**7. Visual diagnosis**

Visual plant nutrition diagnosis aims a detailed characterization of deficiency or toxicity symptoms in a plant-problem and compare them to standard patterns of deficiency or toxic‐ ity described in the literature.

To use this diagnosis it is necessary to make sure that the problem is caused by deficiency or excess of a nutrient, and not by pests and other diseases that may "masque" the problem by producing similar symptoms.

The symptoms caused by nutritional disorder generally have the following characteristics:


In visual diagnosis symptoms of deficiency/excess may vary in cultures. Generally, deficien‐ cy signs start in older leaves for the easily distributed elements and in new leaves and shoots for elements of lower redistribution. The signs may be visualized in roots, like in con‐ ditions of Al toxicity, which induces ill-formed roots, thick and short. Visual symptoms of nutritional deficiency may be grouped in six categories: a) reduced growth; b) uniform chlo‐ rosis or leaf spots; c) interrib chlorosis; d) necrosis; e) red color; f) deformities.

The visual diagnosis method allows for fast identification of deficiencies or excesses with consequent correction of fertilization. However, it is a limited method criticized by some au‐ thors as described in [17].

**•** In the field the plant may suffer from interfering agents (pests and pathogens) that mime‐ tize nutritional deficiency symptoms, as already stated.


Furthermore, when the nutritional disorder is acute and visual symptoms of deficiency or excess are obvious and able to be differentiated a significant part of production (around 40-50%) may have been already compromised by a series of irreversible injuries to the physiology of the plant. Thus, visual diagnosis should not be used as a rule but only as complement.
