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

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 (theta) 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 theta 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 theta above specific thresholds (0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, and 0.45 m(3).m(-3)). 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 theta thresholds from 0.10 to 0.45 m(3).m(-3) in the greenhouse, Watkinsville, and Tifton studies, respectively. Plant height also increased with increasing theta threshold in all studies. Total irrigation volume increased with increasing theta 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 theta thresholds above 0.35 m(3).m(-3). Results from the greenhouse and nursery studies indicate that sensor-controlled irrigation is feasible and that theta thresholds can be adjusted to control plant growth.