METHODS OF DIAGNOSIS OF MINERAL NUTRITION OF PLANTS A CRITICAL REVIEW

Qualitative techniques, as visual diagnosis, are very useful to detect an individual problem, but when the visual symptom shows up, some reduction in yield has already been caused. For this reason cuantitative techniques are prefered. Among them, foliar analysis is the most important. Static criteria of interpretation compares leaf concentration for a single element respect to a norm. Several limitations arise from this approach that can be partly overcame with the use of methods that consider time and nutrient balances such as Evolutive Nutrient Balance, DRIS, DOP and others. These modern techniques are throughly discussed, as well as the source of acepted norms.

The active fractions of bioelements involves a chemical search for the most “soluble” part of a bioelement as a nutritional index. The variable effect of the chemical extraction and the lake of reference values make this method usefull only for particular purposes. Another organs can be sampled instead of leaf. This is the case of sap, which composition is a good index of the nutrients that are actually been taken by the plant in the moment of the sampling. Several deciduous fruit trees present flowers before leaves, in that case an early diagnosis can be made only considering the flower analysis.

Biochemical diagnosis respond to the criteria of essentiability for a single nutrient. Some metabolite concentrations can vary considerably for a small nutrient alteration, between deficiency and normality. Also enzimatic assays, and induction of enzimatic activity, has been proved to be very useful for particular disorders.

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