as trace elements, though because they are needed in relatively large amounts they are
sometimes known as secondary nutrients.
K Diseases
Also known as deficiency disorders, these cause symptoms to be shown by plants when
there is either an absence or a shortage of one or more of these elements in the soil.
Conversely, if these elements are present in excessive amounts some plants may
suffer from trace element toxicity—for example, soybean leaves shrivel and fall off
when there is excessive boron present in the soil.
There are two main types of deficiency diseases:
- Direct —when the reserves of the trace element in the soil are either too low or are
not present at all, and - Induced—when the trace element is present in the soil, but is either unavailable or
less available for use by the plant due to another factor such as the soil pH or soil
reserves of other nutrients—some examples are given below:
Soil Deficiency symptoms shown
Acid (low pH)
Alkaline (high pH)
With excess Phosphate (P)
With excess Potash (K) or Calcium (Ca)
With excess Copper (Cu)Molybdenum (Mo)
Manganese (Mn) and/or Iron (Fe)
Zinc (Zn)
Magnesium (Mg)
Iron (Fe)Remedies
In most cases direct deficiencies can be corrected by soil applications, where the soluble
salt of the missing element is sprayed or spread onto the soil surface and then worked in.
Foliar treatments are also used, which is normally more effective when applied to young
plants than mature ones.
Similarly, induced deficiencies can be corrected by foliar applications; a dilute
solution of a salt, or a neutralised sulphate of the element concerned is sprayed onto the
leaves of young plants.
Avoiding Trouble with Trace Elements
Soil which contains a healthy level of organic matter is unlikely to suffer from trace
element deficiencies, and food growers who regularly give their soil either animal
manure, compost or sewage sludge rarely have this problem.
If this is not practicable in the short term there is usually some remedy which can
correct the deficiency or excess, as shown on page 28 under “Correcting Trace
to cure it, by maintaining an adequate level of organic matter in the soil.
Element Deficiencies ”. It is not a good idea to make a general practice of this, but
in an emergency the deficiency can usually be remedied, as this list shows. In the
long term however it is much better practice to prevent the problem rather than try