English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Sustainable use of water resources is of increasing importance in container plant production as a result of decreasing water availability and an increasing number of laws and regulations regarding nursery runoff. Soil moisture sensor-controlled, automated irrigation can be used to irrigate when substrate volumetric water content (u) drops below a threshold, improving irrigation efficiency by applying water only as needed. We compared growth of two Gardenia jasminoides cultivars, slow-growing and challenging ‘Radicans’ and easier, fast-growing ‘August Beauty’, at various u thresholds. Our objective was to determine how irrigation can be applied more efficiently without negatively affecting plant quality, allowing for cultivar-specific guidelines. Soil moisture sensor-controlled, automated irrigation was used to maintain u thresholds of 0.20, 0.30, 0.40, or 0.50 m·m. Growth of both cultivars was related to u threshold, and patterns of growth were similar in both Watkinsville and Tifton, GA. High mortality was observed at the 0.20-m·m threshold with poor root establishment resulting from the low irrigation volume. Height, width, shoot dry weight, root dry weight, and leaf size were greater for the 0.40 and 0.50 m·m than the 0.20 and 0.30-m·m u thresholds. Irrigation volume increased with increasing u thresholds for both cultivars. For ‘August Beauty’, cumulative irrigation volume ranged from 0.96 to 63.21 L/plant in Tifton and 1.89 to 87.9 L/plant in Watkinsville. For ‘Radicans’, cumulative irrigation volume ranged from 1.32 to 126 L/plant in Tifton and from 1.38 to 261 L/plant in Watkinsville. There was a large irrigation volume difference between the 0.40 and 0.50-m·m u thresholds with little additional growth, suggesting that the additional irrigation applied led to overirrigation and leaching. Bud and flower number of ‘Radicans’ were greatest for the 0.40-m·m u threshold, indicating that overirrigation can reduce flowering. The results of this study show that growth of the different G. jasminoides cultivars responded similarly to u threshold at both locations. Similarities in growth and differences in irrigation volume at the 0.40 and 0.50-m·m u thresholds show that more efficient irrigation can be used without negatively impacting growth. More efficient irrigation management has become a focus in sustainable container plant production (Chappell et al., 2013a) to improve resource use and to mitigate the environmental impact of fertilizers and pesticides found in nursery effluent (Beeson et al., 2004; Bilderback, 2002; Lea-Cox and Ross, 2001). Best management practices such as cyclic irrigation, grouping plants based on water needs, and runoff collection basins are effective methods of improving irrigation (Chappell et al., 2013a) but do not control irrigation based on actual crop water requirements. Approaches to irrigation control based on substrate volumetric water content and/or daily water use (DWU) apply only the water needed by the crop to replace what is lost resulting from evapotranspiration and can provide greater efficiency (Bayer et al., 2013; van Iersel et al., 2010; Warsaw et al., 2009). Irrigating based on q and DWU requires knowledge of a diversity of ornamental plant water requirements, which is currently limited (Warsaw et al., 2009). Understanding how plant growth is affected by maintenance of different q thresholds will allow for species-specific guidelines. Automated irrigation using capacitance sensors to maintain q thresholds can be used to grow plants at different levels of water availability, allowing for determination of thresholds at which growth is negatively impacted. Irrigation volume can be reduced using q threshold control while still producing salable plants for a variety of ornamental crops including Hibiscus acetosella ‘Panama Red’ (Bayer et al., 2013), Gaura lindheimeri ‘Siskiyou Pink’ (Burnett and van Iersel, 2008), Hydrangea macrophylla ‘Mini Penny’ (van Iersel et al., 2009), and Lantana camara (Bayer et al., 2014). To date sensor-controlled automated irrigation has largely been used in research; however, wireless sensor networks capable of controlling irrigation are being developed for practical implementation in commercial production (Kohanbash et al., 2013) and have been trialed in nurseries (Belayneh et al., 2013; Chappell et al., 2013b). Management of irrigation water can also be beneficial for reducing the spread of soilborne pathogens. Losses resulting from soilborne pathogens can be 30% for problem crops such as dwarf gardenias (Gardenia jasminoides ‘Radicans’ and ‘MADGA 1’), which are high-value yet problematic crops for many growers (Chappell et al., 2013b). Phytophthora cinnamomi was among the most prevalent pathogens in Gardenia jasminoides production at a commercial nursery in Georgia (Chappell et al., unpublished results). Control of q has been shown to reduce pathogen pressure and disease incidence not only limiting losses, but also reducing the need for pesticide applications (Chappell