Application of low-cost soil moisture sensors for irrigation management in Brassica oleracea var. acephala cultivation

• Calibration confirmed the viability of SKU: CE09640 for soil moisture estimation. • RGB LEDs enabled intuitive soil moisture feedback for low-literacy farmers. • The sensors responded consistently to field soil moisture variations in kale. • No significant differences between low-cost and conventional irrigation management methods. • The system is low-cost, patentable, and suitable for resource-limited contexts. Water scarcity demands efficient irrigation, yet conventional technologies remain inaccessible to low-income farmers. Low-cost, easy-to-use sensors represent a promising alternative. This study develop and evaluate a soil moisture monitoring system using low-cost capacitive sensors (SKU: CE09640) integrated with an Arduino microcontroller, featuring RGB LED alerts to indicate soil water status. Field validation was conducted in kale ( Brassica oleracea var. acephala ) cultivation, comparing three irrigation management (IM) strategies: crop evapotranspiration (ETc), tensiometers (IMT), and capacitive sensors (IMC). Sensors were calibrated in the laboratory using the gravimetric method. The experiment followed a randomized block design in a 4 × 3 factorial scheme, with four irrigation levels (50 %, 75 %, 100 %, and 125 % of the irrigation depth estimated by each method). Number of commercial (NCL) and non-commercial leaves (NNCL), fresh weight (FMML), number of mature leaves (NML), and water use productivity (WUP) were evaluated. Calibration results showed a strong inverse correlation ( R < -0.964), high fit (R 2 > 0.95), and acceptable accuracy (RMSE < 0.05) in predicting soil moisture compared to gravimetric method. Field validation revealed no significant interaction between factors and similar performance among IM strategies for most variables. ETc-based IM showed the highest WUP (12.42 g l -1 ), followed by IMC (10.95 g l -1 ), and IMT (9.82 g l -1 ), indicating that the SKU: CE09640 sensors enables greater water savings than conventional devices like tensiometers. The findings support the use of SKU: CE09640 sensors is a viable, accessible solution for IM, promoting efficient water use and benefiting smallholder farmers with limited educational backgrounds or technical training.