Leaf Colour Chart–guided Nitrogen Management in Cereal Systems: Yield, Efficiency and Sustainability

Nitrogen fertilisation is essential for cereal production, but fixed rates and schedules frequently fail to reflect field-to-field variation in indigenous soil supply and crop demand. The leaf colour chart (LCC) is a low-cost, visually interpreted proxy for crop nitrogen status that can guide in-season fertiliser application without specialised electronic equipment. This critical narrative review examines physiological validity, chart calibration, field performance in rice, wheat and maize, nitrogen-use efficiency, environmental effects, adoption constraints and digital extensions. Peer-reviewed experimental and contextual evidence was critically compared according to crop and genotype, chart threshold, dose per application, baseline management, study design and outcome measurement. The most consistent findings support the ability of locally calibrated chart rules to adjust nitrogen topdressing and, in systems where conventional practice oversupplies fertiliser, preserve yield with reduced input. Results are less uniform across cereal species, cultivars and establishment methods. Maximum grain yield, highest nitrogen-use efficiency and largest economic return often occur at different threshold-and-dose combinations. Chart colour is affected by leaf morphology and non-nitrogen stresses, creating a risk of incorrect fertiliser recommendations if interpreted in isolation. A smaller evidence base supports reductions in directly measured environmental losses under specific management conditions; changes in applied nitrogen alone do not demonstrate lower greenhouse-gas emissions or leaching. On-farm implementation requires consistent sampling, viable labour arrangements and locally trusted advice, while digital colour analysis requires independent validation of both measurement and fertiliser decisions. The review identifies priority needs for external threshold testing, dose-matched comparisons, long-term soil and nutrient balances, direct environmental monitoring and prospective farmer-adoption studies. Leaf colour charts offer a practical contribution to evidence-based nitrogen stewardship when treated as calibrated decision aids rather than universal predictors of sustainable yield gains.