et al., 2013b). Economic analysis of wireless sensor network-controlled irrigation and standard nursery irrigation practices in a commercial nursery in Georgia found shortened production time, 50% reduction in loss resulting from disease, and reduced fertilizer and fungicide applications, which resulted in a 20.6% increase in profits (Lichtenberg et al., 2013). Greater allocation of resources to root development vs. shoot growth in waterlimited conditions has been reported as a plant adaptation for survival (Kozlowski and Pallardy, 2002; Silva et al., 2012). Although the impact of soil moisture sensor-controlled irrigation on shoot growth is well known, information is limited on the effects on root growth (Bauerle et al., 2013). Bauerle et al. (2013) found that root distribution affected substrate moisture measurements in containergrown tree species with greater variability with greater biomass and/or coarser roots. An understanding of how root growth is affected by q is valuable not only for container plant production, but also the establishment of plants in the landscape. Comparing the growth of Gardenia jasminoides ‘August Beauty’ and ‘Radicans’ grown at various q thresholds will provide further information about how irrigation can be applied more efficiently without negatively impacting plant quality. On-farm trials have shown that sensor-controlled irrigation can prevent root disease problems in Gardenia jasminoides and shorten the production cycle (Chappell et al., 2013b). However, there has been no research to determine the optimal q threshold for Gardenia jasminoides. This study compared growth of more challenging Gardenia jasminoides ‘Radicans’ and faster-growing, less problematic Gardenia jasminoides ‘August Beauty’. The objectives of this study were to see if both cultivars exhibit similar growth responses to Received for publication 12 Aug. 2014. Accepted for publication 20 Nov. 2014. The research was funded by USDA-NIFA-SCRI (award no. 2009-51181-05768). We thank Sue Dove for her assistance with this research and McCorkle Nurseries for supplying plant material and substrate. We thank Bob Teskey, Matthew Chappell, and Sheryl Wells for their suggestions on the manuscript. To whom reprint requests should be addressed; e-mail mvanier@uga.edu. 78 HORTSCIENCE VOL. 50(1) JANUARY 2015 Fig. 1. Substrate volumetric water content (lines) and rain (bars) over the course of the 191-d Tifton (right graphs) and 190-d Watkinsville (left graphs) experiments. Gardenia jasminoides ‘August Beauty’ (upper graphs) and ‘Radicans’ (lower graphs) were irrigated when substrate volumetric water content dropped below the irrigation threshold (0.20, 0.30, 0.40, 0.50 m·m). Drying of substrates to q thresholds after rain events was generally achieved within days for both experiments. Fig. 2. Cumulative irrigation volume for the production of Gardenia jasminoides ‘August Beauty’ and ‘Radicans’ as a function of the volumetric water content thresholds at which irrigation occurred over the course of the 191(Tifton) or 190-d (Watkinsville) period. Cumulative irrigation volume increased with increasing volumetric water content threshold (P = 0.0001). Data were log-transformed before analysis to account for differences in variance among treatments. Trendlines represent quadratic regression curves for ‘August Beauty’ and cubic regression curves for ‘Radicans’. HORTSCIENCE VOL. 50(1) JANUARY 2015 79 q levels, to compare shoot vs. root growth, and to determine whether q affects the susceptibility of plants to Phytophthora cinnamomi. Materials and Methods Research was conducted at the University of Georgia Horticulture Farm in Watkinsville, GA, from 4 May to 9 Nov. 2011 and at the University of Georgia Tifton Campus from 18 Apr. to 25 Oct. 2011. The studies were conducted at two locations to compare plant responses under different environmental conditions. Plant material. Gardenia jasminoides ‘August Beauty’ and ‘Radicans’ in 3.8-L black plastic containers were obtained from McCorkle Nurseries (Dearing, GA) on 5 Apr. 2011. Plants were grown in a pine bark substrate with 1.97 kg·m lime, 0.74 kg·m Micromax (Everris, Dublin, OH), 0.74 kg·m gypsum, and 1.98 kg·m of controlled-release fertilizer (Osmocote Pro 18-6-12; 18.0N–2.6P– 10.0K; Everris, Dublin, OH). Plants were kept well watered for 2 or 4 weeks (Tifton and Watkinsville, respectively) to allow for root establishment of the recently transplanted cuttings. Treatments and data collection. Identical soil moisture sensor-controlled irrigation systems, based on that described by Nemali and van Iersel (2006), were used in both locations. Both locations had 16 plots with plots being experimental units consisting of 18 to 20 plants. Soil moisture sensors (10HS; Decagon Devices, Pullman, WA) were inserted into two pots in each of the 16 plots at an 45 angle. Sensors were inserted with the prongs extending into the center of the substrate to a depth at which t

Automated Irrigation Control for Improved Growth and Quality of Gardenia jasminoides ‘Radicans’ and ‘August Beauty’