Multinutrient diagnosis of nitrogen status in plants

The nitrogen (N) status of conifer seedlings, onion, and potato was diagnosed using the Critical Value Approach and the Compositional Nutrient Diagnosis (CND). The multinutrient CND N indices (In) accounted for the phosphorus (P) and potassium (K) concentrations in tissues. For conifer seedlings, a linear‐plateau relationship with well defined deficiency and excess zones was shown between dry matter yields and In, while the yield‐N response curve was distorted. The yield‐In relationship for onion and potato was improved as compared to the yield‐N curve. Correlation coefficients with yields were higher for In values than for raw concentration values. Critical In values were ‐1.8 for conifers, ‐0.8 for potato, and ‐0.7 for onion.