The location of symptoms of nutrient deficiencies within plants will depend on the extent and rate of retranslocation of the nutrient from old leaves to new growth. Nutrient differ markedly in their mobility within the plant.
Table 1. Mobility of nutrients within plants.
Mobile = Retranslocated from old leaves to new growth under all conditions
Variable Mobility = Retranslocated from old leaves to new growth only under some conditions
Immobile = Not retranslocated from old leaves to new growth under any conditions
Nutrients such as nitrogen, phosphorus and potassium are readily translocated from old leaves to new growth. Hence, symptoms of these deficiencies occurs initially in the older leaves. Nutrients such as calcium and boon do not appear to be retranslocated from old leaves to new growth under any circumstances. Hence, for these nutrients, deficiency symptoms occur generally in young growing areas of the plant.
For many nutrients, the extent of retranslocation is variable, depending upon the degree of the deficiency, the plant species, and the nitrogen status of the plant. For example, there is little or no movement of copper, zinc, or molybdenum out of old leaves of deficient plants. For these nutrients, symptoms will occur mainly in young tissues.
For nutrients where nitrogen supply affects the movement of other nutrients from old leaves to new growth, the location of symptoms may vary with fluctuation in the nitrogen supply. An example of this is the effect of nitrogen supply on the location of sulfur deficiency. In plants with an abundant supply of nitrogen, symptoms of sulfur deficiency occur initially on young leaves. However, in plants with a marginal supply of nitrogen, sulfur-deficient plants are generally pale and symptoms occur initially in the older leaves.