University of Florida

ETc Rates of Warm-Season Grasses
Commonly Used in Florida

Summaries of research carried out in Florida are presented based on direct measurement of evapotranspiration. The highest ETc rates shown by some of the results were typically associated with well-watered conditions. This information is summarized in Table 2.

A relatively new method to estimate crop evapotranspiration was used by Jia et al. (2009). Crop evapotranspiration (ETc) rates were estimated for bahiagrass under well-watered conditions using the eddy correlation method. This method overcomes the need to determine each component in the water balance by using the energy balance approach (Tanner and Greene, 1989). The results of this study showed that the highest average monthly ETc rate (4.2 mm d-1) occurred in May. The lowest average monthly ET rate (0.7 mm d-1) occurred in January. Table 2 shows more detailed information about ETc for bahiagrass.

Stewart et al. (1969) studied ETc rate as a function of plant density and water table depth in South Florida using Tifway bermudagrass growing in non-weighing evapotranspirometers (12 waterproof rectangular concrete tanks, 150 cm depth and having a plot area of approximately 4.1 m2). Depth to water table was 30, 60, and 90 cm. Water replacement ranged from well watered conditions at 30 cm water table to partial stress at a 90 cm water table depth. The plant cover treatments were established by killing part of the sod to give the preselected 0-, 1/3-, 2/3-, and full-sod cover treatments. An annual water balance data showed a linear decrease between degree of plant cover and annual ETc rate with 30, 60, and 90 cm. ETc rates increased with sod cover at water-table depths of 60 cm (from 1,059 mm y-1 (2.9 mm d-1)-full sod- to 396 mm y-1(1.1 mm d-1) -no sod-), and 90 cm (from 889 mm y-1 (2.4 mm d-1) -full sod- to 488 mm y-1(1.3 mm d-1) -no sod-). ETc rates decreased with cover for the water table depth of 30 cm (from 1,064 mm y-1(2.9 mm d-1) -full sod- to 1,176 m m y-1(3.32 mm d-1) -no sod. Evaporation from bare soil (no sod, 1,176 mm y-1 (3.2 mm d-1)), with a 30 cm water table was about 11% more than from full sod cover (1,064 mm y-1 (2.9 mm d-1)) in 1967. The ground surface of this treatment was moist continuously, indicating that the capillary fringe reached the soil surface.

A similar experiment but testing different treatments are shown in Stewart and Mills (1967). St. Augustinegrass and Tifway bermudagrass growing in non-weighing evapotranspirometers at Ft. Lauderdale, FL, as described at the previous paragraph. The objective of this study was to determine the relation of these turfgrasses water use to different depth to water table (30, 60, and 90 cm), seasonal climate, and plant density. The results showed that evapotranspiration with a 36-in depth to water table was significantly lower than ET with the other two water-table (Table 2) under full cover condition. Results showing the relation between ETc and plant density is described in the previous paragraph.

Some recommendations of irrigation for lawns and gardens in Florida were presented by Haman et al. (1989). They pointed out that irrigation requirements depended on the availability of water, soil moisture, allowable depletion, and evapotranspiration. Monthly values of potential evapotranspiration (ETp) for north and south Florida are shown in their publication. The authors recommended potential evapotranspiration values can be used as turf actual evapotranspiration because their values are approximate. For north Florida, the minimum and maximum ETp was 1.47 mm (December) and 4.83 mm (May/June), respectively. For south Florida, the range went from 2.29 mm (December/January) to 5.08 mm (May). No method for ETp determination was specified.

Table 2: Summary table showing turfgrass species mean daily evapotranspiration (ETc), methodology used to determine ETc, and respective references.

Turfgrass
Species
 ETc rate (mm d-1)
 Study period length
 Methodology
 Reference
Bahiagrass
 Jan (0.73)
Feb (0.87)
Mar (1.92)
Apr (3.62)
May (4.22)
Jun (3.31)
Jul (3.13)
Aug (2.85)
Sep (2.51)
Oct (1.87)
Nov (1.44)
Dec (0.81)
 July 2003 through
December 2006
 Eddy correlation
method.
 Jia et al.,2007
Central Florida,
FL.
Tifway bermudagrass

2.90
2.43
2.91


2.33
2.16
3.07


1.81
1.89
3.16
 Full sod treatment:
1965
1966
1967
2/3 sod treatment:
1965
1966
1967
1/3 sod treatment:
1965
1966
1967
 Non-weighing evapo-
transpirometers.
 Stewart et al.,
1969.
Ft. Lauderdale,
FL.
St. Augustinegrass and
Tifway bermudagrass




Jan (1.74)
Feb(2.38)
Mar (2.92)
Apr (3.77)
May (4.25)
Jun (3.61)
Jul (3.90)
Aug (3.85)
Sep (3.27)
Oct (2.90)
Nov (2.20)
Dec (1.62)

Jan (1.62)
Feb (2.27)
Mar (2.77)
Apr (3.57)
May (4.27)
Jun (3.58)
Jul (3.97)
Aug (3.91)
Sep (3.22)
Oct (2.79)
Nov (2.09)
Dec (1.60)

Jan (1.59)
Feb (2.17)
Mar (2.55)
Apr (3.34)
May (4.28)
Jun (3.61)
Jul (3.95)
Aug (4.00)
Sep (3.29)
Oct (2.70)
Nov (2.05)
Dec (1.50)
 5-ty study (1963-67)
Depth to water table:

12 in depth












24 in depth












36 in depth
 Non-weighing evapo-
transpirometers.		 Stewart et al.,
1967.
Ft. Lauderdale,
FL.

 



Southwest Florida Water Management District