   Summer Turf Irrigation - June 17, 1998 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Given the controversial water issues in Yavapai County, it is definitely time to start paying more attention to water conservation in our landscapes. Even if we use natives or other low water use plants, many of us still crave an attractive green lawn. In fact, some researchers say that our desire for a lawn is genetic and stems from a need to avoid predators and forage in a savannah-like landscape. Whatever our reasons for having turf, we need to closely monitor the amount of irrigation water we apply, especially during summer. Studies have consistently shown that most homeowners apply at least twice as much water as their lawns actually need. When summer temperature climbs, so does plant water consumption. The technical term describing plant water use is transpiration. Water is also lost through evaporation from the soil and water on the leaf surfaces. Evapotranspiration or ET describes the water used by both processes. Maybe you've seen the high-tech weather stations on golf courses. These stations predict ET and compute irrigation water needed to replace water consumed the previous day. This approach can also be used in the home landscape if you know three things: species of grass, daily high temperature and sprinkler output. Determining grass species may be difficult for some people, but the following are some general guidelines. If it is fine-bladed and green all year long it is probably perennial rye, Kentucky bluegrass, fine leaf fescue or a mix of all three. Tall fescue is wide-bladed and green all year long. Bermuda grass is dormant (not green) in the winter, grows in the summer and spreads rapidly. In reality, many yards have a mix of all three with others as well. The daily high temperature can be taken from the previous day's paper or an accurate thermometer placed outdoors in the shade four to five feet above the ground. A max/min thermometer will hold the daily high for reading the following morning and is an excellent addition to any gardener's information base. To measure sprinkler output you will need several wide, shallow tin cans (cat food/tuna fish type). Ideally, they should be the same size and the more cans the better. Place the cans at random locations on your lawn making sure that they are all in a zone covered by that particular valve or sprinkler. Run the system for exactly fifteen minutes. Collect the cans and precisely measure and record the depth of water in each can with a ruler. Average the depths. To obtain inches per hour, multiple the average times four. This procedure is called an irrigation audit and will also tell you how well your sprinkler system is functioning. David Kopec, University of Arizona Turf Specialist, has developed a simple system to calculate daily water use based on the previous day's high temperature. For perennial rye, Kentucky bluegrass or fine leaf fescue, apply 0.23" at 70oF, 0.27" at 80oF, 0.30" at 90oF, and 0.34" at 100oF. For tall fescue, apply 0.21" at 70oF, 0.26" at 80oF, 0.31" at 90oF, and 0.36" at 100oF. For Bermuda grass, apply 0.15" at 70oF, 0.19" at 80oF, 0.23" at 90oF, and 0.27" at 100oF. These are simple linear relationships so adjustments are easy to do. For example, tall fescue water use increases by 0.05" for each increase of 10oF. If the previous day's high was 106oF, then you would need to apply 0.39" of irrigation water the following day. From the irrigation audit, you know the inches of irrigation water applied in each zone per hour. This allows you to estimate the irrigation schedule for each zone. Early morning watering is best to minimize evaporative losses and disease problems. If these calculations and measurements are straining your brain, fear not. Anyone that tells you they can apply exactly 0.39" of irrigation water evenly over a large area of turf is telling you a tall tale anyway. These numbers are merely guidelines that estimate turf water consumption. So why bother? Knowing your grass species will help you manage your turf irrigation rates as well as everything else from pests to fertilization. Paying attention to daily temperatures helps estimate water use and potential water conservation. An irrigation audit will show you the weaknesses in your sprinkler system and suggest possible improvements. This adds up to wiser water use, healthier turf and less work in the end. For more information on turf water consumption, irrigation audits, or for answers to your gardening questions, contact Yavapai County Cooperative Extension at 646-9113, or e-mail mgardener@kachina.net. |