Frequent and excessive irrigation of landscape ornamentals can contribute to depletion of potable water supplies. Rapid population expansion and drought in parts of the United States have water management officials concerned that demands for water will exceed supply (Archer, 2002). Water consumption and corresponding percolate leaching may be significantly reduced in annual landscape beds through cultural practices such as the addition of soil amendments or use of conservative irrigation practices.
Incorporation of organic matter or compost in annual landscape beds is widely recommended to improve water and nutrient-holding capacities, particularly in sandy soils (Warren and Fonteno, 1993). However, organic matter is highly variable depending on source, can rapidly decompose, and can pose as a potential source of weed seed. An alternative soil amendment for sandy soils is clay, which possesses physical and chemical properties that increase water and nutrient-holding capacities. Calcined clays have successfully been used to reduce daily irrigation volumes in herbaceous and woody plant production (Cantliffe, 1989; Owens et al., 2003). However, calcined clays can be cost-prohibitive in the landscape environment. Mined field clay may function as a feasible economic solution for sandy soils.
Intensive management of irrigation frequency and application method can significantly decrease landscape water use. Most automated landscape irrigation is controlled by preprogrammed time clocks that use rigid scheduling without regard for available soil moisture or plant water requirements. This is especially true of residential landscapes. Furthermore, irrigation recommendations are inconsistent with application frequencies and rates varying among sources. This combination of factors often results in overirrigation in residential and commercial landscapes.
Soil moisture sensors are available that control irrigation as a function of available soil moisture. Tensiometer-regulated irrigation systems have resulted in significant reductions in irrigation volumes during production of Rosa hybrida L. ‘Kardinal’, Prunus persica (L.) Batsch ‘Cresthaven’, and Cucumis sativus L. without compromising quality or growth (Ells et al., 1989; Huslig et al., 1993; Oki et al., 2001). Tensiometers programmed to irrigate at 50% of plant-available water reduced irrigation volumes applied to Petunia × hybrida ‘Midnight’, but aesthetic quality and canopy size were compromised in simulated landscapes (Scheiber and Beeson, 2006). Qualls et al. (2001) used granular matrix soil moisture sensors to reduce average application volumes by greater than 20% in mixed residential landscapes. Dielectric probes and tensiometers reduced irrigation volumes in turfgrass without compromising growth or quality (Dukes et al., 2005; Synder et al., 1984).
Objectives of this study were to: 1) quantify irrigation requirements of an annual bedding plant in simulated landscape beds in response to tensiometer-controlled irrigation for differently amended soils, 2) evaluate growth responses and aesthetic quality of an annual bedding plant in relation to different soil amendment practices, and 3) determine feasibility of field clay as an amendment for sandy soils to decrease irrigation requirements.
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