Estimating Turfgrass Water Needs
Estimating Turfgrass Water Needs
Lawns, sports fields, golf courses and other turfgrass plantings closely match the ETo assumptions, which are the grass is:
♦ well-watered with soil moisture unlimited at all times.
♦ growing vigorously.
♦ forming a uniform, nearly continuous canopy that functions as a single big leaf.
♦ grown with the goal of optimum growth and development and yield (mowing is required).
♦ using water in direct proportion to the rate of ETo.
So, true crop coefficients (Kc) have been scientifically determined that represent the water needed by common turfgrass species to perform optimally (Table 1). The annual Kc averages are commonly used for irrigation scheduling, but monthly values generate irrigation schedules that more precisely match turfgrass needs.
Note that turfgrasses require an amount of water that is less than ETo to provide acceptable performance during most of the year. However, the total amount of water needed to be applied is almost always greater than ETo because of inefficiency and non-uniformity of irrigation system performance. Also, note that warm-season turfgrasses (bermudagrass, zoysiagrass, St. Augustinegrass) need significantly less water than cool-season turfgrasses (tall fescue, rye grass, Kentucky bluegrass) during the growing season.
Turfgrass Crop Coefficients (Kc)
We use the turfgrass Kc’s in Table 1 with ET information to determine the approximate amount of water that a lawn or other turfgrass planting will need for optimum performance. Tall fescue and other cool-season grasses will survive with many brown areas but provide cover when irrigated at about 60% of ETo. Bermuda and other warm-season grasses will provide similar minimal performance when irrigated at about 40% of ETo.
Once we decide the level of turfgrass performance that is acceptable, we use this information with the irrigation system precipitation rate and uniformity factors to determine how long to run the irrigation system. The next step is to decide the irrigation frequency, or how often to apply water. A table for water use classification of landscape species has a list of plants and their Eto Table1.