to hold onto water in small voids, and roots are not able to generate the suction required to draw it out. Hence a reading of 29% volumetric water content means, from a management perspective, something different in a sand or clay based green. This is an important consideration in natural greens, but is less important in man-made greens where the textural characteristics of the 'soil' should have been carefully selected in the first place to match the drainage characteristics required.

Construction type	Golf green ranges (%)	Pitch ranges (%)
Soil based	15 - 30	20 - 40
Sand based	15 - 25	22 - 32
Links	10 - 20	N/A

When using any hand-held sensor, ground staff can either do spot checks at specific points of concern or interest, or undertake multiple readings in a grid pattern (above). Sports Turf Research Institute (STRI) advocate 9 readings in a 3 x 3 grid. This is straightforward and manageable and gives more information than a single measurement. As any single reading is a volumetric moisture content at a specific point in space and time, it is important to undertake multiple surveys over time to put any one reading into context. Taking readings before and after irrigation - during drain down, before and after fertilisation, frosty, cold mornings or during the heat of a summer day can all give different readings. In this way a green's 'normal' range and variability is characterised and changes due to perhaps disease, uneven irrigations or developing hydrophobicity, or other potential problems can be identified before they develop too far. The early identification of problems can only save remediation costs and time.

A recent collaboration with the STRI has produced a short pictorially dominated guide for using a soil moisture sensor. This guide should have wide audience interest as it briefly details the advantages of moisture measurement to the groundsman in general, how to use the probe and some typical target values.

Using an ML3 ThetaKit proved a revelation for one groundsman. "After 32 years of greenkeeping I thought I had a handle on the moisture requirements of my surfaces….Like many greenkeepers, I relied on a combination of experience and on site weather data to determine irrigation requirements…..but when I started to measure soil moisture content (using an ML3 ThetaKit) and compared the figures against inputs…. I found I was over irrigating when experience was telling me I was spot on." The greenkeeper continued "using this technology has enable me to apply less water, more frequently, leading to potential savings with a drier root zone." Simply put, the use of technology as a management tool allowed him to make better agronomic decisions and save money.

There may not be a single perfect sensor on the market that caters for all sports turf needs but surely the leading levels of accuracy, robustness, durability and ease of use make the ML3 ThetaKit a serious contender for consideration in any purchase.

Author: Dr John Newstead, Delta-T Devices Ltd