Real-time nitrogen management in rice using leaf color chart (LCC): A review

Efficient nitrogen (N) management is critical for achieving optimal rice productivity and minimizing environmental degradation ^[1] (Fageria & Baligar, 2005). Traditional blanket N application often results in either excessive or insufficient use of fertilizer, leading to economic losses and ecological harm ^[2] (Dobermann & Cassman, 2002). The Leaf Color Chart (LCC) has emerged as a low-cost, farmer-friendly tool for real-time N management by allowing visual estimation of leaf nitrogen status ^[3] (Alam et al., 2005). It enables site-specific and time-specific N applications, thereby improving nitrogen use efficiency (NUE) and reducing N losses ^[4] (Singh et al., 2002). Numerous field studies have shown that LCC-guided N application can sustain or even increase rice yields while using less fertilizer ^[5] (Buresh et al., 2010). Compared to sensor-based tools and decision support systems, the LCC is simpler, more accessible, and highly effective for smallholder farmers, especially in Asia ^[6] (Balasubramanian et al., 2000). Despite its potential, challenges such as user subjectivity, regional calibration needs, and lack of awareness still hinder widespread adoption ^[7] (Bijay-Singh et al., 2002). This review summarizes the evolution, efficacy, limitations, and innovations in LCC-based nitrogen management for rice, aiming to identify research gaps and future directions for its broader adoption in sustainable agriculture.