Water is one of our most valuable natural resources and water conservation continues to be a major national priority [Vickers, 2001; Texas Water Development Board (TWDB), 2007]. As a result of population growth, current potable water supplies will be insufficient by the year 2050 in Texas (TWDB, 2003). Currently, 7.8 billion gallons, or ≈30% of all potable water, is used outdoors (U.S. Geologic Survey, 2006) primarily for landscape irrigation (Kjelgren et al., 2000; Vickers, 2001; White et al., 2004).
Landscape plants provide an aesthetic appeal to urban landscapes, prevent erosion of the soil that impairs surface water supplies, sequester carbon, add oxygen to the atmosphere, and improve recharge of groundwater (Beard and Green, 1994). Irrigated areas within the built landscape can also increase property values. Yet, end-user lack of understanding of best management practices for landscape water management will routinely contribute to excess water use. In a study of 800 home consumers in College Station, TX, it was estimated that more than 24 to 34 million gallons of excess water, that is water in excess of an irrigation coefficient of 1.0 of the yearly reference evapotranspiration, were used annually for landscape irrigation during 2001 through 2003 (White et al., 2004). Appropriate landscape design and planning has been heralded for decades as a step toward water conservation (Welsh et al., 2000), yet water consumer irrigation practices have not changed with landscapes designed for water conservation (Peterson et al., 1999).
Evapotranspiration (ET) is the amount of water lost through evaporation from the soil and plant surface plus that lost through plant transpiration. Reference evapotranspiration (ETo) water loss rate is based on environmental demands for a cool-season turf completely covering the ground. Landscape irrigation based on ETo is an emerging area of water conservation that links plant water use to irrigation water replacement rates and schedules. There is evidence that ETo weather station data can be used in irrigating landscape plants (Shaw and Pittenger, 2004; White et al., 2004), yet there is a lack of information on the fundamental seasonal relationships between ETo and actual evapotranspiration of turfgrasses, native grass species, tree species, and mixed species landscapes under different climates. An understanding of this relationship is critical to providing accurate recommendations for landscape irrigation based on ETo.
A variety of state-of-the-art technologies are available for reducing irrigation water use in amenity landscapes. One of these “smart irrigation” technologies is an ET-based controller. McCready et al. (2009) compared the effectiveness of an ET-based controller technology treatment with a time-based system with 2 d of irrigation per week without any type of sensing mechanism. Compared with the time-based system, the ET-based treatments used 25% to 62% less water without compromising turf quality. This demonstrates the benefit of using ET-based controllers in landscape irrigation, but there is a gap in the knowledge of what fraction (e.g., 0.7, 0.8) of the ETO is needed in the mixed-species landscape. Coupling ET-based plant water use with ET-based irrigation controllers can provide a means of accurately applying water to the landscape.
It is well documented that sodic and saline soil conditions can alter soil water use and transpiration in landscape plant materials (Eom et al., 2007; Munn, 2002; Wang and Nii, 2000). Dean et al. (1996) demonstrated a differential response in bermudagrass and tall fescue growth in arid climates where excess salt and water-induced stress were factors. The Dean et al. study also demonstrated that both grasses could be grown with moderately saline water if irrigation water volume was above a species-specific threshold value. Carrow and Duncan (1998) documented how excess soil sodium (Na) levels can lead to soil structural deterioration and to specific ion toxicity in shoot and root tissue. Sodic soil conditions may develop in amenity landscapes if high Na irrigation water is used. Therefore, the actual ET/ ETO relationship of plants may vary between sodic landscape sites and non-sodic landscape sites. As sources of potable fresh water are depleted, lower-quality water increasingly becomes used for irrigation of turf and woody plants.
The objectives of this study were to 1) compare landscape crop coefficients (KL; actual ET to ETo) by landscape plant treatment; and 2) determine if seasonal differences in KL occur within sites.
