Sensor-based Irrigation in Different Sweet Pepper Varieties in the U.S. Virgin Islands

Sweet peppers are widely produced in the Caribbean islands. Farmers usually water the plants without using the proper water management techniques. Soil-based monitoring systems can be used to improve water use efficiency and save water resources. Our study evaluated the use of low-cost open-source equipment to control irrigation and the potential yield of sweet pepper varieties in the U.S. Virgin Islands. We tested two soil volumetric water contents (VWC) to trigger irrigation (0.32 and 0.42 m³/m³) and six sweet pepper varieties (‘Aristotle’, ‘Declaration’, ‘Intruder’, ‘Jupiter’, ‘Colossal’ and ‘Vanguard’), in a CRD with three replications, totaling 36 experimental units. Plants were transplanted into a Sion clay soil and fertigated using 113 kg N/ha of a 20-20-20 soluble fertilizer (200 mg/L N concentration). We assembled three independent and fully automated irrigation systems using a Mega 2560 board (Arduino), a logging shield (Adafruit), twelve 10HS soil moisture sensors (Decagon Devices), two 5-VDC 8-module relay drivers (SainSmart) and twelve 24-VAC 2.54-cm solenoid valves (RainBird) connected to a 12/24-VDC 500-VA 31EJ02 transformer (Dayton). The power line to fed the solenoids was protected with a 3400-J 51110-SRG surge protector (Leviton). When the soil VWC dropped below the thresholds, the irrigation was turned on for 1 min. The 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. When the soil VWC dropped below the thresholds, the irrigation was turned on for 1 min. The soil moisture sensors malfunctioned due to a defective internal part, not controlling the irrigation properly. Irrigations were turned on manually every other day. The two VWC treatments were averaged, resulting in six replications per variety. Total yield ranged from 13,514 (‘Declaration’) to 16,940 kg/ha (‘Vanguard’). However, the total and marketable yield did not differ among varieties (p>0.05). Anthocyanin at 67 days after transplanting (DAP) was higher on ‘Colossal’ (18.56 ACI) compared to ‘Vanguard’ and ‘Declaration’ (12 ACI on average) (p=0.0126). Leaf chlorophyll and fruit weight, width, length and sugar content at 95 DAP were not significantly different (p>0.05). Fruit hardness was higher on ‘Intruder’ and ‘Jupiter’ (1.2 kgf) and lower on ‘Colossal’ and ‘Vanguard’ (0.96 kgf) (p=0.0012). Based on our results, fully functional sensors are necessary to control irrigation properly. All six varieties presented high yield, being suitable for cultivation in the U.S. Virgin Islands.