As demands on potable water supplies increase, water management officials are seeking solutions beyond restrictions on irrigation schedules. Demand-based irrigation systems such as tensiometers monitor soil moisture levels then deliver irrigation based on plant water consumption. Without compromising growth or aesthetic quality, tensiometer-regulated systems reduced irrigation volumes applied to ‘Santorini’ carnations (Dianthus caryophyllus), cucumbers (Cucumis sativus), and ‘Kardinal’ roses (Rosa hybrida) (Ells et al., 1989; Oki et al., 2001; Taylor et al., 2004). Combined with conventional automated time clocks, tensiometers can apply irrigation volumes that maintain soil moisture at optimum levels for growth.
Sustainability is the objective of landscape maintenance, not maximum growth. Sachs et al. (1975) found that growth was closely correlated to irrigation frequency, but aesthetically, established landscape shrubs and groundcovers could be maintained at reduced irrigation levels. Termed either managed allowable deficits or regulated deficit irrigation, the concept is defined as a preset level that soil or substrate is allowed to dry before irrigation. Deficit irrigation has been successfully used in container production of red tip photinia (Photina ×fraseri), sweet viburnum (Viburnum odoratissimum), japanese privet (Ligustrum japonicum), and indian hawthorn (Rhaphiolepis indica), as well as field production of spinach (Spinacea oleracea) and spring wheat (Triticum aestivum) (Beeson, 2006; Leskovar and Piccinni, 2005; Welsh and Zajicek, 1993; Zhang et al., 2005). Significant reductions in application volumes were found with equivalent or greater growth and quality than nondeficit controls.
The concept has not been not widely used in urban environments. However, recent studies have investigated deficit irrigation responses for residential and commercial turfgrass applications. At 70% replacement of well-watered actual evapotranspiration (ETA), performance and quality of buffalograss (Buchloe dactyloides) and zoysiagrass (Zoysia spp.) grown for residential lawns were comparable with grasses receiving 100% ETA replacement (Henry et al., 2005). Furthermore, creeping bentgrass (Agrostis stolonifera), colonial bentgrass (A. capillaries), and velvet bentgrass (A. canina) irrigated at 60% to 80% replacement of 100% ETA were maintained at acceptable quality levels for golf course fairways (DaCosta and Huang, 2006). Previous research on ‘Midnight’ petunia (Petunia ×hybrida) found tensiometers programmed to irrigate at 50% of plant-available water (PAW) significantly reduced irrigation volumes, but aesthetic quality and canopy size were compromised in simulated landscapes (Scheiber and Beeson, 2006). The objectives of this study are 1) to evaluate the effectiveness of deficit irrigation controlled by tensiometers for reducing irrigation volumes and 2) to evaluate the effect of various irrigation deficits on growth and aesthetic quality of coleus.
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