Chapter 11 - Diagnosis of Deficiency and Toxicity of Nutrients

Abstract

This chapter describes the general relationship between nutrient concentration and plant growth/yield and explores the various visual symptoms used for diagnosing the deficiency and toxicity of nutrients. It discusses various nutrient concentrations that are considered to be in the deficient, adequate, and toxic range. Fluctuations in environmental factors such as temperature and soil water content can affect the nutrient concentration of leaves considerably, which in turn can adversely affect the availability and uptake of nutrients by the roots and the shoot growth rate. Plant age, plant part, and concentrations of other nutrients also play their part in increasing the critical deficiency concentrations. Visual diagnosis provides enough information for a recommendation on type and amount of fertilizer to be used, and for this additional information related to soil pH, results of soil testing for nutrients, soil water status (dry/waterlogged), weather conditions (low temperature or frost) and the application of fertilizers, fungicides, or pesticides are acquired. A combination of histological and histochemical methods is useful in the diagnosis of Cu and P deficiencies, whereas enzymatic methods involving marker enzymes offer another approach to assess the nutritional status of plants. Enzymatic, biochemical, and biophysical methods can be very valuable if the total concentration or the soluble fraction of a nutrient is poorly correlated with its physiological availability. Chemical soil analysis indicates the potential availability of nutrients that roots may take up under conditions favorable for root growth and root activity, whereas plant analysis in the strict sense reflects only the actual nutritional status of plants. Therefore, a combination of both methods provides a better basis for recommending fertilizer applications.