**8. Other methods**

However, it is important to emphasize that all methods that interpret foliar analysis re‐ sults are based on analysis of nutrient concentrations in plant dry matter. Thus, all pro‐ cedures described in the previous topics (excluding biotic and abiotic factors that may interfere in the collection, preparation and analysis of sample and results) should be well conducted, since no analytical or interpretative method will correct mistakes in these

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‐

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

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

Nutritional deficiencies rarely appear only in some plants.

symptoms similar to nutritional deficiency.

**1.** Dispersion- nutritional problems usually occur in the fields in a homogeneous form. In cases of pest/diseases the occurrence may be limited to isolated plants or dense growth.

**2.** Simetry- nutritional disorders usually occur symmetrically in leaves while phytopatho‐ genic or insect injuries provoke asymmetrical symptoms with the exception of the ones caused by viruses, which translocate though the whole plant and may produce foliar

**3.** Gradient- in a plant or branch the symptoms appear in a gradient, becoming more se‐ vere going from old to young leaves or in reverse, according to the element mobility in

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‐

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‐

**•** In the field the plant may suffer from interfering agents (pests and pathogens) that mime‐

rosis or leaf spots; c) interrib chlorosis; d) necrosis; e) red color; f) deformities.

tize nutritional deficiency symptoms, as already stated.

steps.

130 Soil Fertility

**7. Visual diagnosis**

ity described in the literature.

producing similar symptoms.

the plant.

thors as described in [17].

Foliar diagnosis is a direct evaluation method that utilizes nutrient concentrations in plant tissues as an indicator of nutritional status. However, indirect methods exist and are useful. When a deficient nutrient is part of an organic component or activates an enzymic activity this can be indirectly expressed. For example N deficiency may be shown by low chloro‐ phyll levels or low activity of nitrate reductase. A description of biochemical tests that may be employed to evaluate plant nutritional status has been reported in [8]. For N, reductase and glutamine synthetase activity, amide N and asparagine; for P, fructose-1,6-diphosphate and photosynthesis ; phosphatase activity; for K,amide concentrations; free amino-acids; for Mn, peroxidases and a/b chlorophyll ratios; for B, ATP-ase activity; for Zn, ribonuclease, car‐ bonic anhydrase, arginine concentration. In the case of P other studies indicate that Pi in va‐ cuole cells may indicate the nutritional status of the plant [25, 26]. These are additional tools to evaluate plant nutrition, which are not commonly used because some of the tests require special methods of sampling, storage and complex analytical procedures and costly equip‐ ment. Other methods, specifically for N, evaluate the index of green color by a portable de‐ vice called chlorophyll meter. This index is strongly correlated to the chlorophyll concentration in leaves and N nutritional status of the plant.
