This protocol outlines the quantification of total phosphorus concentration in leaf material through Kjeldahl digestion and flow injection analysis. This method utilises a traditional Kjeldahl digestion as an alternative to microwave digestion which is utilised in the protocol “Quantification of Total Phosphorus Content in Plant Material Using Microwave Digestion and Segmented Flow Analysis”. The Kjeldahl digestion is more accessible in most laboratories than microwave digestion. The digestion phase converts phosphorus into orthophosphate which reacts with ammonium molybdate and ascorbic acid during flow analysis to form a blue complex which can be measured spectrophotometrically. Phases of analysis include acid digestion using a Kjeldahl digestion (1.5 days); the preparation of reagents (2 hours) and finally analysis for total phosphorus on the flow analyser (30 minutes plus 90 seconds per sample).