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32 GOLF COURSE MANAGEMENT 09.14 Seduced by metric units Growing up and frst working in the turf- grass industry in the United States, I naturally used U.S. customary units ( http://en.wiki pedia.org/wiki/United_States_customary_ units ): inches and feet, pounds and ounces, fuid ounces and gallons and so on. I started to use metric units ( http://en.wikipedia.org/wiki/ Metric_system ) when I went to work as a golf course superintendent in China and Japan, and I have been using these units ever since. I like to use 1 square meter (1 m 2 ) as the base unit. There are a few reasons for this. First, I can see 1 square meter, I can imagine it, and I can think of how that base unit will be man - aged. Then it is simply a matter of consider- ing how many of those base units of 1 square meter are to be managed. Second, the numbers work out in a convenient way in three-dimen - sional space. I'll elaborate on the convenience of this below. Third, I like to work with numbers from 1 to 100, as much as possible, and work - ing with 1 square meter as the base unit is con- venient in this way. Nitrogen might be applied at about 3 grams per square meter per month; in Thailand, one might apply 30 to 50 grams of nitrogen per square meter in a year. Wet - ting agents will be applied at about 2 milliliters per square meter. Spray volumes will usually be from 40 to 80 milliliters per square meter. These numbers fall in a range that is easy to work with, and easy to think about. There are no 100s, no 1,000s, no 10,000s, and few num - bers less than 1. Micah Woods, Ph.D. firstname.lastname@example.org Now for the three-dimensional space of the root zone. For managed turfgrass, the root sys - tem, averaged over the course of a year, can be considered 10 centimeters deep. This is where most of the nutrients will be taken up, where the grass will obtain water, where coring and cultivation practices will be done. Maybe you would like to use a root-zone depth of 7.5 cen - timeters, or 15 centimeters, or 30 centimeters. That's fne, and can be done, but using 10 cen - timeters has some attractive properties. One square meter to a depth of 10 centimeters has a volume of 100 liters. If the volumetric water content (VWC) of the soil is 18 percent, that means there are 18 liters of water in 1 square meter to a 10-centimeter depth. Want to in - crease the soil moisture to 22 percent? That will require 4 liters per square meter. This is also convenient in two-dimen - sional space. One liter of water spread over 1 square meter has a depth of 1 millimeter. If it rains 6 millimeters, that is 6 liters of water per square meter. And if the soil VWC drops from 20 percent to 16 percent from morning to evening, that is a water loss of 4 liters, equiv - alent to 4 millimeters at the surface. That's the evapotranspiration (ET). Not some estimate from a computer, but the real consumptive Presented in Partnership with Barenbrug (turf) One liter of water is 1 millimeter in depth across 1 square meter and will increase soil moisture in the top 10 centimeters of 1 square meter by 1 percent. The golf course is Salobre Golf Resort, Maspalomas, Grand Canary, Canary Islands. Photo by M. Woods water use. Want to compare the ET of a full-sun area to the ET of a shaded area? Measure the dif - ference in VWC from morning to evening at both sites. Now you've got the answer. Thinking of water application in millime - ters and liters translates directly to the VWC in the soil if one assumes the root zone has a depth of 10 centimeters. Of course, a soil moisture meter may have rods at a 6- or 7.5- or 12-centi - meter depth; one can make appropriate adjust- ments in assumptions and estimates. Being able to make important calculations on the fy without much effort makes it easy to start a relationship with the metric system, but be careful. Once you see how easy this is, you may start to use the metric system for fertilizer, topdressing and spray applications, too. Micah Woods is chief scientist at the Asian Turfgrass Cen- ter and an assistant adjunct professor at the University of Tennessee-Knoxville.