SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
Issue link: http://read.dmtmag.com/i/369217
20 SportsTurf | September 2014 www.sportsturfonline.com Field Science | By Dr. Barry Stewart R ecently I returned to the home farm near Cameron, WI where I grew up. We were going to move the last things out of our farmhouse so it could be sold. In amongst the books in the attic was a small thin book called Arithmetic in Agriculture that must have belonged to my father when he as a student in Dairy Science at UW-Madison in the 50's. On the third page of the book, which was copyright 1951, was a picture of a young farmer in bib overalls sitting at a desk with pencil and notebook. The caption read, "Arithmetic will help you solve many farm problems." Think of this for a minute; the problems in this book were meant to be worked out without a calculator, or a smartphone, or calling a friend who is good at math. A slide rule might be helpful; raise your hand if you can work a slide rule! What a great time we live in, because all these tools are avail- able to use today, although phone a friend is a last resort. A firm grasp of mathematics is also vital for a turfgrass manager. If you make a math mistake you will waste time and money and eventually kill grass. Mathematics allows us to calculate how much of an input to apply, calculate the cost of different applications and determine how many workers or man hours to allow for a project. It is never a bad idea to review and sharpen our mathematical skills and this article is intended to do that. Let's review some principles before we do some calculations. Significant figuReS and pReciSion How accurate do our calculations have to be? It depends on the situation. If we apply a 2x rate of sand topdressing to a field we will not even notice, but a 2x rate of metribuzin and we may be looking at some dead turf. In general, we match the preci- sion of measuring the material to the amount that is going to be applied. We handle sand topdressing with tractor scoops and topdressers and in most cases two significant figures are all that are needed. A typical π inch topdressing application applies 33 yd 3 tons per acre. The 33 represents two significant figures. An application of ammonium nitrate (34-0-0) equivalent to 1 lb N/1000 ft 2 to the playing surface of a football field would require 169.4 lbs. Do we need this kind of accuracy? Four sig- nificant figures? No, in this case we can still use two significant figures and round this number up to 170 lbs. What if we are making an application of MSM Turf to control wild garlic on the same football field? Using the 0.5 oz per 1000 ft 2 rate this application would take 28.8 oz of product and in this instance we can again use two significant figures and round this number to 29 oz. In the case of smaller areas or products with very small use rates three significant figures may be warranted. a poweRful tool One of the most useful and powerful tools that is com- monly used on turfgrass math is the equation of ratios. In many cases we have determined or been given the rate we need for a set area such as 5 oz of product/1000 ft 2 or 2 lbs of product per acre. We know the area over which we will be applying our product and now we must determine how much of the product to apply. For example, the label on kwiksorb wetting agent says to apply 5 fl oz of product per 1000 ft 2 or 218 fl oz/acre. We want to apply this to the playing surface of our sand-based football field that measures 360 ft x 160 ft or 57,600 ft 2 . To solve this we set up the following: In this case our units also align so we do not have to do any conversions at this point. To solve the problem we cross multiply and divide. We could also use the rate for an acre (43,560 ft 2 ) which is 218 fl oz In equal ratios the product of the means is equal to the product of the extremes. What does this mean? Let's write the equation a little different. 218 fl oz/43,560 = 288 fl oz/57,600 TurFgraSS managemenT maThemaTicS 5 fl oz x fl oz 1000 ft 2 57,600 ft 2 = 5 fl oz x 57,600 ft 2 1000 ft 2 = 288 oz of kwicksorb 218 fl oz x 57,600 ft 2 43,460 ft 2 = 288 oz of kwicksorb