**6.2. Deviation from the percentage optimum**

**1.** In the deficient range or zone the symptoms are visible and occur in soils (or substrates) very deficient in an element due to insufficient dosages. In these conditions the re‐ sponse in production of dry matter is high, the element concentration is not increased and it may even be diluted. The nutrient dilution effect caused by organic matter forma‐ tion is known as the Steembjerg effect. When the concentration of a plant nutrient is set

**2.** In the transition range or zone, deficiency symptoms are not visible (disguised hunger) but there is a direct relation between nutrient foliar concentration of and production. When the nutrient concentration allows an average of 80 to 95% of the maximum pro‐ duction, this level corresponds to the critical level. The relation of nutrient concentra‐ tions and maximal production (100%) is seen in soils (or substrates) with slight deficiency and with lower responses in growth and production when the nutrient is ap‐ plied. In these conditions the increases in foliar concentrations are proportional to growth and production, that is, greater absorption is compensated by increasing organ‐ ic material. A nutrient concentration in this range, considered between the critical level

**3.** In the luxury consumption range or zone, increasing element concentration does not in‐ crease production. This is observed in non-deficient soils receiving element dosages. Although plant tissues show absorption of the increased nutrient concentrations this is not expressed in increased growth. Thus, the element concentration in this range, which corre‐ sponds to maximal or optimal production and it is below the toxicity critical point, is consid‐

**4.** The toxicity range or zone starts when increased nutrient concentrations significantly reduce production. Reductions of 5% up to 20% indicate toxic levels. The condition is observed in soils (or substrates) with excess nutrients receiving additional dosages that are absorbed as shown by increased tissue concentrations but expressed in decreased

The critical level of deficiency is a factor largely employed in research and it corresponds to an optimal nutrient concentration. Below it the growth index (production or quality) is sig‐

After attaining maximal production, increased nutrient concentrations will not result in growth but in plant "luxury consumption". During this period nutrients accumulate in cell vacuoles and may be gradually liberated to supply eventual plant nutritional necessities. As already stated nutrient concentrations above the level of luxury consumption can lead to de‐

Interpretation of foliar nutrient concentrations based on the critical level and the sufficiency range is made directly by comparison with standard values. The plant nutritional status (de‐ ficiency, sufficiency, luxury consumption) is defined independently for each element by the range of values found for the sample. However, the plant mineral composition is the result of its adaptation to an environment under the action of several limiting factors. Lack of con‐

in this range it is considered deficient.

ered to be high.

128 Soil Fertility

and maximal production is interpreted as adequate.

growth and/or imbalance in relation to other nutrients.

creased production and characterize the toxicity range.

nificantly decreased and above it, production represents poor economics.

The deviation from the percentage optimum (DPO) is an improvement of the critical level method [19]. It evaluates each nutrient concentration in relation to the optimum value (me‐ dian of the sufficiency range) by the expression: DPO= [(Cx100/CR)-100] where C is an ele‐ ment concentration in the sample dry matter and CR it is the optimal concentration for the same conditions (culture, tissue analyzed, manipulation, plant development stage etc.). In the absence of the sufficiency range the critical level is taken as the optimum value.

This is a procedure not common in the literature but it permits the evaluation of the nutri‐ tional status of the plant and the arrangement of the elements as a function of the degree of deficiency. However, the limitation order is not representative because element interactions are not considered and the conventional table is still used.

### **6.3. Diagnosis and Recommendation Integrated System (DRIS)**

DRIS is an alternative to the conventional method for the determination of the nutritional status of a plant [20]. It considers nutrient interactions in the diagnostic process, which is conducted by the combination of all the relations in the form of ratios [20] or products [21]. In this technique indexes, which express nutrient equilibrium in a plant or culture are calcu‐ lated for each one, as a function of concentration ratios of each element and the total and compared in groups of two to other ratios considered standard or norms obtained in a pop‐ ulation of highly productive plants.

Foliar diagnosis, in this method, aims to adjust fertilization, so far only recommended by soil fertility and culture productivity, by additional production gains and correction of defi‐ ciencies. It also makes possible the management other nutrient availabilities, possibly reduc‐ ing them and permitting an equilibrated fertilization, in view of the culture nutritional necessities.

### **6.4. Diagnosis of nutritional composition (DNC)**

The method relates nutrient concentrations in a multivariable form, as a function of ratios of each nutrient concentration and the geometrical mean of the nutritional composition of the sampled tissue [23]. The method is not widely used although it deals with relations between all elements analyzed.

DNC and DRIS are independent calibration methods, since use of double or multi variable methods minimizes non controlled effects of accumulated biomass, in contrast to the critical level, which needs calibration assays conducted in places and different years, and maintain control on other production factors (including other nutrients) and on a supply adequate to full plant development [24].

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 steps.

**•** Deficiency symptoms may be different from the ones described in the literature or speci‐ alized publications. For example, symptoms may be light instead of the severe ones de‐

**•** Element deficiency signs may be different according to element and culture. Zn defi‐ ciency in fruit trees is expressed by smaller leaves and in corn cultures, new leaves

**•** Deficiency symptoms may be similar for different nutrients.

**•** Deficiencies of two or more nutrients prevents identification.

**•** Certain deficiencies may reduce production without plant symptoms.

**•** Excess of one nutrient may be mistakenly taken as the deficiency of another one.

**•** Adequate visual diagnosis must be conducted by technicians with significant experience

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

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

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.

in va‐

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http://dx.doi.org/10.5772/53388

**•** Visual diagnosis does not quantify neither the deficiency level nor the excessive one.

scribed.

are bleached.

in cultures of the region.

only as complement.

**8. Other methods**
