Critical Concentrations
Critical nutrient concentrations are the different relations that exist between plant growth rates (yields) and nutrient supply and concentrations in the plant tissue (uptake). Some of the very important relations are as follows:
Nutrient absorbed by a plant, and the plant’s growth and/or yield. This would show the “critical level” or optimum concentration of an element” for a given crop, maximum growth or yield occurs at this level. Plants found to contain amounts of an element below this level are considered deficient.
Critical concentration shows the minimum tissue concentration required for maximum yield or crop quality, or the concentration of a nutrient in a particular plant part sampled at a particular growth stage at which yield is maximum.
The optimum nutrient yield and optimum nutrient concentration for most crops could be plotted or expressed as a range rather than as a point on yield curve. Ranges are expressed as low, sufficient, or adequate, high and excessive or toxic.
Additional plant characteristics such as variety or hybrid, environmental conditions such as soil moisture, temperature light intensity and quality, and interactions with other nutrients, can alter the relationship between concentration and plant response, e.g. the interaction between K and Ca/Mg concentrations in corm leaf.
Plant Nutrient Analysis as a Diagnostic Tool: The nutrient concentration in the plant tissue e.g. the leaf, can be shown to be directly related to the quantity of the elements available in the soil (i.e. soil fertility), to the quantity applied as fertilizer and to plant growing (yield).
Minimal percentage: This is a narrow range. Within the range, yield or response may increase while the elemental concentration is constant. Symptoms of deficiency are clearly evident.
Poverty adjustment stage: This is where an increase in elemental concentration results in increased response (growth/dry matter yield). Response could be initially linear but later increasing at a decreasing rate.
Read Also: Characteristics of Soil Analytical Methods for Practical Advisory Work
Critical nutrient Percentage: This state is regarded as ideal for production. The critical nutrient percentage is the range below which response is sub-optimum, at which it is optimum, and above which there is luxury consumption.
Luxury Consumption Range: This is the range at which plant response (Dry matter accumulation) remains constant while the tissue nutrient concentration continues to increase.
Toxicity Range: After the luxury stage there may set in the toxicity stage where further increases in the tissue elemental concentrations result in a depressed response.
Other Growth Response Terminologies
Separation of Deficient from non-Deficient: The level of an extractable nutrient in soil that separates the deficient from the non-deficient is call the critical level.
Percent yield: Where soil may differ in its productive potential or where environmental conditions may be different, the yield for the treatment not receiving the nutrient being studied is calculated as a percentage of the yield with the nutrient added. The soil test is then calculated against the percent yield.
Read Also: General Purpose of Plant Analysis as a Diagnostic Tool
