Water Use and Growth of Hibiscus acetosella ‘Panama Red’ Grown with a Soil Moisture Sensor-controlled Irrigation System

Abstract

Efficient water use is becoming increasingly important for horticultural operations to satisfy regulations regarding runoff along with adapting to the decreasing availability of water to agriculture. Generally, best management practices (BMPs) are used to conserve water. However, BMPs do not account for water requirements of plants. Soil moisture sensors can be used along with an automated irrigation system to irrigate when substrate volumetric water content (u) drops below a set threshold, allowing for precise irrigation control and improved water conservation compared with traditional irrigation practices. The objective of this research was to quantify growth of Hibiscus acetosella 'Panama Red' (PP#20,121) in response to various u thresholds. Experiments were performed in a greenhouse in Athens, GA, and on outdoor nursery pads in Watkinsville and Tifton, GA. Soil moisture sensors were used to maintain u above specific thresholds (0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, and 0.45 m 3 · m L3 ). Shoot dry weight increased from 7.3 to 58.8 g, 8.0 to 50.6 g, and from 3.9 to 35.9 g with increasing u thresholds from 0.10 to 0.45 m 3 · m L3 in the greenhouse, Watkinsville, and Tifton studies, respectively. Plant height also increased with increasing u threshold in all studies. Total irrigation volume increased with increasing u threshold from 1.9 to 41.6 L/plant, 0.06 to 23.0 L/plant, and 0.24 to 33.6 L/plant for the greenhouse, Watkinsville, and Tifton studies, respectively. Daily light integral (DLI) was found to be the most important factor influencing daily water use (DWU) in the greenhouse study; DWU was also found to be low on days with low DLI in nursery studies. In all studies, increased irrigation volume led to increased growth; however, water use efficiency (grams of shoot dry weight produced per liters of water used) decreased for u thresholds above 0.35 m 3 · m L3 . Results from the greenhouse and nursery studies indicate that sensor-controlled irrigation is feasible and that u thresholds can be adjusted to control plant growth.

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

“…Increasing height with increasing q threshold was also reported for Hibiscus acetosella 'Panama Red' (Bayer et al, 2013), Gaura lindheimeri 'Siskiyou Pink' (Burnett and van Iersel, 2008), and Callistemon citrinus 'Firebrand' (Á lvarez and Sánchez-Blanco, 2013). In contrast, Fulcher et al (2012) found that shoot length of Hibiscus rosa-sinensis 'Cashmere Wind' was greatest for intermediate treatments rather than high or low q treatments.…”

“…Increasing shoot dry weight with increasing q thresholds has been reported for Gaura lindheimeri 'Siskiyou Pink' (Burnett and van Iersel, 2008) and Hibiscus acetosella 'Panama Red' (Bayer et al, 2013) with salable plants produced at moderate thresholds (0.25 to 0.35 m 3 · m -3 and 0.35 to 0.40 m 3 · m -3 , respectively). Reduced irrigation volumes have been used to produce plants with minimal reductions in plant growth.…”

“…Different environmental conditions could explain the significant location effect on leaf size (P = 0.0137) with Tifton plants having larger leaves. Leaf size of Hibiscus acetosella 'Panama Red' also increased with increasing q threshold (Bayer et al, 2013). Leaf elongation is sensitive to drought stress (Lambers et al, 2008).…”

“…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).…”

“…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).…”