2017 ASHS Annual Conference

Bark was commonly used as a substrate to grow Cymbidium orchids in commercial production. However, using the bark makes a grower use a lot of water. Thus, an alternative substrate is necessary to prepare for upcoming water shortage in the future. This study was conducted to select a suitable substrate for cultivating Cymbidium using a sensor-based irrigation system (SIS). Hydrophysical properties of substrate were examined, followed by a calibration to use with a soil moisture sensor, and finally these were applied to Cymbidium cultivation. Moisture retention curve of pine bark (PB), coconut chip (CC), coir dust (CD), and sphagnum moss (SM) was obtained using sandbox. Saturation points were nearly 0.8 m^-3∙m^-3 (v/v) for SM and CD, 0.6 m^-3∙m^-3 for CC, and 0.4 m^-3∙m^-3 for PB. PB and CC did not release much water after 1.0 and 1.5 pF, respectively, whereas SM and CD continued to release water steadily until 2.0 pF. Volumetric water content (VWC) coefficients and the difference among the substrates were investigated. Using distilled water, the VWC of each substrate was prepared at 12 levels in the range of 0.05 – 0.6 m^-3∙m^-3, and a soil moisture sensor 10HS (Decagon Devices, Pullman, WA, USA) was used to measure raw values (mV, ADC). The measured values were used to calculate VWC correction factor for each substrate by using a regression analysis. Sensor output-VWC regression equation of the substrates showed at least 0.84 or more coefficient of determination (R²). 1-year-old Cymbidium ‘Yang Guifei’ plants were transplanted from 10 cm to 15 cm (2,190 mL) pot. The SIS consisted of 10HS sensors, data logger CR1000 (Campbell Scientific Co., Ltd., Logan, UT, USA), relay controller SDM-CD16AC (Campbell Scientific Co., Ltd., Logan, UT, USA), and solenoid valves (NDJ Electric Valve, NaanDanjain Irrigation Ltd., Israel). PC spray stakes (Netafim Ltd., Co., Israel) and drip tubes were also installed. The VWC set point was 0.2 m^-3∙m^-3. When the sensor value was less than the set point, irrigation was performed every 20 minutes, and 200 mL of water per once was irrigated. During 13 weeks after transplant, the average amount of daily supplied water was 13.11, 0.06, 0.07, and 0.1 L in BA, CC, CD, and SM, respectively. The number of leaves of mother pseudobulb was continuously decreased in all substrate treatments because of root damages caused during transplanting. Similar tendency was also founded in chlorophyll content. However, there was no significant difference among net growth rates of lead pseudobulbs which were not damaged when the plants were transplanted. These results indicate that if the irrigation can be controlled precisely regardless of the type of substrate, it will be possible to greatly reduce water usage approximately 200% in Cymbidium orchids production.