ABSTRACT Rapid acquisition of about nitrogen (N) in-season using gadgets like chlorophyll meters is promising to achieve high N fertilizer use efficiency. Two field experiments were conducted in two successive seasons (2017/2018-2018/2019) on wheat grown in a calcareous soil at West Nile Delta to define and validate critical threshold chlorophyll meter values to guide N fertilization. An increasing rate of N fertilizer was applied in the experiment conducted in the first season to establish plots with different yield potentials and to create variability in chlorophyll meter readings determined at stem elongation growth stage of wheat.The data revealed that an exponential model based on the chlorophyll meter could explain 54% of the variation in the aboveground N uptake. Cate-Nelson graph method was then used to define the critical threshold values of chlorophyll index at 95, 70 and 50 % relative grain yield of wheat. The defined chlorophyll meter values were 58.9, 54.5 and 53.2, respectively. Accordingly, a strategy to refine N application dose was suggested to be applied at stem elongation stage of wheat as guided by the meter in the second season. When appropriate prescriptive N fertilizer was applied (40 kg N fed^-1 in two unequal splits) followed by corrective dose as guided by the chlorophyll meter, the achievedN recovery efficiency was 67% compared with 53.8% by the recommendation rate (100 kg N fed^-1). This study revealed that N fertilizer could be managed more efficiently using rapid and hand-held tools like chlorophyll meter compared with the current general recommendation.