Amenity landscape water use continues to be a focus of conservation efforts across the United States (U.S. Environmental Protection Agency, 2014). Water purveyors and municipalities struggle with water salinity, population increases, and drought, which place considerable strain on water supplies (Metropolitan Water District of Southern California, 2014; Niemczynowicz, 1999; Toze, 2006). As fresh water becomes increasingly scarce in terms of meeting demand for it, methods of reducing demand for water will take an increasing precedence in municipal water management (Moss et al., 2013). Landscape water conservation methods and techniques using new technology or science-based principles will continue to contribute to managing water resources (Cabrera et al., 2013).
The benefits of having landscape plants in the built environment include noise reduction, erosion prevention, shade, increased property value, and aesthetic benefits (Frank, 2003). Turfgrasses have been shown to improve percolation of rainfall, urban heat dissipation, and reduced fire hazard to structures (Beard and Green, 1994). Irrigation water needed in landscapes to supplement non-sufficient precipitation during the growing season is a well-documented and a substantial portion of municipal water use (Cabrera et al., 2013; Romero and Dukes, 2011; Runfola et al., 2013). A study by Mayer et al. (1999) found average outdoor water use across 12 geographically diverse American cities was 58% of total residential consumption. In central Florida, Haley et al. (2007) found 64% of residential water use was outdoors. That study was based upon 27 cooperating residential homes over a 30-month period. The City of Phoenix estimates 45% of its potable water delivered to residents is used outdoors (City of Phoenix, 2011). Hermitte and Mace (2012) documented indoor and outdoor residential water use for 259 Texas cities from 2004 through 2008. Their study determined on average 31% of residential water usage was outdoors.
The quantity of water used to irrigate a landscape may be influenced by several very broad factors. Spinti et al. (2004) found the amount of time a resident had spent in a desert climate influenced landscape irrigation habits. Those residents spending a shorter period of time in a desert were more likely to conserve water in their landscape. Use of an automatic sprinkler system in a landscape may have an impact on water quantity applied (Mayer et al., 1999). Mayer et al. (1999) and Runfola et al. (2013) determined total lawn area was a significant predictor of annual landscape water use providing a positive correlation. Landscapes in climates with higher average temperatures tend to use more irrigation water than landscapes with moderate temperatures (Breyer et al., 2012; Mayer et al., 1999). Landscape water use also tends to increase during warmer months of the year (Breyer et al., 2012; Kjelgren et al., 2000).
Landscape water conservation methods and techniques continue to gain acceptance in the United States. The Irvine Ranch Water District (Irvine, CA) created an increasing block structure to water pricing that reduced outdoor water consumption among its users by 50% (Desena, 1998). In 1995, a comprehensive water conservation education program was started by the Albuquerque, NM Water System to reduce per capita use. This program included time-of-day for watering restrictions, odd-even street address for watering days, and promotion of xeric plants. Time-of-day violations could be fined from $20 up to $1000. This program had reduced water use in 2004 by 34% compared with 1995 figures (City of Albuquerque, 2014). The city of San Antonio, TX, has implemented a water conservation program over the previous 20 years which can be described as remarkable. Despite a 67% increase in population, San Antonio’s current water use is very near to what the water use was in 1984 (Postel, 2011). Most of the San Antonio Water System Management Plan places emphasis in landscape irrigation, which include outreach education, time-of-day, and day-of-week irrigation. These programs provide fine examples for other municipalities to emulate and adapt. However, research-based results and outreach education will still be needed for landscape water use efficiency and conservation in amenity landscapes. This may include smart-irrigation controllers, alternative water sources, use of native and adapted plants, and mixed landscape crop coefficients (Cabrera et al., 2013; McCready et al., 2009; Pannkuk et al., 2010; Parsons et al., 2010).
Landscape irrigation based on mixed species crop coefficients is an emerging area of water conservation based on climatological conditions. Crop coefficients for irrigation exist for most turfgrass species and a few woody ornamental species, but crop coefficient type irrigation information on amenity landscapes with mixtures of two plant types is quite limited (Pannkuk et al., 2010). Urban landscapes are a heterogeneous mosaic of plant types that are managed in patches (Stabler, 2008). Further studies are needed to provide refinement to a mixed species landscape coefficient suitable to specific regions (Cabrera et al., 2013). The American Society of Agricultural and Biological Engineers (ASABE) has recently defined mixed-species landscape water use normalized to reference evapotranspiration as plant factors, rather than crop coefficients (ASABE, 2012; Beeson et al., 2014; Sun et al., 2012a). The new S623 Standard attempts to define landscape water use requirements nationally across various humidity zones (Beeson et al., 2014).
The mixtures of plant forms in landscapes (grasses vs. woody plants) may also influence the amount of water entering soil and percolating downward to potentially recharge groundwater. Beard and Green (1994) summarized benefits of turfgrasses to groundwater recharge and surface water quality. Groundwater recharge is generally greater in areas of annual crops and grasses than it is in areas of trees and shrubs (Prych, 1998). Allison et al. (1990) demonstrated an impact of vegetation in Australia where deep-rooted eucalyptus (Eucalyptus sp.) trees were replaced with shallow-rooted crops resulting in recharge increases of about two orders of magnitude. Therefore, as recharge is evaluated, there is some dependence on land use/land cover. Irrigated areas contribute to water returned to soil for groundwater flow and may have a significant impact on recharge.
There is growing interest in use of ETo data from weather stations for irrigation recommendations in amenity landscapes. Therefore, objectives of this study were to determine PFs of model landscapes composed of mixed turfgrass and shrub species, and determine any seasonal effects on PFs. Second, as a result of irrigation in amenity landscapes with various plant forms, amounts of leachate were measured in each plant combination. Water percolating downward and potentially recharging groundwater in amenity landscapes has not been measured in previous work; therefore, this research would address this gap in literature.
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