Development of an on-field system for rapid detection and mitigation of nitrogen stress in direct seeded rice

• Developed an on-the-go variable rate aqueous nitrogen applicator for direct-seeded rice. • Integrated multi-vegetation indices (NDVI, NDRE, RVI) for real-time nitrogen sensing. • Multi-VIs approach improved nitrogen estimation accuracy. • Achieved 22–28 % fertilizer saving, 12.28 % yield gain, and 53.69 % higher NUE. • Response time of 1.82 s and 90.62 % application accuracy ensure field-scale feasibility. Efficient nitrogen (N) management is critical for mitigating nutrient stress and ensuring sustainable rice production under resource constraints. In this study, a real-time nitrogen assessment and prescription (NAP) device was developed to optimize variable-rate N application in direct-seeded rice (DSR). The system integrated a multispectral sensor (AS7263) for continuous canopy monitoring and computed three vegetation indices namely normalized difference vegetation index (NDVI), normalized difference red-edge (NDRE) and ratio vegetation index (RVI) to assess crop N status dynamically. Three NAP units were mounted on a high-clearance vehicle to deliver aqueous urea (10 % N) through subsurface application via an inverted T-type tine assembly covering three rows simultaneously. The average system response time between sensing and fertilizer discharge was 1.82 s, enabling precise and timely nutrient delivery. Field evaluation revealed that the real-time, variable-rate system reduced N fertilizer use by 22.38 % and 28.35 % during the first and second topdressing stages, respectively, while enhancing grain yield by 12.28 % and improving nitrogen use efficiency (NUE) by 53.69 %. Furthermore, fertilizer costs were reduced by 25.44 %, reflecting both economic and environmental benefits. Operating at a forward speed of 1.83 km h -1 and sensing height of 31.44 cm, the system achieved a precision rate of 90.62 %, demonstrating its potential for stress-resilient, resource-efficient and sustainable nitrogen management in DSR cultivation.