Contamination of groundwater supplies with nitrates from agricultural endeavors has been a concern for decades. Booming residential and commercial development has turned attention to nitrate leaching from commercial and residential lawns (Campbell and Sargent, 2002). Nitrate leaching from turfgrass has been widely researched, and increased nitrogen losses after irrigation have been reported (Brown et al., 1977; Morton et al., 1988; Snyder et al., 1984). However, few studies have examined nitrogen losses from newly planted or established landscapes (Erickson et al., 2001; Geron et al., 1993; Gross et al., 1990). Annual flower beds are an intensely managed portion of the landscape that require frequent applications of water and fertilizer and provide an additional origin for nonpoint source pollution (Campbell and Sargent, 2002).
Despite regulations aimed at water conservation and reductions in nonpoint source pollution, water management districts within Florida regulate irrigation frequency but not application volumes. Thus, total volume applied can vary in magnitude and potentially result in overirrigation. Several studies conducted on trees, shrubs, and herbaceous perennials have demonstrated that irrigation frequency affects growth in the landscape. Aesthetic quality and shoot or root dry weight decreased for several perennial species as irrigation frequency declined from weekly to every 4 weeks (Zollinger et al., 2006). During landscape establishment, canopy size and dry weight of Viburnum odoratissimum Ker-Gawl (sweet viburnum) increased as irrigation frequency increased from once every 4 d to 2 d (Scheiber et al., 2007). Gilman et al. (1998) reported frequent irrigation of Quercus virginiana Mill. (Live oak) accelerated establishment in comparison with trees irrigated infrequently. Irrigation quantities in these studies were not changed during the experiments.
Many investigations into irrigation and plant establishment applied equivalent volumes at each irrigation. Such methods make discernment between effects of irrigation frequency and quantity on growth difficult. To make the distinction, Paine et al. (1992) and Stabler and Martin (2000) applied equivalent total volumes at different frequencies using reference evapotranspiration. Paine et al. (1992) reported irrigation frequency had no effect on mortality rates or aesthetic quality of several woody ornamentals. Stabler and Martin (2000) found increased irrigation frequency increased growth but decreased water use efficiency.
The objectives of this study were to: 1) evaluate growth responses and leaf gas exchange of the annual bedding plant coleus in relation to irrigation frequency and quantity, 2) develop and examine water budgets for each irrigation regime, and 3) determine leaching potential of nitrates from fertilizer-amended annual flower beds in response to various irrigation frequencies and quantities.
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