A low-cost sensor-based roller weeder to support non-chemical weed control in smallholder rice systems

Abstract Mechanical weeding provides a sustainable alternative to herbicides in rice cultivation, particularly for smallholder farmers who use walking tractors. This study developed a low-cost roller-type weeder with a sensor-based system for real-time monitoring of downforce. The device was retrofitted onto a walking tractor with narrow rubber wheels, and each roller unit was fitted with strain-gauged coil springs connected to an ESP32 controller and an LCD. Field experiments were conducted in a transplanted Pathum Thani 1 rice field at Kasetsart University, Thailand, using a 2 × 3 factorial design with two travel speeds (0.34 and 0.67 m s⁻ 1 ) and three ballast-induced settings (0, 265, and 343N) at 10 and 24 days after transplanting (DAT). Downforce per unit was recorded in real-time and analyzed alongside weeding efficiency (WE) and plant damage (PD) using two-way ANOVA (n = 36). The results showed that higher downforce significantly increased WE ( p = 0.049 and 0.031), reaching up to 90% at DAT10 and 74% at DAT24, while PD remained modest and statistically non-significant at DAT24. Travel speed had no significant effect on WE or PD. These results demonstrate that real-time downforce monitoring, integrated with a low-cost roller-type weeder, can provide smallholder farmers with an effective non-chemical weed control solution, thereby reducing herbicide reliance and supporting sustainable rice production.