DROUGHT RESISTANCE ASPECTS OF TURFGRASSES IN THE SOUTHEAST - EVAPOTRANSPIRATION AND CROP COEFFICIENTS

Water-use data obtained under the climatic and soil conditions typical of the southeastern USA are very Limited. Seven of the most commonly used turfgrasses in the Piedmont region of the humid Southeast were evaluated in a field study under edaphic stresses common to the region for seasonal evapotranspiration (ET) and development of Class A weather pan coefficients (k(p)) and FAO Penman crop coefficients (k) for irrigation scheduling. Time-domain reflectrometry (TDR) was used to determine ET for each turfgrass (i.e., ET(c)) during soil dry-down periods in 1989 and 1990. Estimated ET by the weather pan and Penman methods was used with ET(c) to develop crop coefficients. Grasses were Tifway bermudagrass (Cynodon dactylon X C. transvaalensis), common bermudagrass [C. dactylon (L.) Pers.], Meyer zoysiagrass (Zoysia japonica Steud.), common centipedegrass [Eremochloa ophiuroides (Munro.) Hack.], Raleigh St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and Rebel II and Kentucky-31 tall fescue (Festuca arundinacea Schreb.). Average summer ET rates were common bermudagrass (3.03 mm d(-1)), Tifway bermudagrass (3.11 mm d(-1)), Raleigh St. Augustine (3.28 mm d(-1)), Meyer zoysiagrass (3.54 mm d(-1)), Rebel II tall fescue (3.57 mm d(-1)), Kentucky-31 tall fescue (3.69 mm d(-1)), and common centipedegrass (3.80 mm d(-1)) with the latter two being significantly higher than the bermudagrasses ET rate. Observed ET values were 40 to 60% lower than reported for the same genotype from arid and semi-arid regions under nonlimited soil moisture. Under humid environments, ranking grasses for drought resistance based on relative ET does not correlate well with field observations of drought resistance based on wilt and Leaf firing. Crop coefficients for the same species were generally higher than those reported under less humid conditions. Warm-season species exhibited different coefficients and could not be grouped together for a common coefficient. All grasses had substantial changes in coefficients over the growing season; thereby indicating the need for seasonal adjustments when using these for irrigation scheduling.