The container nursery industry is facing severe restrictions on water use (Beeson et al., 2004). Container substrate water deficits can be measured directly by weighing (Beeson, 2011; Million et al., 2010; Owen et al., 2007), indirectly with sensors (Bergeron et al., 2004; Murray et al., 2004), or simulated with models and local weather data (Beeson, 2010; Million et al., 2011). Evapotranspiration (ET)-based irrigation scheduling, designed to apply water in proportion to plant demand, is being recommended as a best management practice for conserving water [Florida Department of Agriculture and Consumer Services (FDACS), 2014]. Although research has investigated ET from containers during production (Beeson, 2010; Schuch and Burger, 1997), comparatively little research has evaluated the ability of containerized plants to capture sprinkler irrigation water. Irrigation capture is important because containers occupy only a fraction of the production area even when closely spaced and there is potential for plant canopies to influence the proportion of sprinkler irrigation water that is captured relative to that which falls unintercepted between containers.
We use the term CF to describe sprinkler irrigation capture:
Few studies were found that investigated the capture of sprinkler irrigation by container-grown plants. Beeson and Knox (1991) reported CF less than 1 for two Rhododendron species and Pittosporum tobira indicating that these three species directed water away from the container. CF was inversely proportional to plant leaf area and decreased at close container spacings. Beeson and Yeager (2003) measured irrigation capture by marketable-sized Viburnum odoratissimum, Ligustrum japonicum, and Rhododendron spp. in 23-cm-diameter containers spaced from 0 to 51 cm between containers in a square pattern. For plants spaced in this range, CF increased linearly from 0.5 to 1.2 for Viburnum odoratissimum and from 0.6 to 1.0 for Ligustrum japonicum. At the widest space, CF measurements for Viburnum odoratissimum ranged from 0.5 to 1.8 indicating considerable variation between plants. The CF for Rhododendron spp. was not greatly affected by container spacing with values ranging from 0.6 to 0.7. Although a wide range of plant sizes was not evaluated, CF was positively correlated with total plant leaf area and plant size.
Plant characteristics may affect irrigation capture. Bilderback et al. (2011) observed that plant architecture influences irrigation capture. Cotoneaster dammeri with an umbrella-shaped canopy exhibited CF = 1, whereas Gardenia jasminoides and Vitex trifolia, both with upright spreading architecture, exhibited CF = 2.5. Viburnum odoratissimum, a woody ornamental with an upright spreading habit, grown in 16-cm-diameter containers had CF measured every 3 weeks during production (Million et al., 2010). CF was equal to 1 until plant size index (average of plant height and plant width) exceeded container diameter at which time CF increased from 1 to 2.4 as plant size index increased from 16 to 20 cm to 40 to 50 cm.
The sprinkler irrigation system may also affect CF. Wobbler sprinkler heads resulted in better capture than impact sprinklers when close-spaced (51% vs. 44%) but not when separated (Beeson and Knox, 1991). Yeager and Beeson (1996) found that increasing the sprinkler nozzle height from 1.2 m to 3.6 m increased CF of trade #3 Rhododendron spp. ‘Formosa’ from 1.6 to 1.9; nozzle placements greater than 3.6 m did not increase CF.
The objectives of our experiments were to: 1) compare the irrigation capturing ability of some commonly grown ornamental plant species exhibiting a range of growth habits; 2) evaluate the effect that plant size, container diameter, and container spacing have on CF; and 3) compare irrigation capture for wobbler vs. impact sprinklers.
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