Due to decreasing water resources and increasing population and urbanization, water conservation and development of more efficient irrigation systems are critical in greenhouse and landscape water management (Nicolas et al., 2008; Niu et al., 2006a). Additionally, many crops are overirrigated in greenhouse production, which results in runoff and leaching of water and nutrients from the greenhouse into the environment. To optimize water use in greenhouse production, a thorough understanding of the amount of water needed to produce quality plants is vital. Although water requirements of food crops and turfgrass have been enumerated, data quantifying the irrigation requirements of ornamental landscape plants are minimal at present. By irrigating plants based on water requirements, water use could be reduced, and plants may be acclimated for drought tolerance in the landscape (Kozlowski and Pallardy, 2002).
Roses (Rosa hybrida L.) are some of the most popular garden plants in the world. RADrazz and Belinda’s Dream rose cultivars are well adapted to various climatic and soil conditions and provide the consumers with garden plants that require minimum fertilizer, water, and pesticides while growing in gardens or landscapes (Aggie Horticulture, 2014; MacKay et al., 2008). However, there is little science-based knowledge about the minimal irrigation required for plant growth and their responses to different SMC. Most drought studies use the drydown method to determine drought tolerance. In a cyclic drought study by Cai et al. (2012), ‘RADrazz’ and ‘Belinda’s Dream’ roses had significant reductions in Pn, gS, and E as SMC decreased from 20% to 10%. Plant responses to such cyclic drought stresses may differ from the responses to a continuous drought at stable SMC. The constant SMC can be maintained by the use of sensor technology in greenhouse production.
Conserving water and reducing the environmental impact of runoff are two important issues confronting container production in greenhouses and nurseries (Warsaw et al., 2009). With increasing cost of water and stringent legislation, and decreasing water availability, the development of efficient irrigation technology that conserves water and reduces runoff without adversely affecting crop quality is becoming increasingly important for success of container nurseries. Applying irrigation based on plant water requirements is a key concept in water-conserving irrigation scheduling (Warsaw et al., 2009). Using a real-time sensing technology to detect the substrate water status and control irrigation is a promising approach for improving sustainability of irrigation management (van Iersel et al., 2010).
The volumetric SMC is the most valuable environmental factor for automatic irrigation control (Jones, 2007). To study the growth and photosynthetic physiology of begonia (Begonia semperflorens L.) at six SMCs, Miralles-Crespo and van Iersel (2011) used time domain transmissometry sensors (TDTs) in multiple containers to control the irrigation based on container-specific SMC thresholds. The six SMCs ranged from 13.6% to 47.2%. The results showed that shoot DW of begonia increased as SMC increased, and plants had similar shoot DW at SMC higher than 34.8%. The total evapotranspiration increased linearly with SMC. With decreased SMC, begonia had significant reduction in leaf size, Pn, and gS (Miralles-Crespo and van Iersel, 2011).
Burnett and van Iersel (2008) reported that there was an increase in water use efficiency and reduction in stem length and branch numbers of gaura (Gaura lindheimeri Engelm. & Gray) with decreasing SMC (45% to 10%). In a study by van Iersel et al. (2010), a substrate moisture sensor-controlled irrigation system was developed to quantify the daily water use of petunia (Petunia ×hybrida Hort ex. Vilm) in SMCs from 5% to 40%. Lower SMC resulted in a decrease in shoot DW, leaf ψ, and ψS. There was only slight additional growth above 25% SMC. Similarly, at four constant SMCs (9%, 15%, 22%, and 32%), Nemali and van Iersel (2008) found that gas exchange, chlorophyll fluorescence, and leaf water potential were similar between 32% and 22% SMC for impatiens (Impatiens wallerana Hook.) and salvia (Salvia splendens Sell ex Roem. & Schult).
The objectives of the current study were to determine minimum water requirements and quantify the growth and physiological responses of two popular landscape roses, ‘RADrazz’ and ‘Belinda’s Dream’, grown at four different SMCs using the TDT sensors in multiple containers to control the irrigation based on container-specific SMC thresholds.
Aggie Horticulture 2014 Texas AgriLife Extension Service. Earth-Kind roses. 11 Mar. 2014. <http://www.aggie-horticulture.tamu.edu/earthkind/roses/about.html>
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