Terminology of relative nutrient status of soil

The relative nutrient status of a plant may be easily described using the following terms:

Deficiency range
Nutrient deficiencies occur in plants when an essential element is not taken up by the plant in sufficient amounts. As a result, yield will be limited by the element which is deficient. While slight to moderate deficiencies do not always result in visual deficiency symptoms, distinct visual symptoms appear in severe cases.

Critical range
Below the critical range of nutrients, an addition of the essential element will trigger an increase in yield. Above the critical range, the levels of essential nutrients are considered sufficient.

Sufficiency range
Within this range, additions of the essential nutrient will not result in any increase in yield. However, uptake of the nutrient may continue. Thus, the concentration of that essential nutrient in plant tissue will also increase. We refer to the uptake of an essential nutrient within the sufficiency range as luxury consumption.

Toxicity rangeToxicities occur when an essential (or nonessential) element is taken up in great enough quantities to actually reduce plant growth. As a result, toxicities can severely limit yield.