Greenhouse Production of Slicing Cucumbers in the U.S. Virgin Islands

Cucumber is one of the major vegetables in greenhouse production. Little information is available regarding the cultivation of cucumbers in closed environment in the U.S. Virgin Islands. Our study evaluated the production of slicing cucumbers in greenhouse under different substrate volumetric water contents (VWC) applied using low-cost open-source microcontrollers. We tested four cucumber varieties (‘Boa’, ‘Bomber, ‘Corinto’ and ‘Summer Dance’) and three substrate VWCs to trigger irrigation (0.24, 0.36 and 0.48 m³/m³), on a split-plot CRD and three replications. Plants were transplanted into 9.45-L pots with Pro-Mix BX Mycorrhizae: perlite substrate (70%: 30%), trained on a vertical plastic line, and fertigated with calcium nitrate (150 and 140 mg/L Ca and N) and 10-30-20 peat-lite plant starter fertilizer (30 mg/L N). We assembled two independent and fully automated irrigation systems using a Mega 2560 board (Arduino), a logging shield (Adafruit), eighteen 10HS soil moisture sensors (Decagon), three 5-VDC 8-module relay drivers (SainSmart) and eighteen 24-VAC 2.54-cm solenoid valves (RainBird) connected to a 12/24-VDC 500-VA 31EJ02 transformer (Dayton). The power line was protected with a 3400-J 51110-SRG surge protector (Leviton). The system was powered using a 20-W Infinium solar panel (ML Solar) connected to a 12/24-VDC 10-A 1210RN solar charge controller (EPSolar) and two 12-VDC 7.2-Ah rechargeable batteries (Yuasa). Irrigation was installed using a manifold built with 2.54-cm PVC pipes, one solenoid valve and 1.9-cm polyethylene tubing with 4-L/h drip emitters connected to one O-ring tubing per plant. When the soil VWC dropped below the thresholds, irrigation was turned on for 1 min. The soil moisture sensors malfunctioned due to a defective internal part, not controlling the irrigation properly. Irrigation was controlled manually every other day. The three VWC treatments were averaged, resulting in nine replications per variety. ‘Corinto’ (22,436) and ‘Boa’ (20,000 kg/ha) total yield were higher than ‘Summer Dance’ (10,604) and ‘Mountie’ (10,435 kg/ha) (p=0.0001). Marketable yield was respectively 85%, 91%, 63% and 40% of the total yield (p<0.0001). Total number of fruits per plant were 9.6 for ‘Corinto’, 7.1 for ’Boa’, 4.7 for ‘Mountie’ and 3.8 for ‘Summer Dance’ (p<0.0001). Fruit width, hardness and sugar content were not significantly different (p>0.05). Fruits were shorter on ‘Boa’ (18.7) and ‘Corinto’ (19.7 cm) compared to ‘Mountie’ (24.2) and ‘Summer Dance’ (25.7 cm) (p=0.0180). Based on our results, fully functional sensors are necessary to control irrigation properly. ‘Corinto’ and ‘Boa’ are the recommended varieties for greenhouse cultivation in the U.S. Virgin Islands.