Aitkenhead-Peterson, J.A. , Steele, M.K. , Nahar, N. & Santhy, K. 2009 Dissolved organic carbon and nitrogen in urban and rural watersheds of south-central Texas: Lands use and land management influences Biogeochemistry 96 119 129
Barta, R. 2004 Stretching urban water supplies in Colorado: Strategies for landscape water conservation Colorado Water Resources Research Institute, Special Report No. 13
Beard, J.B. & Green, R.L. 1994 The role of turfgrasses in environmental protection and their benefits to humans J. Environ. Qual. 23 452 460
Ben-gal, A. & Shani, U. 2002 Yield, transpiration and growth of tomatoes under combined excess boron and salinity stress Plant Soil 247 211 221
Brown, K.W. , Thomas, J.C. & Aurelius, M.W. 1985 Collecting and testing barrel sized undisturbed soil monoliths Soil Sci. Soc. Amer. J. 49 1067 1068
Brown, P.W. , Mancino, C.F. , Young, M.H. , Thompson, T.L. , Wierenga, P.J. & Kopec, D.M. 2001 Penman Monteith crop coefficients for use with desert turf systems Crop Sci. 41 1197 1206
Carrow, R. 1995 Drought resistance aspects of turfgrasses in the southeast: Evapotranspiration and crop coefficients Crop Sci. 35 1685 1690
Dean, D.E. , Devitt, D.A. , Verchick, L.S. & Morris, R.L. 1996 Turfgrass quality, growth, and water use influenced by salinity and water stress Agron. J. 88 844 849
Eom, S.H. , Setter, T.L. , DiTommaso, A. & Weston, L.A. 2007 Differential growth response to salt stress among selected ornamentals J. Plant Nutr. 30 1109 1126
Ervin, E.H. & Koski, A.J. 1998 Drought avoidance aspects and crop coefficients of kentucky bluegrass and tall fescue in the semiarid west Crop Sci. 38 788 795
FAO Irrigation and Drainage Papers-56 1998 The Food and Agriculture Organization web site 27 Feb. 2009 <http://www.fao.org/docrep/X0490E/x0490e06.htm>.
Kim, K. & Beard, J. 1988 Comparative turfgrass evapotranspiration rates and associated plant morphological characteristics Crop Sci. 28 328 331
Levitt, D.G. , Simpson, J.R. & Tipton, J.L. 1995 Water use of two landscape tree species in Tucson, Arizona J. Amer. Soc. Hort. Sci. 120 409 416
Maupin, C. & Struve, D.K. 1997 Red oak transplanted to different bulk density soils have similar water use characteristics J. Arboriculture 23 233 237
McCready, M.S. , Miller, G.L. & Dukes, M.D. 2009 Water conservation potential of smart irrigation controllers on St. Augustinegrass Agr. Water Manage. 96 1623 1632
Mehlich, A. 1978 New extractant for soil test evaluation of phosphorus, potassium, magnesium, calcium, sodium, manganese, and zinc Commun. Soil Sci. Plant Anal. 9 477 492
Peterson, K.A. , McDowell, L.B. & Martin, C.A. 1999 Plant life form frequency, diversity, and irrigation application in urban residential landscapes HortScience 34 491
Sagi, M. , Dovrat, A. , Kipnis, T. & Lips, H. 1998 Nitrate reductase, phosphoenolpyruvate carboxylase, and glutamine synthetase in annual ryegrass as affected by salinity and nitrogen J. Plant Nutr. 21 707 723
Saha, S. , Trenholm, L.E. & Unruh, J.B. 2007 Effect of fertilizer source on nitrate leaching and St. Augustinegrass turfgrass quality HortScience 42 1478
Shaw, D.A. & Pitttenger, D.R. 2004 Performance of landscape ornamentals given irrigation treatments based on reference evapotranspiration Acta Hort. 664 607 614
Texas Water Development Board 2003 2003 Water use survey summary estimates TWDB Austin, TX 5 Oct. 2009 <http://www.twdb.state.tx.us/data/popwaterdemand/2003Projections/HistoricalWaterUse.asp>.
Texas Water Development Board 2007 2007 State water plan TWDB Austin, TX 5 Oct. 2009 <http://rio.twdb.state.tx.us/publications/reports/State_Water_Plan/2007/2007StateWaterPlan/Chapter04.pdf>.
Wang, Y. & Nii, N. 2000 Changes in chlorophyll, ribulose bisphosphate carboxylase-oxygenase, glycine betaine content, photosynthesis and transpiration in Amaranthus tricolor leaves during salt stress J. Hort. Sci. Biotechnol. 75 623 627
Welsh, D. , Welch, W. & Duble, R. 2000 Landscape water conservation Texas A&M University 5 Oct. 2009 <http://aggie-horticulture.tamu.edu/extension/xeriscape/xeriscape.html>.
White, R. , Havlak, R. , Nations, J. , Pannkuk, T. , Thomas, J. , Chalmers, D. & Dewey, D. 2004 How much water is ‘enough’? Using PET to develop water budgets for residential landscapes TX Water Resources Institute TR-271 College Station, TX