FROM ROOTS TO SHOOTS
How Dry is My Soil?
P
robably one way to guarantee that we will have a wet summer is to write an article on a tool to better understand rootzone moisture and improve irrigation efficiency. Well, let’s tempt fate. That being said, the 2012 winter was one of the driest on record and the spring so far is following in its footsteps. Most golf courses in Ontario had their irrigation systems up and running 4-6 weeks earlier than usual. Localized dry spots were showing up in mid-March and non-irrigated turf in fairways and roughs was not even growing in April due to a lack of soil moisture. A few watersheds are at Level 1 under the Ontario Low Water Response Plan, which means a voluntary 10 per cent reduction in water taking. All that being said, let’s talk about a tool that will help you use your irrigation system more efficiently, conserve water, and improve playing conditions. I’m referring to a Time Domain Reflectrometry unit (TDR). The probe measures an electrical signal between the volume of soil between two rods and converts it into volumetric water content (VWC). The technology is accurate across a broad
range of soil types, from heavy clay to a sandy loam soil, such as a USGA specification putting green. There are a few different makes and models of portable TDR units available that are easy and quick to use and range from $500- $1,300.
Ground Truthing a TDR Unit The first thing to do when you purchase this new tool is to develop a data base of soil moisture measurements and compare or correlate the information with visual assessments. These assessments are what you currently use to determine your watering schedule. Measurement readings may be taken before and after an irrigation event of a known length of time. It is important to make sure that you include areas prone to localized dry spots and areas that are the last to wilt. Soil moisture will vary greatly based on soil texture and surrounding environment, so an extensive data base for your own course is a must. This exercise will help to determine what your irrigation threshold is. In other words, how low can you let your volumetric water content go before you schedule an irrigation event.
Dr. Ken Carey measures volumetric water content with a TDR probe.
Most experts suggest a range between 15-25 per cent depending on the soil type and the season. Spring is a good time to do the ground truthing because the turf is generally under less stress.
Where and how many measurements? Not only do you need to measure every green, but it is important to have enough measurements per green to get an adequate picture of the soil moisture status of the entire
Rain Bird Integrated Control System ®
Simple and Reliable Below-ground Irrigation Control Milton 1-800-263-4112, King City 1-866-703-5464, Scarborough 1-416-289-3635 www.vandenbussche.com email: info@vandenbussche.com
10 Green is Beautiful • Spring 2012
TM